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Since its initial discovery over 50 years ago, understanding the evolution of the vertebrate adaptive immune response has been a major area of research focus for comparative geneticists. However, how the evolutionary novelty of an adaptive immune response impacted the diversity of receptors associated with the innate immune response has received considerably less attention until recently. Here we investigate the diversification of vertebrate Toll-like receptors (TLRs), one of the most ancient and well conserved innate immune receptor families found across the Tree of Life, integrating genomic data that represent all major vertebrate lineages with new transcriptomic data from Polypteriformes, the earliest diverging ray-finned fish lineage. Our analyses reveal TLR sequences that reflect the 6 major TLR subfamilies, TLR1, TLR3, TLR4, TLR5, TLR7, and TLR11, and also currently unnamed, yet phylogenetically distinct TLR clades. We additionally recover evidence for a pulse of gene gain coincident with the rise of the adaptive immune response in jawed vertebrates, followed by a period of rapid gene loss during the Cretaceous. These gene losses are primarily concentrated in marine teleost fish and synchronous with the mid Cretaceous anoxic event, a period of rapid extinction for marine species. Finally, we reveal a mismatch between phylogenetic placement and gene nomenclature for up to 50% of TLRs found in clades such as ray-finned fishes, cyclostomes, amphibians, and elasmobranchs. Collectively these results provide an unparalleled perspective of TLR diversity, and offer a ready framework for testing gene annotations in non-model species.

Following the draft sequence of the first human genome over 20 years ago, we have achieved unprecedented insights into the rules governing its evolution, often with direct translational relevance to specific diseases. However, staggering sequence complexity has also challenged the development of a more comprehensive understanding of human genome biology. In this context, interspecific genomic studies between humans and other animals have played a critical role in our efforts to decode human gene families. In this review, we focus on how the rapid surge of genome sequencing of both model and non-model organisms now provides a broader comparative framework poised to empower novel discoveries. We begin with a general overview of how comparative approaches are essential for understanding gene family evolution in the human genome, followed by a discussion of analyses of gene expression. We show how homology can provide insights into the genes and gene families associated with immune response, cancer biology, vision, chemosensation, and metabolism, by revealing similarity in processes among distant species. We then explain methodological tools that provide critical advances and show the limitations of common approaches. We conclude with a discussion of how these investigations position us to gain fundamental insights into the evolution of gene families among living organisms in general. We hope that our review catalyzes additional excitement and research on the emerging field of comparative genomics, while aiding the placement of the human genome into its existentially evolutionary context.

Over 99% of ray-finned fishes (Actinopterygii) are teleosts, a clade that comprises half of all living vertebrates that have diversified across virtually all fresh and saltwater ecosystems. This ecological diversity raises the question of how the immunogenetic diversity required to persist under heterogeneous pathogen pressures evolved. The teleost genome duplication (TGD) has been hypothesized as the evolutionary event that provided the genomic substrate for rapid genomic evolution and innovation. However, studies of putative teleost-specific innate immune receptors have been largely limited to comparisons either among teleosts or between teleosts and distantly related vertebrate clades such as tetrapods. Here we describe and characterize the receptor diversity of two clustered innate immune gene families in the teleost sister lineage: Holostei (bowfin and gars). Using genomic and transcriptomic data, we provide a detailed investigation of the phylogenetic history and conserved synteny of gene clusters encoding diverse immunoglobulin domain-containing proteins (DICPs) and novel immune-type receptors (NITRs). These data demonstrate an ancient linkage of DICPs to the major histocompatibility complex (MHC) and reveal an evolutionary origin of NITR variable-joining (VJ) exons that predate the TGD by at least 50 million years. Further characterizing the receptor diversity of Holostean DICPs and NITRs illuminates a sequence diversity that rivals the diversity of these innate immune receptor families in many teleosts. Taken together, our findings provide important historical context for the evolution of these gene families that challenge prevailing expectations concerning the consequences of the TGD during actinopterygiian evolution.

Lipopolysaccharide (LPS)-induced signaling through Toll-like receptor 4 (TLR4) is mediated by the plasma membrane lipid, phosphatidylinositol (4,5)-bisphosphate [PI(4,5)P(2)] and its derivatives diacylglycerol and inositol trisphosphate. Levels of PI(4,5)P(2) are controlled enzymatically and fluctuate in LPS-stimulated cells. Recently, transmembrane protein 150A (TMEM150A/TM6P1/damage-regulated autophagy modulator 5) has been shown to regulate PI(4,5)P(2) production at the plasma membrane by modifying the composition of the phosphatidylinositol 4-kinase enzyme complex. To determine if TMEM150A function impacts TLR4 signaling, TMEM150A was knocked down in TLR4-expressing epithelial cells and cytokine expression quantified after LPS stimulation. In general, decreased expression of TMEM150A led to increased levels of LPS-induced cytokine secretion and transcript levels. Unexpectedly, knockdown of TMEM150A in a lung epithelial cell line (H292) also led to increased cytokine levels in the unstimulated conditions suggesting TMEM150A plays an important role in cellular homeostasis. Future studies will investigate if TMEM150A plays a similar role for other TLR agonists and in other cell lineages.

Multiple novel immunoglobulin-like transcripts (NILTs) have been identified from salmon, trout and carp. NILTs typically encode activating or inhibitory transmembrane receptors with extracellular immunoglobulin (Ig) domains. Although predicted to provide immune recognition in ray-finned fish, we currently lack a definitive framework of NILT diversity, thereby limiting our predictions for their evolutionary origin and function. In order to better understand the diversity of NILTs and their possible roles in immune function, we identified five NILT loci in the Atlantic salmon (Salmo salar) genome, defined 86 NILT Ig domains within a 3 Mbp region of zebrafish (Danio rerio) chromosome 1, and described 41 NILT Ig domains as part of an alternative haplotype for this same genomic region. We then identified transcripts encoded by 43 different NILT genes which reflect an unprecedented diversity of Ig domain sequences and combinations for a family of non-recombining receptors within a single species. Zebrafish NILTs include a sole putative activating receptor but extensive inhibitory and secreted forms as well as membrane-bound forms with no known signaling motifs. These results reveal a higher level of genetic complexity, interindividual variation and sequence diversity for NILTs than previously described, suggesting that this gene family likely plays multiple roles in host immunity.

