Search

Abstract: Gene duplication is thought to facilitate increasing complexity in the evolution of life. The fate of most duplicated genes is nonfunctionalization: functional decay resulting from the accumulation of mutations. [...]

The fatty acid-binding protein (fabp) genes belong to the multigene family of intracellular lipid-binding proteins. To date, 12 different FABPs have been identified in vertebrate genomes. Owing to the teleost-specific genome duplication event, many fishes have duplicated copies of the fabp genes. Here, we identified and characterized the fabp genes of spotted green pufferfish (Tetraodon nigroviridis). Seven fabp genes were identified, out of which, two were retained in the pufferfish genome as duplicated copies. Each putative pufferfish Fabp protein shares greatest sequence identity and similarity with their teleost and tetrapod orthologs, and clustered together as a distinct clade in phylogenetic analysis. Conserved gene synteny was evident between the pufferfish fabp genes and the orthologs of human, zebrafish, three-spined stickleback, and medaka FABP/fabp genes, providing evidence that the duplicated copies of pufferfish fabp genes most likely arose as a result of the teleost- specific genome duplication event. The differential tissue-specific distribution of pufferfish fabp transcripts suggests divergent spatial regulation of duplicated pairs of fabp genes. Key words: spotted green pufferfish, fatty acid-binding protein, teleost-specific genome duplication. Les genes codant pour des proteines de liaison aux acides gras (fabp) appartiennent a une famille multigenique de proteines intracellulaires de liaison des lipides. A ce jour, 12 FABP differents ont ete identifies au sein des genomes de vertebres. En raison de l'evenement de duplication genomique specifique des teleosteens, plusieurs poissons ont des copies dupliquees des genes fabp. Dans ce travail, les auteurs identifient et caracterisent les genes fabp chez le tetraodon vert (Tetraodon nigroviridis). Sept genes fapb ont ete identifies, dont deux representent des copies dupliquees qui ont ete conservees au sein du genome du tetraodon. Chaque proteine Fabp putative chez le tetraodon presente une identite et une similarite maximale avec son orthologue chez les teleosteens et les tetrapodes, de maniere a former un clade distinct en analyse phylogenetique. Une syntenie genique etait evidente entre les genes fabp du tetraodon et leurs orthologues chez l'humain, le poisson zebre, l'epinoche a trois epines et le medaka, ce qui suggere que les copies dupliquees des genes FABP/fabp chez le tetraodon sont vraisemblablement le resultat de l'evenement de duplication genomique specifique des teleosteens. La distribution tissus-specifique differentielle des transcrits fabp suggere une regulation spatiale divergente des paires de genes fabp dupliques. [Traduit par la Redaction] Mots-cles: tetraodon vert, proteine de liaison des acides gras, duplication genomique specifique des teleosteens., Introduction The members of the family of intracellular lipid-binding proteins (iLBP) are known to play vital roles in the transport of hydrophobic ligands such as long-chain fatty acids and retinoid [...]

