Absence of Live-Borns from XY Oocytes
Despite the fertility of all chimeric females, no live-boms were produced from XY oocytes. This observation suggests that the presence of XX cells failed to make the XY oocyte competent for reproduction. Therefore, the developmental failure of the XY oocyte is most likely intrinsic to the oocyte itself, and not to the surrounding somatic cells in the B6.YTIR ovary. Possible competition between the germ cells of two mouse strains in the chimera has been reported previously. Accordingly, it is conceivable that XY oocytes were excluded from the chimeric ovaries in competition with XX oocytes. In the present study, however, we confirmed the presence of XY oocytes at different stages of follicular development in XX BALB/c <-> XY B6.YTIR chimeric ovaries. It remains possible that XX oocytes were favorably recruited for ovulation and, therefore, the absence of progeny derived from XY oocytes may be attributable to the paucity of XY-derived eggs ovulated rather than death of XY-derived embryos. Nonetheless, it must be emphasized that the XY genotype of the oocyte, and not of somatic cells, appears to be responsible for exclusion of XY oocytes from the reproductive process, whether at ovulation or after fertilization. buy flovent inhaler
Unlike XX BALB/c XY B6.YTIR chimeric ovaries, both germ cell populations in the XY BALB/c <-4 XY B6.YTIR chimeric testis contributed to progeny production. Therefore, the absence of progeny derived from the XY oocyte is associated with the infertility of the B6.YTIR female, rather than the results of general competition between B6.YT1R and BALB/c germ cells. The BALB/c strain appeared to be favored over the B6.YT,R strain for young-born production if their proportions in the testis were parallel to those in the coat color. However, it is conceivable that extensive proliferation of spermatogonia may have distorted the proportion. A larger number of chimeric males is needed to determine whether the BALB/c genotype always has an advantage over the B6.YT,R genotype in spermatogenesis.