Transcriptional Control of Germ Cell Differentiation in Drosophila

University Of Texas Southwestern Medical Center, Dallas TX

Investigators

Abstract

Abstract Specific Goals. Cell differentiation is often induced by intercellular signaling and the Drosophila germarium is a valuable model for studying the molecules and mechanisms that can control differentiation (Spradling et al., 2001). Continuous production of eggs is maintained by two stable populations of stem cells, the germline stem cells (GSCs) and the somatic cell stem cells (SSCs). An epithelium of somatic cells forms a small cone that encloses the GSCs and the germ cells of the developing cysts (Spradling et al., 2001). The significance of signaling between somatic and germline cells has been confirmed for many of the cell types in the germarium. Xie and Spradling (2000) have shown that GSCs reside in a niche or microenvironment that produces survival and differentiation factors to recruit and maintain GSCs. More recently, genetic evidence suggests that communication between somatic cells and the cystoblast are important for differentiation (Schulz et al., 2002). As paracrine signaling pathways frequently act by activating differentiation-inducing transcription pathways, studies of transcriptional control of germ cell differentiation from GSCs into cystoblasts and cystocytes are essential. Stonewall is a transcription factor with motifs indicative of chromatin remodeling functions and is required for oocyte differentiation (Clark and McKearin, 1996). New data, however, suggests that the protein acts much earlier during germ cell differentiation. Conserved motifs in Stwl suggest that the protein could regulate chromatin structure. Studies in recent years have linked cell-specific chromatin remodeling to activation of "gene suites" required for differentiation in mice and flies (Freiman et al., 2001; Jiang and White-Cooper, 2003; Verrijzer, 2001). Thus studies of the Stwl mechanism could reveal a new aspect of germ cell differentiation, introducing cell-specific chromatin remodeling as a critical component of the molecular changes that drive differentiation. Specific Aims of this proposal include: (1) Refine phenotypic characterization of stwl mutants in light of recognition of different temporal requirements, (2) Identify Stwl binding proteins that act in concert to execute transcriptional programs, (3) Expand the collection of stwl alleles to include new conditional and weak alleles for eventual use in modifier screens to identify stwl-dependent gene activities. Scientific Merit and Broader Impact. Stem cells are frequently, perhaps obligately, associated with stromal cells in cellular microenvironments, or niches, that support and direct stem cell function. Cell-cell signaling between the stromal and stem cells controls the transcriptional programs of stem cells and the differentiating daughter cells. Identifying the relevant transcription factors and their modes of action will greatly extend our understanding of niche formation, maintenance and function. While niche control of stem cells may occur widely in biology, it is very difficult to examine directly in most systems. Difficulty locating niches, small population sizes and a paucity of diagnostic cytological markers often prevent detailed studies. These problems can be overcome in Drosophila ovaries. Cross-phyla conservation of signaling pathways and the responding transcription factors argues strongly that related regulatory mechanisms will function in mammalian niches as well. The proposed studies will also offer impact beyond the scientific investigations as they will train new scientists in the skills essential for careers in science teaching, biotechnology discovery and company analysis as well as research practice. Literature Cited Clark, K. A. and McKearin, D. M. (1996). The Drosophila stonewall gene encodes a putative transcription factor essential for germ cell development. Development 122, 937-50. Freiman, R. N., Albright, S. R., Zheng, S., Sha, W. C., Hammer, R. E. and Tjian, R. (2001). Requirement of tissue-selective TBP-associated factor TAFII105 in ovarian development. Science 293, 2084-7. Jiang, J. and White-Cooper, H. (2003). Transcriptional activation in Drosophila spermatogenesis involves the mutually dependent function of aly and a novel meiotic arrest gene cookie monster. Development 130, 563-73. Schulz, C., Wood, C. G., Jones, D. L., Tazuke, S. I. and Fuller, M. T. (2002). Signaling from germ cells mediated by the rhomboid homolog stet organizes encapsulation by somatic support cells. Development 129, 4523-34. Spradling, A., Drummond-Barbosa, D. and Kai, T. (2001). Stem cells find their niche. Nature 414, 98-104. Verrijzer, C. P. (2001). Transcription factor IID--not so basal after all. Science 293, 2010