Search

Stem cell niches provide resident stem cells with signals that specify their identity. Niche signals act over a short range such that only stem cells but not their differentiating progeny receive the self-renewing signals (1). However, the cellular mechanisms that limit niche signalling to stem cells remain poorly understood. Here we show that the Drosophila male germline stem cells form previously unrecognized structures, microtubule-based nanotubes, which extend into the hub, a major niche component. Microtubule-based nanotubes are observed specifically within germline stem cell populations, and require intraflagellar transport proteins for their formation. The bone morphogenetic protein (BMP) receptor Tkv localizes to microtubule-based nanotubes. Perturbation of microtubule-based nanotubes compromises activation of Dpp signalling within germline stem cells, leading to germline stem cell loss. Moreover, Dpp ligand and Tkv receptor interaction is necessary and sufficient for microtubule-based nanotube formation. We propose that microtubule-based nanotubes provide a novel mechanism for selective receptor-ligand interaction, contributing to the short-range nature of niche-stem-cell signalling., The Drosophila testis represents an excellent model system to study niche-stem-cell interactions because of its well-defined anatomy: eight to ten germline stem cells (GSCs) are attached to a cluster of [...]

Although differential transcription drives the development of multicellular organisms, the ultimate readout of a protein-coding gene is ribosome-dependent mRNA translation. Ribosomes were once thought of as uniform molecular machines, but emerging evidence indicates that the complexity and diversity of ribosome biogenesis and function should be given a fresh look in the context of development. This Review begins with a discussion of different developmental disorders that have been linked with perturbations in ribosome production and function. We then highlight recent studies that reveal how different cells and tissues exhibit variable levels of ribosome production and protein synthesis, and how changes in protein synthesis capacity can influence specific cell fate decisions. We finish by touching upon ribosome heterogeneity in stress responses and development. These discussions highlight the importance of considering both ribosome levels and functional specialization in the context of development and disease. [ABSTRACT FROM AUTHOR]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2008.02.009 Byline: Daniel V. Lighthouse, Michael Buszczak, Allan C. Spradling Keywords: Drosophila; Fusome; Stem cell; Rab11 Abstract: The fusome plays an essential role in prefollicular germ cell development within insects such as Drosophila melanogaster. Alpha-spectrin and the adducin-like protein Hu-li tai shao (Hts) are required to maintain fusome integrity, synchronize asymmetric cystocyte mitoses, form interconnected 16-cell germline cysts, and specify the initial cell as the oocyte. By screening a library of protein trap lines, we identified 14 new fusome-enriched proteins, including many associated with its characteristic vesicles. Our studies reveal that fusomes change during development and contain recycling endosomal and lysosomal compartments in females but not males. A significant number of fusome components are dispensable, because genetic disruption of tropomodulin, ferritin-1 heavy chain, or scribble, does not alter fusome structure or female fertility. In contrast, rab11 is required to maintain the germline stem cells, and to maintain the vesicle content of the spectrosome, suggesting that the fusome mediates intercellular signals that depend on the recycling endosome. Author Affiliation: Howard Hughes Medical Institute Research Laboratories, Department of Embryology, Carnegie Institution, Baltimore, MD 21218, USA Article History: Received 18 December 2007; Accepted 2 February 2008

Metazoan physiology depends on intricate patterns of gene expression that remain poorly known. Using transposon mutagenesis in Drosophila, we constructed a library of 7404 protein trap and enhancer trap lines, the Carnegie collection, to facilitate gene expression mapping at single-cell resolution. By sequencing the genomic insertion sites, determining splicing patterns downstream of the enhanced green fluorescent protein (EGFP) exon, and analyzing expression patterns in the ovary and salivary gland, we found that 600-900 different genes are trapped in our collection. A core set of 244 lines trapped different identifiable protein isoforms, while insertions likely to act as GFP-enhancer traps were found in 256 additional genes. At least 8 novel genes were also identified. Our results demonstrate that the Carnegie collection will be useful as a discovery tool in diverse areas of cell and developmental biology and suggest new strategies for greatly increasing the coverage of the Drosophila proteome with protein trap insertions.

