Platform Session 10. Germ Cell Differentiation and Development II
Chair(s): Eppig, John1, 1 The Jackson Laboratory, Bar Harbor, ME, USA
Monday, July 25, 2005
2:00 PM–4:00 PM
Location: CCQ 205ABC
(80) INVOLVEMENT OF Smad PATHWAYS ON SEXUALLY DIMORPHIC DIFFERENTIATION OF PRIMORDIAL GERM CELLS.
Tomaszewski, Jessica1, Aardema, Jorie 1, Yao, Humphrey1, 1 University of Illinois at Urbana-Champaign, Urbana, IL
ABSTRACT- Primordial germ cells (PGCs) are the embryonic precursors for both male and female gametes. Formation, migration, and expansion of PGCs are similarly regulated by molecular mechanisms in embryos of both sexes. Sexually dimorphic differentiation of germ cells does not arise until the completion of sex determination of somatic cells. In mice, divergence of PGC development begins at embryonic day 13.5 (E13.5). In the male gonad, PGCs are sequestered in testis cords by Sertoli cells and arrest in G1 of mitosis until puberty. In contrast, in the female gonad, PGCs begin to enter the first meiosis at E13.5, then arrest in the prophase of first meiosis, and eventually differentiate into oogonia. Evidence indicates that PGCs are programmed to follow the ovarian pathway unless they are placed in the testicular environment, which produces a male-specific factor(s) to inhibit meiosis. Transforming growth factor (TGF) proteins such as activins and anti-Mullerian hormone (AMH) are produced only in Sertoli cells before PGC divergence. We therefore hypothesize that these TGF proteins are responsible for the inhibition of PGC meiosis in male gonads. We first cultured female gonads with AMH or activins and found that these testis-specific TGF proteins inhibited the normal progression of PGC meiosis in female gonads. We then examined whether downstream signaling components of the TGF pathway are activated in PGCs in a male-specific manner. Immunocytochemical analysis revealed that phosphorylated Smad 1, 5, & 8 (activated by AMH) and Smad 2 & 3 (activated by activins) were only present in nuclei of male, but not female, PGCs right before the onset of meiosis. These observations suggest that the divergence of PGC development is established by testis-specific activation of the TGF pathway. However, inactivation of either one of the activins did not alter the phosphorylated pattern of Smad proteins and PGC differentiation. Multiple or compensatory mechanisms induced by other TGF ligands, such as AMH, may be present to ensure the prevention of PGC meiosis in male gonads, and therefore, allow the establishment of dimorphic germ lines. (Supported by Howard Hughes Undergraduate Fellowship and NIH HD46861).
KEY WORDS: Primordial Germ Cell, Meiosis, Activins, Anti-Müllerian Hormone