We identify genes essential for the development and function of male germ cells, determine the roles of their encoded proteins, and define the mechanisms regulating their functions. The major areas of research currently are the regulation of meiotic progression in spermatogenic cells, the role of peritubular myoid cells in regulating spermatogonial stem cell renewal in the testis stem cell niche, and the influence of genetic background on PRM2 gene expression.
The mechanisms regulating transition from prophase I to metaphase I of meiosis during spermatogenesis remain uncertain. CCNB1 and CDK1 form the ìmaturation-promoting factorî (MPF) complex, with CCNB1 serving as the primary regulator of the cyclin-dependent kinase activity of CDK1. To determine if the MPF has a direct role during meiosis in males, we created pachytene spermatocyte-specific conditional knock out lines for each of these genes. These studies have demonstrated that CDK1 is required for meiosis in male mice, CDK2 cannot form an active MPF by heterdimerizing with CCNB1 in the absence of CDK1, and CCNA1 may function in parallel with CDK1 in meiotic progression in the male. Studies are underway to determine the role of CCNB1 during this process.
Spermatogonial stem cells (SSC) sit at the periphery of the seminiferous tubule surrounded by Sertoli cells, peritubular myoid (PM) cells and the basement membrane of the tubule in a microenvironmental compartment referred to as the SSC niche. They divide and either remain as SSCs, or become type A spermatogonia to undergo multiple divisions and further differentiate sequentially into spermatocytes, spermatids and sperm. We isolated PM cells, grew them in culture and found that testosterone stimulates the production of GDNF and LIF by these cells. When SSCs were isolated and co-cultured with PM cells in the presence of testosterone they were competent to self-renew, differentiate and reestablish spermatogenesis after transplantation to the testis of germ-cell-depleted hosts. However, SSCs co-cultured with PM without testosterone produced few colonies after transplantation. These studies indicate that PM cells have an important role in regulating the microenvironment of the SSC niche.
Following meiosis in the male, the histones are removed and replaced by transition proteins and in turn by protamines, as the sperm nucleus becomes highly condensed. Abnormal protamine levels are associated with sperm DNA fragmentation and human infertility. To study this condition, we generated mice with one copy of either the Prm1 or Prm2 gene disrupted and found they were infertile due to haploinsufficiency and that embryonic development following ICSI was compromised, with most embryos dying by the blastocyst stage. However, we found that C57BL/6 male mice with one copy of the Prm2 gene disrupted were fertile, whereas 129S6 male mice with one copy of the Prm2 gene disrupted were infertile. We hypothesize that a modifier(s) of Prm2 gene expression is present in the 129S6 genome that is detrimental to male fertility. We performed an intercross experiment between C57BL/6 and 129S6 mice, determined male fertility in F2 offspring, and performed a QTL analysis to identified potential modifier genes. Significant QTLs were identified on chr4 and chr11 and current studies are refining the intervals with the goal of identifying the responsible modifier genes.
Edward M. (Mitch) Eddy received his B.S. and M.S. in Zoology from Kansas State University in 1964 and his Ph.D. in Anatomy from the University of Texas Medical Branch in 1967. He was a NIH Postdoctoral Fellow and an Instructor at Harvard Medical School before joining the faculty at the University of Washington School of Medicine, advancing to Professor in 1982. He came to the NIEHS in 1983 to lead the Gamete Biology Group in the Laboratory of Reproductive and Developmental Toxicology. He served as President of the Society for the Study of Reproduction in 2006 and has received several awards, including the Distinguished Andrologist award of the American Society of Andrology and the Distinguished Service Award of the Society for the Study of Reproduction.