The use of fluorescent protein tags has had a huge impact on cell biological studies in virtually every experimental system. Incorporation of coding sequence for fluorescent proteins such as green fluorescent protein (GFP) into genes at their endogenous chromosomal position is especially useful for generating GFP-fusion proteins that provide accurate cellular and subcellular expression data. We tested modifications of a transposon-based protein trap screening procedure in Drosophila to optimize the rate of recovering useful protein traps and their analysis. Transposons carrying the GFP-coding sequence flanked by splice acceptor and donor sequences were mobilized, and new insertions that resulted in production of GFP were captured using an automated embryo sorter. Individual stocks were established, GFP expression was analyzed during oogenesis, and insertion sites were determined by sequencing genomic DNA flanking the insertions, The resulting collection includes lines with protein traps in which GFP was spliced into mRNAs and embedded within endogenous proteins or enhancer traps in which GFP expression depended on splicing into transposon-derived RNA, We report a total of 335 genes associated with protein or enhancer traps and a web-accessible database for viewing molecular information and expression data for these genes.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.cell.2006.04.004 Byline: Michael Buszczak (1), Allan C. Spradling (1) Abstract: Stem cells encapsulate the fundamental problem of metazoan biology in miniature: How do cells establish and maintain their fates? Increasing evidence indicates that stem cell chromatin activates proliferation genes and represses differentiation genes. Understanding how these configurations are stabilized by Polycomb group proteins will advance our understanding of embryonic development, tissue homeostasis, regeneration, aging, and oncogenesis. Author Affiliation: (1) Howard Hughes Laboratories and Embryology Department, Carnegie Institution of Washington, 3520 San Martin Drive, Baltimore, MD 21218, USA

Cajal bodies (CBs) are nuclear organelles that are usually identified by the marker protein p80-coilin. Because no orthologue of coilin is known in Drosophila melanogaster, we identified D. melanogaster CBs using probes for other components that are relatively diagnostic for CBs in vertebrate cells. U85 small CB-specific RNA, U2 small nuclear RNA, the survival of motor neurons protein, and fibrillarin occur together in a nuclear body that is closely associated with the nucleolus. Based on its similarity to CBs in other organisms, we refer to this structure as the D. melanogaster CB. Surprisingly, the D. melanogaster U7 small nuclear RNP resides in a separate nuclear body, which we call the histone locus body (HLB). The HLB is invariably colocalized with the histone gene locus. Thus, canonical CB components are distributed into at least two nuclear bodies in D. melanogaster. The identification of these nuclear bodies now permits a broad range of questions to be asked about CB structure and function in a genetically tractable organism.

We have studied the in vivo function and tissue specificity of Dcas, the Drosophila ortholog of CAS, the importin [beta]-like export receptor for importin [alpha]. While dcas mRNA is specifically expressed in the embryonic central nervous system, Dcas protein is maternally supplied to all embryonic cells and its nuclear/cytoplasmic distribution varies in different tissues and times in development. Unexpectedly, hypomorphic alleles of dcas show specific transformations in mechano-sensory organ cell identity, characteristic of mutations that increase Notch signaling. Dcas is essential for efficient importin-[alpha]3 nuclear export in mechano-sensory cells and the surrounding epidermal cells and is indirectly required for the import of one component of the Notch pathway, but not others tested. We interpret the specificity of the dcas phenotype as indicating that one or more Notch signaling components are particularly sensitive to a disruption in nuclear protein import. We propose that mutations in house keeping genes often cause specific developmental phenotypes, such as those observed in many human genetic disorders. Key Words: Drosophila; dcas; CAS; Cse1p; importin alpha nuclear export; nucleocytoplasmic transport; mechano-sensory bristle development; peripheral nervous system.

During Drosophila oogenesis, defective or unwanted egg chambers are eliminated during mid-oogenesis by programmed cell death. In addition, final cytoplasm transport from nurse cells to the oocyte depends upon apoptosis of the nurse cells. To study the regulation of germline apoptosis, we analyzed the midway mutant, in which egg chambers undergo premature nurse cell death and degeneration. The midway gene encodes a protein similar to mammalian acyl coenzyme A: diacylglycerol acyltransferase (DGAT), which converts diacylglycerol (DAG) into triacylglycerol (TAG), midway mutant egg chambers contain severely reduced levels of neutral lipids in the germline. Expression of midway in insect cells results in high levels of DGAT activity in vitro. These results show that midway encodes a functional DGAT and that changes in acylglycerol lipid metabolism disrupt normal egg chamber development in Drosophila.

Emerging evidence suggests that ribosome heterogeneity may have important functional consequences in the translation of specific mRNAs within different cell types and under various conditions. Ribosome heterogeneity comes in many forms, including posttranslational modification of ribosome proteins (RPs), absence of specific RPs and inclusion of different RP paralogs. The Drosophila genome encodes two RpS5 paralogs: RpS5a and RpS5b. While RpS5a is ubiquitously expressed, RpS5b exhibits enriched expression in the reproductive system. Deletion of RpS5b results in female sterility marked by developmental arrest of egg chambers at stages 7-8, disruption of vitellogenesis and posterior follicle cell (PFC) hyperplasia. While transgenic rescue experiments suggest functional redundancy between RpS5a and RpS5b, molecular, biochemical and ribo-seq experiments indicate that RpS5b mutants display increased rRNA transcription and RP production, accompanied by increased protein synthesis. Loss of RpS5b results in microtubule-based defects and in mislocalization of Delta and Mindbomb1, leading to failure of Notch pathway activation in PFCs. Together, our results indicate that germ cell-specific expression of RpS5b promotes proper egg chamber development by ensuring the homeostasis of functional ribosomes. [ABSTRACT FROM AUTHOR]