The Male Germline Stem Cell Niche
My lab focuses on how genetic and epigenetic modulators promote the development and maintenance of adult stem cells
Microenvironments, or niches, support the maintenance of stem cells and facilitate the development of tumors through largely unknown mechanisms. Cell-autonomous genetic pathways and epigenetic networks have emerged as important determinants for the self-renewal and differentiation of stem cells in embryonic, juvenile, and adult issues. The importance of non-cell autonomous genetic and epigenetic factors is less well established. Our goal is to identify and characterize the genetic and epigenetic mechanisms utilized by both stem cells and their surrounding niche in supporting the stem cell program. For these studies, the developing mouse testis is used to examine interactions between male germline stem cells (GSCs) and their somatic niche.
Within the testis, differentiated germ cells are continually replenished by self-renewing GSCs to ensure the continuation of spermatogenesis throughout the lifetime of the male. GSCs are adult stem cells that develop after birth, but which derive from embryonic primordial germ cells (PGCs). Under abnormal conditions, PGCs are thought to become pluripotent in vivo, develop into carcinoma in situ, and form post-pubertal testicular germ cell tumors, the most common cancer in men aged 15-40. When GSC differentiation occurs at the expense of self-renewal, depletion of germ cells and infertility can result.
Several candidate factors influencing GSC self-renewal and differentiation are being studied: chromatin remodeling gene Sin3a, Polycomb group member Ezh2, and a chemokine ligand and its receptor, Cxc112 and Cxcr4. Current research is examining the role of Sin3a in somatic Sertoli cells, which support GSCs and nurture all differentiating germ cells. Analysis of Ezh2 in GSCs as well as in testicular germ cell tumors is being conducted to determine whether an altered 'Polycomb repression signature' promotes germ cell tumorigenesis. Characterization of Cxc112, which is expressed in Sertoli cells, and Cxcr4, expressed in germ cells, is being performed to determine whether this chemokine signaling pathway is required to maintain GSCs in their niche, and whether this mechanism involves non-coding microRNAs.
To achieve these aims, distinct testicular cells populations are separated by fluorescence- and magnetic-activated cell sorting and analyzed by transcriptional profiling. Potential SIN3A and EZH2 complex-bound target genes are identified by chromatin immunoprecipitation. Loss-of-function effects are examined by one of two methods: generation of conditional knockout mice or RNAi knockdown and transplantation of cultured GSCs into recipient testes. Future studies are aimed at understanding how the niche maintains stem cells and ensures proper organogenesis, with the possibility of tissue regeneration and cancer prevention as therapeutic applications.
Payne, C.J., Gallagher, S.J., Foreman, O., Dannenberg, J.H., Depinho, R.A., Braun, R.E. (2010). Sin3a is required by Sertoli cells to establish a niche for undifferentiated spermatagonia, germ cell tumors, and spermatid elongation. Stem Cells 28:1424-1434.
Payne, C.J., and Braun, R.E. (2008). Human adult testis-derived pluripotent stem cells: revealing plasticity from the germline. Cell Stem Cell 3:471-472.
Sadate-Ngatchou, P.I., Payne, C.J., Dearth, A.T., and Braun, R.E. (2008). Cre recombinase activity specific to postnatal, premeiotic male germ cells in transgenic mice. genesis 46:738-742
Payne, C. and Braun, R.E. (2006). Glial cell line-derived neurotrophic factor maintains a POZ-itive influence on stem cells. Proc Natl Acad Sci. USA 103:9751-9752.
Payne, C. and Braun, R.E. (2006). Histone lysine trimethylation exhibits a distinct perinuclear distribution in Plzf-expressing spermatogonia. Dev Biol. 293:461-472.
Rawe, V.Y., Payne, C., and Schatten, G. (2006). Profilin and actin-related proteins regulate microfilament dynamics during early mammalian embryogenesis. Hum Reprod. 21:1143-1153.