A whole-genome duplication (WGD) early in the teleost fish lineage makes fish ideal organisms to study the fate of duplicated genes and underlying evolutionary trajectories that have led to the retention of ohnologous gene duplicates in fish genomes. Here, we compare the genomic organization and tissue-specific transcription of the ohnologous fabp7 and fabp10 genes in medaka, three-spined stickleback, and spotted green pufferish to the well-studied duplicated fabp7 and Fabp10 genes of zebrafish. Teleost fabp7 and fabp10 genes contain four exons interrupted by three introns. Polypeptide sequences of Fabp7 and Fabp10 show the highest sequence identity and similarity with their orthologs from vertebrates. Orthology was evident as the ohnologous Fabp7 and Fabp10 polypeptides of teleost fishes each formed distinct clades and clustered together with their orthologs from other vertebrates in a phylogenetic tree. Furthermore, ohnologous teleost fabp7 and fabp10 genes exhibit conserved gene synteny with human FABP7 and chicken FABP10, respectively, which provides compelling evidence that the duplicated fabp7 and fabp10 genes of teleost fishes most likely arose from the well-documented WGD. The tissue-specific distribution of fabp7a, fabp7b, fabp10a, and fabp10b transcripts provides evidence of diverged spatial transcriptional regulation between ohnologous gene duplicates of fabp7 and fabp10 in teleost fishes. Keywords: ohnologs, fabp7, fabp10, teleost, whole-genome duplication. Une duplication du genome entier qui s'est produite tot dans l'evolution des poissons teleosteens fait des poissons des organismes ideaux pour etudier le sort des genes dupliques et les trajectoires evolutives qui ont mene a la retention de ces genes dupliques, les ohnologues, au sein des genomes des poissons. Dans ce travail, les auteurs ont compare l'organisation genomique et le profil de transcription tissulaire des genes ohnologues fabp7 etfabp10 chez le medaka, l'epinoche a trois epines et le Tetraodon simulans a ceux rapportes pour leurs homologues largement etudies chez le poisson zebre, fabp7 etfabp10. Les genes fabp7 etfabp10 chez les teleosteens comptent quatre exons interrompus par trois introns. Les sequences proteiques de Fabp7 et de Fabp10 presentent les plus fortes identite et similarite de sequence avec leurs orthologues chez les vertebres. L'orthologie etait evidente chez les proteines ohnologues Fabp7 et Fabp10 des teleosteens, lesquelles formaient des clades distincts et etaient groupees avec leurs orthologues des autres vertebres au sein d'un arbre phylogenetique. De plus, les ohnologues fabp7 et fabp10 teleosteens presentaient respectivement une syntenie genique conservee avec les genes FABP7 humain et FABP10 du poulet, ce qui represente une preuve convaincante que les genes dupliques fabp7 et fabp10 des teleosteens seraient le fruit de la duplication genomique bien documentee. La repartition des transcrits fabp7a, fabp7b, fabp10a et fabp10b au sein des tissus fournit des evidences d'une regulation transcriptionnelle divergente entre ces genes dupliques ohnologues chez les teleosteens. [Traduit par la Redaction] Mots-cles: ohnologues, fabp7, fabp10, teleosteen, duplication du genome entier., Introduction Fatty acid binding proteins (FABPs) are abundant small intracellular proteins found in many tissues of vertebrates (Ockner et al. 1972; Veerkamp and Maatman 1995; Bernlohr et al. 1997). FABPs [...]

Here we describe the evolutionary relationship of the duplicated intestinal fatty acid binding protein genes fabp2a and fabp2b from medaka and three-spined stickleback by comparing them to the well-studied fabp2 gene from zebrafish. The duplicated fabp2 genes from medaka and three-spined stickleback consist of four exons separated by three introns, which code for a polypeptide of 132 amino acids. Fabp2a and Fabp2b of medaka and three-spined stickleback share highest sequence identity with zebrafish Fabp2. All Fabp2/FABP2 sequences from vertebrates form a distinct clade in a neighbor-joining phylogenetic tree with a robust 100% bootstrap value, which indicates that the medaka and three-spined stickleback fabp2a and fabp2b are orthologs of zebrafish fabp2. The syntenic genes of fabp2a and fabp2b from medaka and three-spined stickleback were shown to be conserved with the syntenic genes of fabp2/FABP2 from zebrafish and human, evidence that the duplicated fabp2 genes from medaka and three-spined stickleback most likely arose from the teleost-specific whole-genome duplication. The tissue- specific distribution of medaka and three-spined stickleback fabp2a and fabp2b transcripts, and zebrafish fabp2 transcripts, assayed by RT-qPCR suggests the acquisition of new function(s) by the medaka fabp2a, and the distinct evolution of fabp2b compared with fabp2a in the medaka and three-spined stickleback genomes. Key words: fabp2, medaka, three-spined stickleback, teleost, whole-genome duplication. Dans ce travail, les auteurs decrivent les relations evolutives de genes dupliques codant pour des proteines intestinales de liaison aux acides gras fabp2a etfabp2b chez le medaka et l'epinoche en les comparant au gene fabp2 bien etudie chez le poisson zebre. Les genes fabp2 dupliques chez le medaka et l'epinoche comptent quatre exons separes par trois introns et ils codent pour un polypeptide de 132 acides amines. Fabp2a et Fabp2b du medaka et de l'epinoche presentent la plus grande similarite de sequence avec Fabp2 du poisson zebre. Toutes les sequences Fabp2/FABP2 chez d'autres vertebres forment un clade distinct au sein des arbres phylogenetiques obtenus lors d'une analyse neighbor-joining avec une valeur de re-echantillonnage de 100%, ce qui indique que les genes fabp2a et fabp2b du medaka et de l'epinoche sont les orthologues de fabp2 du poisson zebre. Les genes synteniques avec fabp2a et fabp2b chez le medaka et l'epinoche sont conserves avec les genes synteniques avec fabp2/FABP2 chez le poisson zebre et l'humain, ce qui suggere que les genes fabp2 dupliques chez le medaka et l'epinoche seraient vraisemblablement le produit d'une duplication genomique specifique des teleosteens. L'analyse de l'expression tissulaire des genes fabp2a et fabp2b du medaka et de l'epinoche ainsi que fabp2 du poisson zebre, tel que mesuree par RT-qPCR, suggere l'acquisition de nouvelle(s) fonction(s) pour le gene fabp2a du medaka et une evolution distincte du gene fabp2b par rapport a fabp2a au sein des genomes du medaka et de l'epinoche. [Traduit par la Redaction] Mots-cles: fabp2, medaka, epinoche, teleosteen, duplication genomique., Introduction Fatty acids are an important source of energy in almost all vertebrates (EFSA Panel on Dietetic Products, Nutrition, and Allergies 2010). Owing to the hydrophobicity of fatty acids, they [...]