Relapse and refractory T-cell acute lymphoblastic leukemia (T-ALL) has a poor prognosis, and new combination therapies are sorely needed. Here, we used an ex vivo high-throughput screening platform to identify drug combinations that kill zebrafish T-ALL and then validated top drug combinations for preclinical efficacy in human disease. This work uncovered potent drug synergies between AKT/mTORC1 (mammalian target of rapamycin complex 1) inhibitors and the general tyrosine kinase inhibitor dasatinib. Importantly, these same drug combinations effectively killed a subset of relapse and dexamethasone-resistant zebrafish T-ALL. Clinical trials are currently underway using the combination of mTORC1 inhibitor temsirolimus and dasatinib in other pediatric cancer indications, leading us to prioritize this therapy for preclinical testing. This combination effectively curbed T-ALL growth in human cell lines and primary human T-ALL and was well tolerated and effective in suppressing leukemia growth in patient-derived xenografts (PDX) grown in mice. Mechanistically, dasatinib inhibited phosphorylation and activation of the lymphocyte-specific protein tyrosine kinase (LCK) to blunt the T-cell receptor (TCR) signaling pathway, and when complexed with mTORC1 inhibition, induced potent T-ALL cell killing through reducing MCL-1 protein expression. In total, our work uncovered unexpected roles for the LCK kinase and its regulation of downstream TCR signaling in suppressing apoptosis and driving continued leukemia growth. Analysis of a wide array of primary human T-ALLs and PDXs grown in mice suggest that combination of temsirolimus and dasatinib treatment will be efficacious for a large fraction of human T-ALLs.

Currently assessment of the potential immunotoxicity of a given agent involves a tiered approach for hazard identification and mechanistic studies, including observational studies, evaluation of immune function, and measurement of susceptibility to infectious and neoplastic diseases. These studies generally use costly low-throughput mammalian models. Zebrafish, however, offer an excellent alternative due to their rapid development, ease of maintenance, and homology to mammalian immune system function and development. Larval zebrafish also are a convenient model to study the innate immune system with no interference from the adaptive immune system. In this study, a respiratory burst assay (RBA) was utilized to measure reactive oxygen species (ROS) production after developmental xenobiotic exposure. Embryos were exposed to non-teratogenic doses of chemicals and at 96 hr post-fertilization, the ability to produce ROS was measured. Using the RBA, 12 compounds with varying immune-suppressive properties were screened. Seven compounds neither suppressed nor enhanced the respiratory burst; five reproducibly suppressed global ROS production, but with varying potencies: benzo[a]pyrene, 17β-estradiol, lead acetate, methoxychlor, and phenanthrene. These five compounds have all previously been reported as immunosuppressive in mammalian innate immunity assays. To evaluate whether the suppression of ROS by these compounds was a result of decreased immune cell numbers, flow cytometry with transgenic zebrafish larvae was used to count the numbers of neutrophils and macrophages after chemical exposure. With this assay, benzo[a]pyrene was found to be the only chemical that induced a change in the number of immune cells by increasing macrophage but not neutrophil numbers. Taken together, this work demonstrates the utility of zebrafish larvae as a vertebrate model for identifying compounds that impact innate immune function at non-teratogenic levels, and validates measuring ROS production and phagocyte numbers as metrics for monitoring how xenobiotic exposure alters the innate immune system.

Briefly considered extinct in the wild, the future of the wild population of the Wyoming toad (Anaxyrus baxteri) continues to rely on captive breeding to supplement the wild population. Given its small natural geographic range and history of rapid population decline at least partly due to fungal disease, investigation of the diversity of key receptor families involved in the host immune response represents an important conservation need. Population decline may have reduced immunogenetic diversity sufficiently to increase the vulnerability of the species to infectious diseases. Here we use comparative transcriptomics to examine the diversity of toll-like receptors and major histocompatibility complex (MHC) sequences across three individual Wyoming toads. We find reduced diversity at MHC genes compared to bufonid species with a similar history of bottleneck events. Our data provide a foundation for future studies that seek to evaluate the genetic diversity of Wyoming toads, identify biomarkers for infectious disease outcomes, and guide breeding strategies to increase genomic variability and wild release successes.

The morphogenesis of left-right (LR) asymmetry is a crucial phase of organogenesis. In the digestive tract, the development of anatomical asymmetry is first evident in the leftward curvature of the stomach. To elucidate the molecular events that shape this archetypal laterality, we performed transcriptome analyses of the left versus right sides of the developing stomach in frog embryos. Besides the known LR gene pitx2, the only gene found to be expressed asymmetrically throughout all stages of curvature was single-minded 2 (sim2), a Down Syndrome-related transcription factor and homolog of a Drosophila gene (sim) required for LR asymmetric looping of the fly gut. We demonstrate that sim2 functions downstream of LR patterning cues to regulate key cellular properties and behaviors in the left stomach epithelium that drive asymmetric curvature. Our results reveal unexpected convergent cooption of single-minded genes during the evolution of LR asymmetric morphogenesis, and have implications for dose-dependent roles of laterality factors in non-laterality-related birth defects.

The bowfin (Amia calva) is a ray-finned fish that possesses a unique suite of ancestral and derived phenotypes, which are key to understanding vertebrate evolution. The phylogenetic position of bowfin as a representative of neopterygian fishes, its archetypical body plan and its unduplicated and slowly evolving genome make bowfin a central species for the genomic exploration of ray-finned fishes. Here we present a chromosome-level genome assembly for bowfin that enables gene-order analyses, settling long-debated neopterygian phylogenetic relationships. We examine chromatin accessibility and gene expression through bowfin development to investigate the evolution of immune, scale, respiratory and fin skeletal systems and identify hundreds of gene-regulatory loci conserved across vertebrates. These resources connect developmental evolution among bony fishes, further highlighting the bowfin’s importance for illuminating vertebrate biology and diversity in the genomic era., Analysis of a chromosome-level bowfin genome assembly sheds light into neopterygian fish evolution. Chromatin accessibility and gene expression profiling provides insight into bowfin embryonic development.

Background Presumed autoimmune diseases affecting the central nervous system (CNS) of dogs are common. In people, antibodies against neuronal cell surface antigens that are associated with a wide variety of neurological syndromes have been identified. The presence of cerebrospinal fluid (CSF) autoantibodies that target neuronal cell surface proteins has not been reported in dogs with neurologic disorders. Objectives Autoantibodies to neuronal cell surface antigens can be found in the CSF of dogs with inflammatory CNS disease. Our aim was to determine whether 6 neuronal cell surface autoantibodies were present in the CSF of dogs diagnosed with inflammatory and noninflammatory CNS disease. Animals Client-owned dogs with CNS disease and complete diagnostic evaluation including magnetic resonance imaging and CSF analysis were included. One healthy dog was included as a negative control. Methods Cerebrospinal fluid was tested for 6 antigenic targets with a commercially available indirect immunofluorescence assay test kit. Results There were 32 dogs with neurological disease, 19 diagnosed with inflammatory disease (encephalitis and meningitis), 10 with noninflammatory disease (neoplasia, intervertebral disk disease, degenerative myelopathy, and epilepsy), 2 with no diagnosis, and 1 with neoplasia and meningoencephalitis. Anti-N-methyl-d-aspartate receptor 1 (NMDAR1) antibodies were detected in 3 dogs (3/32; 9.38%). All 3 dogs responded to treatment of meningoencephalomyelitis of unknown etiology (MUE). Conclusions and clinical importance Further evaluation of the prevalence and clinical relevance of CSF and serum antibodies to neuronal cell surface antigens is warranted. Defining antigenic targets associated with encephalitis in dogs might allow diagnostic categorization of MUE antemortem.

