Genetics; Germ Cells; Stem Cells; Developmental Biology; Caenorhabditis elegans
Stem Cell Center, Yale: Stem Cell Self-Renewal and Cell Symmetry
Germ cells are highly specialized cells with the unique responsibility of producing healthy offspring, thus ensuring the continuity of a species across generations. These cells guard their DNA very carefully to allow the production of sperm and eggs with the right number of chromosomes and no mutations. We wish to understand how germ cells protect their DNA, while turning different genes on and off at the right times to make functional sperm and eggs. To grasp the most important trends, we use global genomic technologies to investigate many genes simultaneously. We are studying germ cell regulation primarily using the model organism C. elegans, a nematode, because of the large number of germ cells it contains, and because of the many experimental advantages it offers. Because the genes in C. elegans are related to those in higher organisms, the results from our studies should help us to understand how germ cells function in humans as well.
Extensive Research DescriptionWe focus on the development of a single tissue, the germline, in the model organism C. elegans. This small nematode provides two key advantages: an excellent genetic system for understanding how cell fate is specified, and a completely sequenced and well-annotated genome. We use functional genomics tools to dissect the molecular mechanisms governing germ cell maintenance and differentiation in the model organism C. elegans. Conserved regulatory pathways, such as the Notch, Ras, and Retinoblastoma pathways, act to control proliferation and differentiation in these cells. The developing C. elegans germline requires tight spatial and temporal control of gene activity for proper formation. Epigenetic control of gene expression plays an important role in governing germ cell fate through the post-translational modification of histones and by RNAi-mediated post-transcriptional control. Projects in the lab investigate the mechanisms controlling germ cell specification in the early embryo, as well as the regulatory hierarchy controlling germline stem cells before and after differentiation into functional gametes.
Germline stem cells. Virtually all cells in C. elegans are born within a determinate lineage. The single exception is a pair of primordial germ cells, which divide an unspecified number of times to populate the gonad. These proliferative germ cells bear several hallmarks of stem cells: they require a niche in the distal end of the gonad for maintenance, they self-renew, and they retain totipotency, since they can generate every cell type of the subsequent generation. Their maintenance also requires Notch signaling. We have used a functional genomics approach to investigate the properties of germline stem cells in C. elegans, and identified a large set of genes expressed primarily in germline stem cells. Many of these genes encode proteins predicted to function in chromatin-binding and transcriptional regulation, in RNA binding and RNA regulation, and as stress-activated chaperones. Efforts are underway in the lab to analyze the function of these genes in germline stem cell proliferation.
Germ cell-specific organelles. In C. elegans, the germ line is set aside within the first few embryonic divisions. As each cell in the embryonic P lineage divides, it produces another P cell that retains germ cell characteristics, and a somatic cell that does not. Within four divisions, the P lineage is completely segregated from all somatic lineages. One feature that distinguishes germ cells from somatic cells is the presence of unique cytoplasmic, RNA-rich, granular organelles, whose exact function remains mysterious. In C. elegans, these organelles, called P granules, are provided maternally and segregate with the P lineage during the initial embryonic divisions. All germ cells born from the P lineage contain P granules (except mature sperm). Several protein components of P granules have been identified, but their contribution to P granule function and germline viability remains unclear. We have identified two novel, related proteins that localize exclusively to embyonic P granules. They are not found in other cell compartments or on P granules in larvae or adults. These genes are called meg-1 and meg-2 (maternal-effect germ cell-defective), and they are required for larval germ cell proliferation and normal P granule morphology. meg-1 has genetic interactions with core components of P granules that suggests that meg-1 and meg-2 are required to regulate certain aspects of P granule function in the early P blastomeres during the time that somatic and germ fates are intermingled. Current efforts in the lab are directed toward defining the exact function of MEG-1 and MEG-2 and dissecting how P granules affect transcript stability in the early embryo.
- Waters K, Yang AZ, Reinke V. Genome-wide analysis of germ cell proliferation in C.elegans identifies VRK-1 as a key regulator of CEP-1/p53. Dev Biol. 344: 1011-1025.
- Genome-wide identification of binding sites defines distinct functions for Caenorhabditis elegans PHA-4/FOXA in development and environmental response. Zhong M, Niu W, Lu ZJ, Sarov M, Murray JI, Janette J, Raha D, Sheaffer KL, Lam HY, Preston E, Slightham C, Hillier LW, Brock T, Agarwal A, Auerbach R, Hyman AA, Gerstein M, Mango SE, Kim SK, Waterston RH, Reinke V, Snyder M. Genome-wide identification of binding sites defines distinct functions for Caenorhabditis elegans PHA-4/FOXA in development and environmental response. PLoS Genet. 2010 Feb 19;6(2):e1000848
- Katz DJ, Edwards TM, Reinke V, Kelly WG. (2009) A C. elegans LSD1 demethylase contributes to germline immortality by reprogramming epigenetic memory. Cell 137: 308-320.
- Hillier LW, Reinke V, Green P, Hirst M, Marra MA, Waterston RH (2009) Massively parallel sequencing of the polyadenylated transcriptome of C. elegans. Genome Research 19: 657-666.
- Wang G, Reinke V. (2008) A C. elegans Piwi, PRG-1, regulates 21U-RNAs during spermatogenesis. Current Biology 18: 861-867.
- Leacock SW, Reinke V. (2008) MEG-1 and MEG-2 are embryo-specific P-granule components required for germline development in Caenorhabditis elegans. Genetics 178: 295-306.
- Kudron MM, Reinke V. (2008) C. elegans nucleostemin is required for larval growth and germline stem cell division. PLoS Genetics 4(8):e1000181
- Chi, W. and Reinke, V. (2006). Promotion of oogenesis and embryogenesis in the C. elegans gonad by EFL-1/DPL-1 (E2F) does not require LIN-35 (pRB). Development 133: 3147-3157.