We describe a fatty acid-binding protein 1 (fabp1b.2) gene and its tissue-specific expression in zebrafish embryos and adults. The 3.5 kb zebrafish fabp1b.2 gene is the paralog of the previously described zebrafish fabp1a and fabp1b genes. Using the LN54 radiation hybrid mapping panel, we assigned the zebrafish fabp1b.2 gene to linkage group 8, the same linkage group to which fabp1b.1 was mapped. fabp1b.1 and fabp1b.2 appear to have arisen by a tandem duplication event. Whole-mount in situ hybridization of a riboprobe to embryos and larvae detected fabp1b.2 transcripts in the diencephalon and as spots in the periphery of the yolk sac. In adult zebrafish, in situ hybridization revealed fabp1b.2 transcripts in the anterior intestine and skin, and reverse transcription PCR (RT-PCR) detected fabp1b.2 transcripts in the intestine, brain, heart, ovary, skin, and eye. By contrast, fabp1b.1 transcripts were detected by RT-PCR in the liver, intestine, heart, testis, ovary, and gills. The tissue-specific distribution of transcripts for the tandemly duplicated fabp1b.1 and fabp1b.2 genes in adult tissues and during development suggests that the duplicated fabp1b genes of zebrafish have acquired additional functions compared with the ancestral fabp1 gene, i.e., by neofunctionalization. Furthermore, these functions were subsequently divided between fabp1b.1 and fabp1b.2 owing to subfunctionalization. Key words: whole genome duplication, Fabp1, L-Fabp, duplicated genes, tandem duplication, diencephalon, zebrafish. Les auteurs decrivent une proteine se liant aux acides gras (fabp1b.2) et son expression tissulaire chez les embryons et adultes du poison zebre. Le gene fabp1b.2 du poison zebre mesure 3,5 kb et il est le paralogue des genes fabp1a et fabp1b deja decrits. Au moyen du panel d'hybrides d'uradiation LN54, les auteurs ont assigne le gene fabp1b.2 au groupe de liaison 8, le meme groupe portant egalement fabp1b.1. fabp1b.1 et fabp1b.2 semblent provenir dune duplication en tandem. Des hybridations in situ au moyen dune sonde d'ARN marque sur des embryons et des larvas a detecte des transcrits de fabp1b.2 dans le diencephale et des signaux ponctuels dans la peripherie du sac vitellin. Chez les adultes, fhybridation in situ revele la presence de transcrits fabp1b.2 dans fintestin anterieur et la peau, et la RT-PCR detecte des transcrits fabp1b.2 dans fintestin, le cerveau, le coeur, l'ovaire, la peau et les yeux. Par ailleurs, des transcrits de fabp1b.1 ont ete detectes en RT-PCR dans le foie, fintestin, le coeur, les testicules, l'ovaire et les branchies. L'expression tissulaire specifique des genes dupliques en tandem fabp1b.1 et fabp1b.2 au sein des tissus adultes et au tours du developpement suggere que ces genes dupliques auraient acquis des fonctions additionnelles par rapport au gene ancestral fabp1, c'est-adire par neo-fonctionnalisation. De plus, ces fonctions auraient ensuite ete partagees entre fabp1b.1 et fabp1b.2 par voie de sub-fonctionnalisation. Mots-cles : duplication genomique, Fabp1, L-Fabp, genes dupliques, duplication en tandem, diencephale, poison zebre. [Traduit par la Redaction], Introduction Fatty acid-binding proteins (FABPs), members of the multigene family of intracellular lipid-binding proteins (iLBPs), are involved in the intracellular trafficking and se questering of fatty acids (Bernlohr et al. [...]