The bowfin fish (Amia calva) diverged before the genome duplication in teleost fishes, and its archetypical body plan and slow rate of molecular evolution make it a key species for genomic exploration as a basal representative of the neopterygian fishes. To investigate the evolution and development of ray-finned fishes, we generated a chromosome-level genome assembly for bowfin that enables gene-order analyses which settle its long-debated, phylogenetic relationship with gars. We analyze the genomic underpinnings of the bowfin’s unique combination of derived and ancestral phenotypes involving the immune system as well as scale, respiratory organ, and skeletal development. By detailing chromatin accessibility and gene expression through bowfin development, we connect developmental gene regulatory loci across vertebrates. We illustrate the utility of these genomic resources to connect developmental evolution across bony fishes, showing the importance of bowfin in understanding vertebrate biology and diversity.

Background Advances in next-generation sequencing technologies have reduced the cost of whole transcriptome analyses, allowing characterization of non-model species at unprecedented levels. The rapid pace of transcriptomic sequencing has driven the public accumulation of a wealth of data for phylogenomic analyses, however lack of tools aimed towards phylogeneticists to efficiently identify orthologous sequences currently hinders effective harnessing of this resource. Results We introduce TOAST, an open source R software package that can utilize the ortholog searches based on the software Benchmarking Universal Single-Copy Orthologs (BUSCO) to assemble multiple sequence alignments of orthologous loci from transcriptomes for any group of organisms. By streamlining search, query, and alignment, TOAST automates the generation of locus and concatenated alignments, and also presents a series of outputs from which users can not only explore missing data patterns across their alignments, but also reassemble alignments based on user-defined acceptable missing data levels for a given research question. Conclusions TOAST provides a comprehensive set of tools for assembly of sequence alignments of orthologs for comparative transcriptomic and phylogenomic studies. This software empowers easy assembly of public and novel sequences for any target database of candidate orthologs, and fills a critically needed niche for tools that enable quantification and testing of the impact of missing data. As open-source software, TOAST is fully customizable for integration into existing or novel custom informatic pipelines for phylogenomic inference. Software, a detailed manual, and example data files are available through github carolinafishes.github.io

Upon binding to thalidomide and other immunomodulatory drugs, the E3 ligase substrate receptor cereblon (CRBN) promotes proteosomal destruction by engaging the DDB1–CUL4A–Roc1–RBX1 E3 ubiquitin ligase in human cells but not in mouse cells, suggesting that sequence variations in CRBN may cause its inactivation. Therapeutically, CRBN engagers have the potential for broad applications in cancer and immune therapy by specifically reducing protein expression through targeted ubiquitin-mediated degradation. To examine the effects of defined sequence changes on CRBN's activity, we performed a comprehensive study using complementary theoretical, biophysical, and biological assays aimed at understanding CRBN's nonprimate sequence variations. With a series of recombinant thalidomide-binding domain (TBD) proteins, we show that CRBN sequence variants retain their drug-binding properties to both classical immunomodulatory drugs and dBET1, a chemical compound and targeting ligand designed to degrade bromodomain-containing 4 (BRD4) via a CRBN-dependent mechanism. We further show that dBET1 stimulates CRBN's E3 ubiquitin–conjugating function and degrades BRD4 in both mouse and human cells. This insight paves the way for studies of CRBN-dependent proteasome-targeting molecules in nonprimate models and provides a new understanding of CRBN's substrate-recruiting function.

The vertebrate immune response comprises multiple molecular and cellular components that interface to provide defense against pathogens. Because of the dynamic complexity of the immune system and its interdependent innate and adaptive functionality, an understanding of the whole-organism response to pathogen exposure remains unresolved. Zebrafish larvae provide a unique model for overcoming this obstacle, because larvae are protected against pathogens while lacking a functional adaptive immune system during the first few weeks of life. Zebrafish larvae were exposed to immune agonists for various lengths of time, and a microarray transcriptome analysis was executed. This strategy identified known immune response genes, as well as genes with unknown immune function, including the E3 ubiquitin ligase tripartite motif-9 (Trim9). Although trim9 expression was originally described as “brain specific,” its expression has been reported in stimulated human Mϕs. In this study, we found elevated levels of trim9 transcripts in vivo in zebrafish Mϕs after immune stimulation. Trim9 has been implicated in axonal migration, and we therefore investigated the impact of Trim9 disruption on Mϕ motility and found that Mϕ chemotaxis and cellular architecture are subsequently impaired in vivo. These results demonstrate that Trim9 mediates cellular movement and migration in Mϕs as well as neurons.

The resolution of the gar genome affords an opportunity to examine the diversification and functional specialization of immune effector molecules at a distant and potentially informative point in phylogenetic development. Although innate immunity is effected by a particularly large number of different families of molecules, the focus here is to provide detailed characterization of several families of innate receptors that are encoded in large multigene families, for which orthologous forms can be identified in other species of bony fish but not in other vertebrate groups as well as those for which orthologs are present in other vertebrate species. The results indicate that although teleost fish and the gar, as a holostean reference species, share gene families thought previously to be restricted to the teleost fish, the manner in which the members of the multigene families of innate immune receptors have undergone diversification is different in these two major phylogenetic radiations. It appears that both the total genome duplication and different patterns of genetic selection have influenced the derivation and stabilization of innate immune genes in a substantial manner during the course of vertebrate evolution.

Metastasis accounts for the majority of all cancer deaths, yet the process remains poorly understood. A pivotal step in the metastasis process is the exiting of tumor cells from the circulation, a process known as extravasation. However, it is unclear how tumor cells extravasate and whether multicellular clusters of tumor cells possess the ability to exit as a whole or must first disassociate. In this study, we use in vivo zebrafish and mouse models to elucidate the mechanism tumor cells use to extravasate. We found that circulating tumor cells exit the circulation using the recently identified extravasation mechanism, angiopellosis, and do so as both clusters and individual cells. We further show that when melanoma and cervical cancer cells utilize this extravasation method to exit as clusters, they exhibit an increased ability to form tumors at distant sites through the expression of unique genetic profiles. Collectively, we present a new model for tumor cell extravasation of both individual and multicellular circulating tumor cells. This article has an associated First Person interview with the first author of the paper.

Multiple novel immunoglobulin-like transcripts (NILTs) have been identified from salmon, trout and carp. NILTs typically encode activating or inhibitory transmembrane receptors with extracellular immunoglobulin (Ig) domains. Although predicted to provide some level of immune recognition in ray-finned fish, we currently lack a definitive framework of NILT diversity, thereby challenging our ability to understand the evolutionary origin and specific function of these genes. In order to better understand the diversity of NILT genes and their possible roles in immune function, we identified 5 NILT loci in the Atlantic salmon (Salmo salar) genome, defined 86 NILT Ig domains within a 3 Mbp region of zebrafish (Danio rerio) chromosome 1, and described 41 NILT Ig domains as part of an alternate haplotype for this same genomic region. We then identified transcripts that define 43 different NILT genes and reflect an unprecedented range of sequence diversity and combinatorial diversity of Ig domains for a single family of non-recombining receptors. Zebrafish NILTs include a single putative activating receptor but extensive inhibitory and secreted forms as well as membrane-bound forms with no known signaling motifs. Whole genome sequences from different genetic backgrounds reveal at least three alternative haplotypes of the zebrafish NILT gene cluster that display gene content variation. This observation indicates that different individual fish can encode different combinations of NILTs which could impact their immune function. Furthermore, these results reveal a higher level of genetic complexity and sequence diversity for NILTs than previously described, suggesting that this gene family likely plays multiple roles in host immunity.

Modern genetics research has resulted in significant advances in cell in vitro microinjection systems. Such systems provide biological and medical practitioners with high volume cell throughput and statistically relevant data. This paper provides the reader with a comprehensive review of the major research technologies used in automated cell microinjection and of their individual subsystems. Microinjection subsystems reviewed include machine vision, nonvision sensors and user interface (input), cell modeling, piercing mechanisms and injection control loop (control), cell holder and manipulator, and microinjection (output). The interdisciplinary technologies reviewed for microinjection sensing, automation, and control include microfluidic actuation, optical field actuation (optical trapping and optical guidance), electrical field actuation (electrorotation, electrowetting, and dielectrophoresis), and ultrasonic vibration. The survey concludes that research into automated microinjection systems will focus on reducing the scale of microinjection systems and developing appropriate controllers.

The regulation of caspase-3 enzyme activity is a vital process in cell fate decisions leading to cell differentiation and tissue development or to apoptosis. The zebrafish, Danio rerio, has become an increasingly popular animal model to study several human diseases because of their transparent embryos, short reproductive cycles, and ease of drug administration. While apoptosis is an evolutionarily conserved process in metazoans, little is known about caspases from zebrafish, particularly regarding substrate specificity and allosteric regulation compared to the human caspases. We cloned zebrafish caspase-3a (casp3a) and examined substrate specificity of the recombinant protein, Casp3a, compared to human caspase-3 (CASP3) by utilizing M13 bacteriophage substrate libraries that incorporated either random amino acids at P5-P1′ or aspartate fixed at P1. The results show a preference for the tetrapeptide sequence DNLD for both enzymes, but the P4 position of zebrafish Casp3a also accommodates valine equally well. We determined the structure of zebrafish Casp3a to 2.28A resolution by X-ray crystallography, and when combined with molecular dynamics simulations, the results suggest that a limited number of amino acid substitutions near the active site result in plasticity of the S4 sub-site by increasing flexibility of one active site loop and by affecting hydrogen-bonding with substrate. The data show that zebrafish Casp3a exhibits a broader substrate portfolio, suggesting overlap with the functions of caspase-6 in zebrafish development.

Stem cells possess the ability to home in and travel to damaged tissue when injected intravenously. For the cells to exert their therapeutic effect, they must cross the blood vessel wall and enter the surrounding tissues. The mechanism of extravasation injected stem cells employ for exit has yet to be characterized. Using intravital microscopy and a transgenic zebrafish line Tg(fli1a:egpf) with GFP-expressing vasculature, we documented the detailed extravasation processes in vivo for injected stem cells in comparison to white blood cells (WBCs). While WBCs left the blood vessels by the standard diapedesis process, injected cardiac and mesenchymal stem cells underwent a distinct method of extravasation that was markedly different from diapedesis. Here, the vascular wall undergoes an extensive remodeling to allow the cell to exit the lumen, while the injected cell remains distinctively passive in activity. We termed this process Angio-pello-sis, which represents an alternative mechanism of cell extravasation to the prevailing theory of diapedesis. Video Highlight: https://youtu.be/i5EI-ZvhBps

Moore et al. reports the first single-cell gene expression analysis in zebrafish blood to distinguish major blood lineages, identify new cell types, and delineate heterogeneity in T cell leukemia., Hematopoiesis culminates in the production of functionally heterogeneous blood cell types. In zebrafish, the lack of cell surface antibodies has compelled researchers to use fluorescent transgenic reporter lines to label specific blood cell fractions. However, these approaches are limited by the availability of transgenic lines and fluorescent protein combinations that can be distinguished. Here, we have transcriptionally profiled single hematopoietic cells from zebrafish to define erythroid, myeloid, B, and T cell lineages. We also used our approach to identify hematopoietic stem and progenitor cells and a novel NK-lysin 4+ cell type, representing a putative cytotoxic T/NK cell. Our platform also quantified hematopoietic defects in rag2E450fs mutant fish and showed that these fish have reduced T cells with a subsequent expansion of NK-lysin 4+ cells and myeloid cells. These data suggest compensatory regulation of the innate immune system in rag2E450fs mutant zebrafish. Finally, analysis of Myc-induced T cell acute lymphoblastic leukemia showed that cells are arrested at the CD4+/CD8+ cortical thymocyte stage and that a subset of leukemia cells inappropriately reexpress stem cell genes, including bmi1 and cmyb. In total, our experiments provide new tools and biological insights into single-cell heterogeneity found in zebrafish blood and leukemia.

Three sequence lineages of MHC class I genes have been described in zebrafish (Danio rerio): U, Z, and L. The U lineage genes encoded on zebrafish chromosome 19 are predicted to provide the classical function of antigen presentation. This MHC class I locus displays significant haplotypic variation and is the only MHC class I locus in zebrafish that shares conserved synteny with the core mammalian MHC. Here we describe two MHC class I U lineage genes, mhc1ula and mhc1uma, that map to chromosome 22. Unlike the U lineage proteins encoded on chromosome 19, Ula and Uma likely play a nonclassical role as they lack conservation of key peptide binding residues, display limited polymorphic variation, and exhibit tissue-specific expression. We also describe a null haplotype at this chromosome 22 locus in which the mhc1ula and mhc1uma genes are absent due to a ∼30 kb deletion with no other MHC class I sequences present. Functional and non-functional transcripts of mhc1ula and mhc1uma were identified; however, mhc1uma transcripts were often not amplified or amplified at low levels from individuals possessing an apparently bona fide gene. These distinct U lineage genes may be restricted to the superorder Ostariophysi as similar sequences only could be identified from the blind cavefish (Astyanyx mexicanus), fathead minnow (Pimephales promelas), goldfish (Carassius auratus), and grass carp (Ctenopharyngodon idellus).