Abstract Background Force, Lynch and Conery proposed the duplication-degeneration-complementation (DDC) model in which partitioning of ancestral functions (subfunctionalization) and acquisition of novel functions (neofunctionalization) were the two primary mechanisms for the retention of duplicated genes. The DDC model was tested by analyzing the transcriptional induction of the duplicated fatty acid-binding protein (fabp) genes by clofibrate in zebrafish. Clofibrate is a specific ligand of the peroxisome proliferator-activated receptor (PPAR); it activates PPAR which then binds to a peroxisome proliferator response element (PPRE) to induce the transcriptional initiation of genes primarily involved in lipid homeostasis. Zebrafish was chosen as our model organism as it has many duplicated genes owing to a whole genome duplication (WGD) event that occurred ~230-400 million years ago in the teleost fish lineage. We assayed the steady-state levels of fabp mRNA and heterogeneous nuclear RNA (hnRNA) transcripts in liver, intestine, muscle, brain and heart for four sets of duplicated fabp genes, fabp1a/fabp1b.1/fabp1b.2, fabp7a/fabp7b, fabp10a/fabp10b and fabp11a/fabp11b in zebrafish fed different concentrations of clofibrate. Result Electron microscopy showed an increase in the number of peroxisomes and mitochondria in liver and heart, respectively, in zebrafish fed clofibrate. Clofibrate also increased the steady-state level of acox1 mRNA and hnRNA transcripts in different tissues, a gene with a functional PPRE. These results demonstrate that zebrafish is responsive to clofibrate, unlike some other fishes. The levels of fabp mRNA and hnRNA transcripts for the four sets of duplicated fabp genes was determined by reverse transcription, quantitative polymerase chain reaction (RT-qPCR). The level of hnRNA coded by a gene is an indirect estimate of the rate of transcriptional initiation of that gene. Clofibrate increased the steady-state level of fabp mRNAs and hnRNAs for both the duplicated copies of fabp1a/fabp1b.1, and fabp7a/fabp7b, but in different tissues. Clofibrate also increased the steady-state level of fabp10a and fabp11a mRNAs and hnRNAs in liver, but not for fabp10b and fabp11b. Conclusion Some duplicated fabp genes have, most likely, retained PPREs, but induction by clofibrate is over-ridden by an, as yet, unknown tissue-specific mechanism(s). Regardless of the tissue-specific mechanism(s), transcriptional control of duplicated zebrafish fabp genes by clofibrate has markedly diverged since the WGD event.

Abstract Background In the Duplication-Degeneration-Complementation (DDC) model, subfunctionalization and neofunctionalization have been proposed as important processes driving the retention of duplicated genes in the genome. These processes are thought to occur by gain or loss of regulatory elements in the promoters of duplicated genes. We tested the DDC model by determining the transcriptional induction of fatty acid-binding proteins (Fabps) genes by dietary fatty acids (FAs) in zebrafish. We chose zebrafish for this study for two reasons: extensive bioinformatics resources are available for zebrafish at zfin.org and zebrafish contains many duplicated genes owing to a whole genome duplication event that occurred early in the ray-finned fish lineage approximately 230-400 million years ago. Adult zebrafish were fed diets containing either fish oil (12% lipid, rich in highly unsaturated fatty acid), sunflower oil (12% lipid, rich in linoleic acid), linseed oil (12% lipid, rich in linolenic acid), or low fat (4% lipid, low fat diet) for 10 weeks. FA profiles and the steady-state levels of fabp mRNA and heterogeneous nuclear RNA in intestine, liver, muscle and brain of zebrafish were determined. Result FA profiles assayed by gas chromatography differed in the intestine, brain, muscle and liver depending on diet. The steady-state level of mRNA for three sets of duplicated genes, fabp1a/fabp1b.1/fabp1b.2, fabp7a/fabp7b, and fabp11a/fabp11b, was determined by reverse transcription, quantitative polymerase chain reaction (RT-qPCR). In brain, the steady-state level of fabp7b mRNAs was induced in fish fed the linoleic acid-rich diet; in intestine, the transcript level of fabp1b.1 and fabp7b were elevated in fish fed the linolenic acid-rich diet; in liver, the level of fabp7a mRNAs was elevated in fish fed the low fat diet; and in muscle, the level of fabp7a and fabp11a mRNAs were elevated in fish fed the linolenic acid-rich or the low fat diets. In all cases, induction of the steady-state level of fabp mRNAs by dietary FAs correlated with induced levels of hnRNA for a given fabp gene. As such, up-regulation of the steady-state level of fabp mRNAs by FAs occurred at the level of initiation of transcription. None of the sister duplicates of these fabp genes exhibited an increase in their steady-state transcript levels in a specific tissue following feeding zebrafish any of the four experimental diets. Conclusion Differential induction of only one of the sister pair of duplicated fabp genes by FAs provides evidence to support the DDC model for retention of duplicated genes in the zebrafish genome by either subfunctionalization or neofunctionalization.