Mitochondria are known primarily as the location of the electron transport chain and energy production in cells. More recently, mitochondria have been shown to be signaling centers for apoptosis and inflammation. Reactive oxygen species (ROS) generated as by-products of the electron transport chain within mitochondria significantly impact cellular signaling pathways. Because of the toxic nature of ROS, mitochondria possess an antioxidant enzyme, superoxide dismutase 2 (SOD2), to neutralize ROS. If mitochondrial antioxidant enzymes are overwhelmed during severe infections, mitochondrial dysfunction can occur and lead to multiorgan failure or death. Pseudomonas aeruginosa is an opportunistic pathogen that can infect immunocompromised patients. Infochemicals and exotoxins associated with P. aeruginosa are capable of causing mitochondrial dysfunction. In this work, we describe the roles of SOD2 and mitochondrial ROS regulation in the zebrafish innate immune response to P. aeruginosa infection. sod2 is upregulated in mammalian macrophages and neutrophils in response to lipopolysaccharide in vitro , and sod2 knockdown in zebrafish results in an increased bacterial burden. Further investigation revealed that phagocyte numbers are compromised in Sod2-deficient zebrafish. Addition of the mitochondrion-targeted ROS-scavenging chemical MitoTEMPO rescues neutrophil numbers and reduces the bacterial burden in Sod2-deficient zebrafish. Our work highlights the importance of mitochondrial ROS regulation by SOD2 in the context of innate immunity and supports the use of mitochondrion-targeted ROS scavengers as potential adjuvant therapies during severe infections.

Complex cytoplasmic nucleotide-sensing mechanisms can recognize foreign DNA based on a lack of methylation and initiate an immune response to clear the infection. Zebrafish embryos with global DNA hypomethylation caused by mutations in the ubiquitin-like with PHD and ring finger domains 1 (uhrf1) or DNA methyltransferase 1 (dnmt1) genes exhibit a robust interferon induction characteristic of the first line of defense against viral infection. We found that this interferon induction occurred in non-immune cells and examined whether intracellular viral sensing pathways in these cells were the trigger. RNA-seq analysis of uhrf1 and dnmt1 mutants revealed widespread induction of Class I retrotransposons and activation of cytoplasmic DNA viral sensors. Attenuating Sting, phosphorylated Tbk1 and, importantly, blocking reverse transcriptase activity suppressed the expression of interferon genes in uhrf1 mutants. Thus, activation of transposons in cells with global DNA hypomethylation mimics a viral infection by activating cytoplasmic DNA sensors. This suggests that antiviral pathways serve as surveillance of cells that have derepressed intragenomic parasites due to DNA hypomethylation.

Comparative functional genomic studies require the proper identification of gene orthologs to properly exploit animal biomedical research models. To identify gene orthologs, comprehensive, conserved gene synteny analyses are necessary to unwind gene histories that are convoluted by two rounds of early vertebrate genome duplication, and in the case of the teleosts, a third round, the teleost genome duplication (TGD). Recently, the genome of the spotted gar, a holostean outgroup to the teleosts that did not undergo this third genome duplication, was sequenced and applied as an orthology bridge to facilitate the identification of teleost orthologs to human genes and to enhance the power of teleosts as biomedical models. In this study, we apply the spotted gar orthology bridge to help describe the gene history of the vertebrate TNFAIP8 family. Members of the TNFAIP8 gene family have been linked to regulation of immune function and homeostasis and the development of multiple cancer types. Through a conserved gene synteny analysis, we identified zebrafish orthologs to human TNFAIP8L1 and TNFAIP8L3 genes and two co-orthologs to human TNFAIP8L2, but failed to identify an ortholog to human TNFAIP8. Through the application of the orthology bridge, we determined that teleost orthologs to human TNFAIP8 genes were likely lost in a genome inversion event after their divergence from their common ancestor with spotted gar. These findings demonstrate the value of this enhanced approach to gene history analysis and support the development of teleost models to study complex questions related to an array of biomedical issues, including immunity and cancer.

The polymeric immunoglobulin (Ig) receptor (pIgR) is an integral transmembrane glycoprotein that plays an important role in the mammalian immune response by transporting soluble polymeric Igs across mucosal epithelial cells. Single pIgR genes, which are expressed in lymphoid organs including mucosal tissues, have been identified in several teleost species. A single pigr gene has been identified on zebrafish chromosome 2 along with a large multigene family consisting of 29 pigr-like (PIGRL) genes. Full-length transcripts from ten different PIGRL genes that encode secreted and putative inhibitory membrane-bound receptors have been characterized. Although PIGRL and pigr transcripts are detected in immune tissues, only PIGRL transcripts can be detected in lymphoid and myeloid cells. In contrast to pIgR which binds Igs, certain PIGRL proteins bind phospholipids. PIGRL transcript levels are increased after infection with Streptococcus iniae, suggesting a role for PIGRL genes during bacterial challenge. Transcript levels of PIGRL genes are decreased after infection with Snakehead rhabdovirus, suggesting that viral infection may suppress PIGRL function.

Antigen processing and presentation genes found within the MHC are among the most highly polymorphic genes of vertebrate genomes, providing populations with diverse immune responses to a wide array of pathogens. Here, we describe transcriptome, exome, and whole-genome sequencing of clonal zebrafish, uncovering the most extensive diversity within the antigen processing and presentation genes of any species yet examined. Our CG2 clonal zebrafish assembly provides genomic context within a remarkably divergent haplotype of the core MHC region on chromosome 19 for six expressed genes not found in the zebrafish reference genome: mhc1uga, proteasome-β 9b (psmb9b), psmb8f, and previously unknown genes psmb13b, tap2d, and tap2e We identify ancient lineages for Psmb13 within a proteasome branch previously thought to be monomorphic and provide evidence of substantial lineage diversity within each of three major trifurcations of catalytic-type proteasome subunits in vertebrates: Psmb5/Psmb8/Psmb11, Psmb6/Psmb9/Psmb12, and Psmb7/Psmb10/Psmb13. Strikingly, nearby tap2 and MHC class I genes also retain ancient sequence lineages, indicating that alternative lineages may have been preserved throughout the entire MHC pathway since early diversification of the adaptive immune system ∼500 Mya. Furthermore, polymorphisms within the three MHC pathway steps (antigen cleavage, transport, and presentation) are each predicted to alter peptide specificity. Lastly, comparative analysis shows that antigen processing gene diversity is far more extensive than previously realized (with ancient coelacanth psmb8 lineages, shark psmb13, and tap2t and psmb10 outside the teleost MHC), implying distinct immune functions and conserved roles in shaping MHC pathway evolution throughout vertebrates.

The regulation of caspase‐3 enzyme activity is a vital process in cell fate decisions leading to cell differentiation and tissue development or to apoptosis. The zebrafish, Danio rerio, has become an increasingly popular animal model to study several human diseases because of their transparent embryos, short reproductive cycles, and ease of drug administration. While apoptosis is an evolutionarily conserved process in metazoans, little is known about caspases from zebrafish, particularly regarding substrate specificity and allosteric regulation compared to the human caspases. We cloned zebrafish caspase‐3a (casp3a) and examined substrate specificity of the recombinant protein, Casp3a, compared to human caspase‐3 (CASP3) by utilizing M13 bacteriophage substrate libraries that incorporated either random amino acids at P5‐P1′ or aspartate fixed at P1. The results show a preference for the tetrapeptide sequence DNLD for both enzymes, but the P4 position of zebrafish Casp3a also accommodates valine equally well. We determined the structure of zebrafish Casp3a to 2.28Å resolution by X‐ray crystallography, and when combined with molecular dynamics simulations, the results suggest that a limited number of amino acid substitutions near the active site result in plasticity of the S4 sub‐site by increasing flexibility of one active site loop and by affecting hydrogen‐bonding with substrate. The data show that zebrafish Casp3a exhibits a broader substrate portfolio, suggesting overlap with the functions of caspase‐6 in zebrafish development.

Teleost genomes encode multiple multigene families of immunoglobulin domain-containing innate immune receptors (IIIRs) with unknown function and no clear mammalian orthologs. However, the genomic organization of IIIR gene clusters and the structure and signaling motifs of the proteins they encode are similar to those of mammalian innate immune receptor families such as the killer cell immunoglobulin-like receptors (KIRs), leukocyte immunoglobulin-like receptors (LILRs), Fc receptors, triggering receptors expressed on myeloid cells (TREMs) and CD300s. Teleost IIIRs include novel immune-type receptors (NITRs); diverse immunoglobulin domain containing proteins (DICPs); polymeric immunoglobulin receptor-like proteins (PIGRLs); novel immunoglobulin-like transcripts (NILTs) and leukocyte immune-type receptors (LITRs). The accumulation of genomic sequence data has revealed that IIIR gene clusters in zebrafish display haplotypic and gene content variation. This intraspecific genetic variation, as well as significant interspecific variation, frequently confounds the identification of definitive orthologous IIIR sequences between teleost species. Nevertheless, by defining which teleost lineages encode (and do not encode) different IIIR families, predictions can be made about the presence (or absence) of specific IIIR families in each teleost lineage. It is anticipated that further investigations into available genomic resources and the sequencing of a variety of multiple teleost genomes will identify additional IIIR families and permit the modeling of the evolutionary origins of IIIRs.

Bony fish encode multiple multi-gene families of membrane receptors that are comprised of immunoglobulin (Ig) domains and are predicted to function in innate immunity. One of these families, the diverse immunoglobulin (Ig) domain-containing protein (DICP) genes, maps to three chromosomal loci in zebrafish. Most DICPs possess one or two Ig ectodomains and include membrane-bound and secreted forms. Membrane-bound DICPs include putative inhibitory and activating receptors. Recombinant DICP Ig domains bind lipids with varying specificity, a characteristic shared with mammalian CD300 and TREM family members. Numerous DICP transcripts amplified from different lines of zebrafish did not match the zebrafish reference genome sequence suggesting polymorphic and haplotypic variation. The expression of DICPs in three different lines of zebrafish has been characterized employing PCR-based strategies. Certain DICPs exhibit restricted expression in adult tissues whereas others are expressed ubiquitously. Transcripts of a subset of DICPs can be detected during embryonic development suggesting roles in embryonic immunity or other developmental processes. Transcripts representing eleven previously uncharacterized DICP sequences were identified. The assignment of two of these sequences to an unplaced genomic scaffold resulted in the identification of an alternative DICP haplotype that is linked to a MHC class I Z lineage haplotype on zebrafish chromosome 3. The linkage of DICP and MHC Class I genes also is observable in the genomes of the related grass carp (Ctenopharyngodon idellus) and common carp (Cyprinus carpio) suggesting that this is a shared character with the last common Cyprinidae ancestor.

Devices containing III–V semiconductors such as InAs are increasingly being used in the electronic industry for a variety of optoelectronic applications. Furthermore, the attractive chemical, material, electronic properties make such materials appealing for use in devices designed for biological applications, such as biosensors. However, in biological applications the leaching of toxic materials from these devices could cause harm to cells or tissue. Additionally, after disposal, toxic inorganic materials can leach from devices and buildup in the environment, causing long-term ecological harm. Therefore, the toxicity of these materials along with their stability in physiological conditions are important factors to consider. Surface modifications are one common method of stabilizing semiconductor materials in order to chemically and electronically passivate them. Such surface modifications could also prevent the leaching of toxic materials by preventing the regrowth of the unstable surface oxide layer and by creating an effective barrier between the semiconductor surface and the surrounding environment. In this study, various surface modifications on InAs are developed with the goal of decreasing the leaching of indium and arsenic. The leaching of indium and arsenic from modified substrates was assessed in physiological conditions using inductively coupled plasma mass spectrometry (ICP-MS). Substrates modified with 11-mercapto-1-undecanol (MU) and graft polymerized with poly(ethylene) glycol (PEG) were most effective at preventing indium and arsenic leaching. These surfaces were characterized using contact angle analysis, ellipsometry, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). Substrates modified with collagen and synthetic polyelectrolytes were least effective, due to the destructive nature of acidic environments on InAs. The toxicity of modified and unmodified InAs, along with raw indium, arsenic, and PEG components was assessed using zebrafish embryos.

Natural killer (NK) cells effect a form of innate immunity that recognizes and eliminates cells that are infected with certain viruses or have undergone malignant transformation. In mammals, this recognition can be mediated through immunoglobulin- (Ig) and/or lectin-type NK receptors (NKRs). NKR genes in mammals range from minimally polymorphic single copy genes to complex multigene families that exhibit high levels of haplotypic complexity and exhibit significant interspecific variation. Certain single copy NKR genes that are present in one mammal are present as expanded multi-gene families in other mammals. These observations highlight NKRs as one of the most rapidly evolving eukaryotic gene families and likely reflect the influence of pathogens, especially viruses, on their evolution. Although well characterized in human and mice, cytotoxic cells that are functionally similar to NK cells have been identified in species ranging from birds to reptiles, amphibians and fish. Although numerous receptors have been identified in non-mammalian vertebrates that share structural relationships with mammalian NKRs, functionally defining these lower vertebrate molecules as NKRs is confounded by methodological and interpretive complexities. Nevertheless, several lines of evidence suggest that NK-type function or its equivalent has sustained a long evolutionary history throughout vertebrate species.