When talkers anticipate that a listener may have difficulty understanding their speech, they adopt a speaking style typically described as "clear speech." This speaking style includes a variety of acoustic modifications and has perceptual benefits for listeners. In the present study, we examine whether clear speaking styles also include modulation of lexical items selected and produced during naturalistic conversations. Our results demonstrate that talkers do, indeed, modulate their lexical selection, as measured by a variety of lexical diversity and lexical sophistication indices. Further, the results demonstrate that clear speech is not a monolithic construct. Talkers modulate their speech differently depending on the communication situation. We suggest that clear speech should be conceptualized as a set of speaking styles, in which talkers take the listener and communication situation into consideration. [ABSTRACT FROM AUTHOR]

Background: In the duplication-degeneration-complementation (DDC) model, a duplicated gene has three possible fates: it may lose functionality through the accumulation of mutations (nonfunctionalization), acquire a new function (neofunctionalization), or each duplicate gene may retain a subset of functions of the ancestral gene (subfunctionalization). The role that promoter evolution plays in retention of duplicated genes in eukaryotic genomes is not well understood. Fatty acid-binding proteins (Fabp) belong to a multigene family that are highly conserved in sequence and function, but differ in their gene regulation, suggesting selective pressure is exerted via regulatory elements in the promoter. Results: In this study, we describe the PPAR regulation of zebrafish fabp1 a, fabp1 b.1, and fabp1 b.2 promoters and compare them to the PPAR regulation of the spotted gar fabp1 promoter, representative of the ancestral fabp1 gene. Evolution of the fabp1 promoter was inferred by sequence analysis, and differential PPAR-agonist activation of fabp1 promoter activity in zebrafish liver and intestine explant cells, and in HEK293A cells transiently transfected with wild-type and mutated fabp 1promoter-reporter gene constructs. The promoter activity of spotted gar fabp1, representative of the ancestral fabp1, was induced by both PPARa- and PPARy-specific agonists, but displayed a biphasic response to PPARa activation. Zebrafish fabp1a was PPARa-selective, fabp1b.1 was PPARy-selective, and fabp1 b.2 was not regulated by PPAR. Conclusions: The zebrafish fabp1 promoters underwent two successive rounds of subfunctionalization with respect to PPAR regulation leading to retention of three zebrafish fabp1 genes with stimuli-specific regulation. Using a pharmacological approach, we demonstrated here the divergent regulation of the zebrafish fabp1a, fabp1b.1, and fabp1 b.2 with regard to subfunctionalization of PPAR regulation following two rounds of gene duplication. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we examined the evolutionary trajectories and the common ancestor of medaka rbp genes by comparing them to the well-studied rbp/RBP genes from zebrafish and other vertebrates. We describe here gene structure, sequence identity, phylogenetic analysis and conserved gene synteny of medaka rbp genes and their putative proteins as well as the tissue-specific distribution of rbp transcripts in adult medaka and zebrafish. Medaka rbp genes consist of four exons separated by three introns that encode putative polypeptides of 134–138 amino acids, a genomic organization characteristic of rbp genes. Medaka Rbp sequences share highest sequence identity and similarity with their orthologs in vertebrates, and form a distinct clade with them in phylogenetic analysis. Conserved gene synteny was evident among medaka, zebrafish and human rbp/RBP genes, which provides compelling evidence that the medaka rbp1, rbp2a, rbp2b, rbp5, rbp7a and rbp7b genes arose from a common ancestor of vertebrates. Moreover, the duplicated rbp2 and rbp7 genes most likely exist owing to a whole-genome duplication (WGD) event specific to the teleost fish lineage. Selection pressure and the nonparametric relative rate test of the medaka and zebrafish duplicated rbp2 and rbp7 genes suggest that these duplicated genes are subjected to purifying selection and one paralog might have evolved at an accelerated rate compared to its sister duplicate since the WGD. The steady-state levels of medaka and zebrafish rbp1, rbp2a, rbp2b and rbp5 transcripts in various tissues suggest that medaka rbp1, rbp2a and rbp2b genes have retained the regulatory elements of an ancestral RBP1 and RBP2 genes, and the medaka rbp5 gene has acquired new function. Furthermore, the tissue-specific regulations of rbp7a and rbp7b genes have diverged markedly in medaka and zebrafish since the teleost-specific WGD. [Copyright &y& Elsevier]