The Sp family of transcription factors is required for the expression of cell cycle- and developmentally regulated genes, and the deregulated expression of a handful of family members is associated with human tumorigenesis. Sp2 is a relatively poorly characterized member of the Sp family that, although widely expressed, exhibits little or no DNA binding or transcriptional activity in human and mouse cell lines. To begin to address the role(s) played by Sp2 in early metazoan development we have cloned and characterized Sp2 from zebrafish (Danio rerio). We report that 1) the intron/exon organization and amino acid sequence of zebrafish Sp2 is closely conserved with its mammalian orthologues, 2) zebrafish Sp2 weakly stimulates an Sp-dependent promoter in vitro and associates with the nuclear matrix in a DNA-independent fashion, 3) zebrafish Sp2 is inherited as a maternal transcript, is transcribed in zebrafish embryos and adult tissues, and is required for completion of gastrulation, and 4) zebrafish lines carrying transgenes regulated by the Sp2 promoter recapitulate patterns of endogenous Sp2 expression.

Detailed knowledge of the external regulation of gene func-tion is a fundamental necessity in order to annotate sequencedgenomes and to understand biological processes in single cellsand multicellular organisms. One of the most widely used ap-proaches for the down-regulation of specific genes is the ap-plication of antisense agents. Antisense agents are oligomersthat have the ability to hybridize sequence specificslly tomRNAs, inhibiting translation and potentially leading to mRNAdegradation through RNAse H recruitment.

Large granular lymphocyte (LGL) leukemia is commonly associated with poor hematopoiesis. The first case of pulmonary artery hypertension (PAH) was observed in a 57-year-old woman with natural killer (NK)–LGL leukemia and transfusion-dependent anemia. Using a genetic approach, we demonstrated that killing of pulmonary endothelial cells by patient NK cells was mediated by dysregulated balance in activating and inhibitory NK-receptor signaling. Elevated pulmonary artery pressure and erythroid differentiation improved after disrupting the NK-receptor signaling pathway with 4 courses of a farnesyltransferase inhibitor, tipifarnib. Coincidental association between PAH and LGL leukemia suggest a causal relationship between the expanded lymphocyte population and these clinical manifestations. This trial is registered at www.ClinicalTrials.gov as NCI 6823.

Transmembrane bound receptors comprised of extracellular immunoglobulin (Ig) or lectin domains play integral roles in a large number of immune functions including inhibitory and activating responses. The function of many of the activating receptors requires a physical interaction with an adaptor protein possessing a cytoplasmic regulatory motif. The partnering of an activating receptor with an adaptor protein relies on complementary charged residues in the two transmembrane domains. The mammalian natural killer (NK) and Fc receptors (FcR) represent two of many receptor families, which possess activating receptors that partner with adaptor proteins for signaling. Zebrafish represent a powerful experimental model for understanding developmental regulation at early stages of embryogenesis and for efficiently generating transgenic animals. In an effort to understand developmental aspects of immune receptor function, we have accessed the partially annotated zebrafish genome to identify six different adaptor molecules: Dap10, Dap12, Cd3zeta, Cd3zeta-like, FcRgamma and FcRgamma-like that are homologous to those effecting immune function in mammals. Their genomic organizations have been characterized, cDNA transcripts have been recovered, phylogenetic relationships have been defined and their cell lineage-specific expression patterns have been established.

Both inhibitory and activating forms of natural killer (NK) cell receptors are found in mammals. The activating receptors play a direct role in the recognition of virally infected or transformed cells and transduce activating signals into the cell by partnering with an adaptor protein, which contains a cytoplasmic activation motif. Activating NK receptors encoded by the mammalian leukocyte receptor complex (e.g., killer cell immunoglobulin-like receptors) and the natural killer complex (e.g., Ly49s) partner with the adaptor protein DAP12, whereas NK receptors encoded in the CD94/NKG2 complex partner with the adaptor protein DAP10. Novel immune-type receptors (NITRs) found in bony fish share several common features with immunoglobulin-type NK receptors. Nitr9 is a putative activating receptor in zebrafish that induces cytotoxicity within the context of human NK cells. One isoform of Nitr9, Nitr9L, is shown here to preferentially partner with a zebrafish ortholog of Dap12. Cross-linking the Nitr9L-Dap12 complex results in activation of the phosphytidylinositol 3-kinase--AKT--extracellular signal-regulated kinase pathway suggesting that the DAP12-based activating pathway is conserved between bony fish and mammals.

The zebrafish has become a powerful tool for dissecting vertebrate gene function during embryogenesis. Numerous molecular systems have been developed to examine gene function in zebrafish, including transgenics for creating lineage-tracer lines of zebrafish that express a fluorescent protein as a marker for specific populations of cells, and antisense strategies, primarily morpholinos, for knocking down gene function. The focus of this review is to summarize the pros and cons of the currently available systems for functional genomics in zebrafish, and to discuss the need for future methodologies.

The identification of C-type lectin (Group V) natural killer (NK) cell receptors in bony fish has remained elusive. Analyses of the Fugu rubripes genome database failed to identify Group V C-type lectin domains (Zelensky and Gready, BMC Genomics 5:51, 2004) suggesting that bony fish, in general, may lack such receptors. Numerous Group II C-type lectin receptors, which are structurally similar to Group V (NK) receptors, have been characterized in bony fish. By searching the zebrafish genome database we have identified a multi-gene family of Group II immune-related, lectin-like receptors (illrs) whose members possess inhibiting and/or activating signaling motifs typical of Group V NK receptors. Illr genes are differentially expressed in the myeloid and lymphoid lineages, suggesting that they may play important roles in the immune functions of multiple hematopoietic cell lineages.

The novel immune-type receptor (NITR) genes encode a unique multigene family of leukocyte regulatory receptors, which possess an extracellular Ig variable (V) domain and may function in innate immunity. Artificial chromosomes that encode zebrafish NITRs have been assembled into a contig spanning ≈350 kb. Resolution of the complete NITR gene cluster has led to the identification of eight previously undescribed families of NITRs and has revealed the presence of C-type lectins within the locus. A maximum haplotype of 36 NITR genes (138 gene sequences in total) can be grouped into 12 distinct families, including inhibitory and activating receptors. An extreme level of interindividual heterozygosity is reflected in allelic polymorphisms, haplotype variation, and family-specific isoform complexity. In addition, the exceptional diversity of NITR sequences among species suggests divergent evolution of this multigene family with a birth-and-death process of member genes. High-confidence modeling of Nitr V-domain structures reveals a significant shift in the spatial orientation of the Ig fold, in the region of highest interfamily variation, compared with Ig V domains. These studies resolve a complete immune gene cluster in zebrafish and indicate that the NITRs represent the most complex family of activating/inhibitory surface receptors thus far described.