Teleost fishes differ from mammals in their fat deposition and distribution. The gene for adipocyte-type fatty acid-binding protein (A-FABP or FABP4) has not been identified thus far in fishes. We have determined the cDNA sequence and defined the structure of a fatty acid-binding protein gene (designated fabp4) from the zebrafish genome. The polypeptide sequence encoded by zebrafish fabp4 showed highest identity to the Had-FABP or H6-FABP from Antarctic fishes and the putative orthologs from other teleost fishes (83–88%). Phylogenetic analysis clustered the zebrafish FABP4 with all Antarctic fish H6-FABPs and putative FABP4s from other fishes in a single clade, and then with the mammalian FABP4s in an extended clade. Zebrafish fabp4 was assigned to linkage group 19 at a distinct locus from fabp3. A number of closely linked syntenic genes surrounding the zebrafish fabp4 locus were found to be conserved with human FABP4. The zebrafish fabp4 transcripts showed sequential distribution in the developing eye, diencephalon and brain vascular system, from the middle somitogenesis stage to 48 h postfertilization, whereas fabp3 mRNA was located widely in the embryonic and/or larval central nervous system, retina, myotomes, pancreas and liver from middle somitogenesis to 5 days postfertilization. Differentiation in developmental regulation of zebrafish fabp4 and fabp3 gene transcription suggests distinct functions for these two paralogous genes in vertebrate development. [ABSTRACT FROM AUTHOR]

Abstract: The catalytic asymmetric rearrangement of functionalised cyclohexene and cyclopentene oxides has been studied using sub-stoichiometric amounts of a chiral lithium amide in combination with a stoichiometric amount of three different lithiated imidazoles. 1-Methylimidazole that had been lithiated at the C-2 aryl position gave the highest enantioselectivity (82% ee). With 1,2-dimethylimidazole that had been lithiated at the C-2 methyl group, epoxide ring opening occurred as an unexpected and competing process. Ultimately, ring opening was suppressed using a more sterically hindered imidazole. In all catalytic examples, a racemic background reaction (presumably due to rearrangement by the lithiated imidazoles) was observed. [Copyright &y& Elsevier]

The cellular retinoic acid-binding protein type I (CRABPI) is encoded by a single gene in mammals. We have characterized two crabp1 genes in zebrafish, designated crabp1a and crabp1b. These two crabp1 genes share the same gene structure as the mammalian CRABP1 genes and encode proteins that show the highest amino acid sequence identity to mammalian CRABPIs. The zebrafish crabp1a and crabp1b were assigned to linkage groups 25 and 7, respectively. Both linkage groups show conserved syntenies to a segment of the human chromosome 15 harboring the CRABP1 locus. Phylogenetic analysis suggests that the zebrafish crabp1a and crabp1b are orthologs of the mammalian CRABP1 genes that likely arose from a teleost fish lineage-specific genome duplication. Embryonic whole mount in situ hybridization detected zebrafish crabp1b transcripts in the posterior hindbrain and spinal cord from early stages of embryogenesis. crabp1a mRNA was detected in the forebrain and midbrain at later developmental stages. In adult zebrafish, crabp1a mRNA was localized to the optic tectum, whereas crabp1b mRNA was detected in several tissues by RT-PCR but not by tissue section in situ hybridization. The differential and complementary expression patterns of the zebrafish crabp1a and crabp1b genes imply that subfunctionalization may be the mechanism for the retention of both crabp1 duplicated genes in the zebrafish genome. [ABSTRACT FROM AUTHOR]