SYNOPSIS. The prototypic forms of teleost novel immune-type receptors (NITRs) consist of a variable (V) region, a unique V-like C2 (V/C2) domain, a transmembrane region and a cytoplasmic tail containing immunoreceptor tyrosine-based inhibition motifs (ITIMs). NITRs encode diversified V regions in large multigene families but do not undergo somatic rearrangement. Studies in four different bony fish model systems have identified a number of different organizational forms of NITRs. Specifically,NITR genes encode Nterminal ectodomains of the V-type but otherwise vary in the: total number of extracellular immunoglobulin domains, number and location of joining (J) region-like motifs, presence of transmembrane regions, presence of charged residues within transmembrane regions, presence of cytoplasmic tails, and/or distribution of ITIM(s) within the cytoplasmic tails. V region-containing NITRs constitute a far more complex family than recognized originally and currently include individual members that potentially function through inhibitory as well as activating mechanisms. The genomic organization of the NITR gene cluster as well as the structural diversity and overall architecture of the NITR proteins is reminiscent of genes encoded at the mammalian leukocyte receptor cluster (LRC); however, there presently is no functional evidence to support an orthologous relationship between NITR and LRC gene products. Comparisons of the predicted structures of the NITRs have identified several short regions of sequence identity and a novel cloning strategy has been devised that selects for secretory and transmembrane proteins that encode these short motifs. Using this approach, related genes termed immune-type receptors (ITRs) have been identified in cartilaginous fish. Taken together, these studies indicate that leukocyte regulatory receptors, including those that mediate natural killer function, might have emerged early in vertebrate evolution and that the NITR/ITR genes represent a new and potentially highly significant link between innate and adaptive immune responses.

Reported here are self-exchange reactions between iron 2,2'-bi(tetrahydro)pyrimidine (H(2)bip) complexes and between cobalt 2,2'-biimidazoline (H(2)bim) complexes. The (1)H NMR resonances of [Fe(II)(H(2)bip)(3)](2+) are broadened upon addition of [Fe(III)(H(2)bip)(3)](3+), indicating that electron self-exchange occurs with k(Fe,e)(-) = (1.1 +/- 0.2) x 10(5) M(-1) s(-1) at 298 K in CD(3)CN. Similar studies of [Fe(II)(H(2)bip)(3)](2+) plus [Fe(III)(Hbip)(H(2)bip)(2)](2+) indicate that hydrogen-atom self-exchange (proton-coupled electron transfer) occurs with k(Fe,H.) = (1.1 +/- 0.2) x 10(4) M(-1) s(-1) under the same conditions. Both self-exchange reactions are faster at lower temperatures, showing small negative enthalpies of activation: DeltaH++(e(-)) = -2.1 +/- 0.5 kcal mol(-1) (288-320 K) and DeltaH++(H.) = -1.5 +/- 0.5 kcal mol(-1) (260-300 K). This behavior is concluded to be due to the faster reaction of the low-spin states of the iron complexes, which are depopulated as the temperature is raised. Below about 290 K, rate constants for electron self-exchange show the more normal decrease with temperature. There is a modest kinetic isotope effect on H-atom self-exchange of 1.6 +/- 0.5 at 298 K that is close to that seen previously for the fully high-spin iron biimidazoline complexes.(12) The difference in the measured activation parameters, E(a)(D) - E(a)(H), is -1.2 +/- 0.8 kcal mol(-1), appears to be inconsistent with a semiclassical view of the isotope effect, and suggests extensive tunneling. Reactions of [Co(H(2)bim)(3)](2+)-d(24) with [Co(H(2)bim)(3)](3+) or [Co(Hbim)(H(2)bim)(2)](2+) occur with scrambling of ligands indicating inner-sphere processes. The self-exchange rate constant for outer-sphere electron transfer between [Co(H(2)bim)(3)](2+) and [Co(H(2)bim)(3)](3+) is estimated to be 10(-)(6) M(-1) s(-1) by application of the Marcus cross relation. Similar application of the cross relation to H-atom transfer reactions indicates that self-exchange between [Co(H(2)bim)(3)](2+) and [Co(Hbim)(H(2)bim)(2)](2+) is also slow,or =10(-3) M(-1) s(-1). The slow self-exchange rates for the cobalt complexes are apparently due to their interconverting high-spin [Co(II)(H(2)bim)(3)](2+) with low-spin Co(III) derivatives.

Novel immune-type receptor ( NITR) genes that encode two extracellular immunoglobulin domains and cytoplasmic immunoreceptor tyrosine-based inhibition motifs (ITIMs) have been described previously in three lineages of bony fish. In the current study, four ITIM-containing NITR cDNAs are identified in the rainbow trout ( Oncorhynchus mykiss), and their expression patterns and genomic complexity are characterized. The ITIM-containing NITR2 gene maps 1.3 cM from an ITIM-containing C-type lectin receptor ( TCL-2) on linkage group XXI. A comprehensive, phylogenetic analysis of NITRs from rainbow trout and three other major lineages of bony fish defines conserved families of NITRs and suggests an ancient lineage of distinct groups of genes. Several probable scenarios that explain the origins of variant forms of NITRs are described.

Two decades of research have established the zebrafish (Danio rerio) as a significant model system for studying vertebrate development and gene structure-function relationships. Recent advances in mutation screening, the creation of genomic resources, including the Zebrafish Genome Project and the development of efficient transgenesis procedures, make this model increasingly attractive for immunological study.

A novel gene, BIVM (for basic, immunoglobulin-like variable motif-containing), has been identified using an electronic search based on the conservation of short sequence motifs within the variable region of immunoglobulin (Ig) genes. BIVM maps to human chromosome 13q32-q33 and is predicted to encode a 503-amino-acid protein with a pI of 9.1. The 5' untranslated region of BIVM is encoded in two exons; the coding portion is encoded in nine exons. BIVM is tightly linked (41 bp) and in the opposite transcriptional orientation to MGC5302 (also known as KDEL1 and EP58) in human. The ubiquitous expression of BIVM in normal tissues and the presence of a 5' CpG island suggest that BIVM is a housekeeping gene. Characterization of BIVM in representative species demonstrates significant conservation throughout deuterostomes; no sequence with significant identity to BIVM has been detected in proteostomes. However, an unusual gene has been identified in the protozoan pathogen Giardia lamblia that is similar to the core sequence of BIVM, suggesting the possibility of a horizontal gene transfer.

Major histocompatibility complex (MHC) molecules play a central role in the immune response and in the recognition of non-self. Found in all jawed vertebrate species, including zebrafish and other teleosts, MHC genes are considered the most polymorphic of all genes. In this review we focus on the multi-faceted diversity of zebrafish MHC class I genes, which are classified into three sequence lineages: U, Z, and L. We examine the polygenic, polymorphic, and haplotypic diversity of the zebrafish MHC class I genes, discussing known and postulated functional differences between the different class I lineages. In addition, we provide the first comprehensive nomenclature for the L lineage genes in zebrafish, encompassing at least 15 genes, and characterize their sequence properties. Finally, we discuss how recent findings have shed new light on the remarkably diverse MHC loci of this species.