Sex-related differences in the developmental rate of in-vitro matured/in-vitro fertilized ovine embryos

Abstract

Sex determination of in-vitro matured/in-vitro fertilized ovine embryos cultured in synthetic oviduct fluid (SOF) medium was performed by the polymerase chain reaction amplification of specific Y DNA sequences so as to test the influence of sex on developmental growth during the preimplantation period. At 144 h post-insemination, embryos with a blastocoel were classified as the fast-developing group, whereas those showing a blastocoel only after this length of time were classified as the slow-developing group. At 144 h post-insemination, fast-developing embryos were cultured separately and some were classified according to the size of their blastocoel. At the end of culture (207 h post-insemination), all embryos were classified according to both their developmental stage and their morphological quality. The male:female sex ratio of fast-developing embryos was significantly higher than the expected ratio of 50%. More males were observed at the most advanced developmental stage at both 144 and 207 h post-insemination. The proportion of males did not differ between the good- and poor-quality groups, although a skewed sex ratio was observed with embryos of better quality at the most developed stage. In conclusion, embryos at the most developed stage were predominantly male and were derived mainly from the fast-developing group, raising the possibility of a deviation in the sex ratio after the transfer of in-vitro matured/in-vitro fertilized ovine embryos.

Sexual dimorphism among bovine embryos in their ability to make the transition to expanded blastocyst and in the expression of the signaling molecule IFN-τ

“…Embryos produced in vitro in a number of species fall into fast-cleaving and slow-cleaving groups, which are predominantly male and female, respectively. This phenomenon has been observed for bovine (1)(2)(3)(4)(5),** mouse (6,7), sheep (8,9), and human embryos (10). In vivo-produced male pig embryos, both before and subsequent to hatching from the zona pellucida, have also been reported to be larger and to have more cells than female embryos (11,12).…”

Low O 2 tensions and the prevention of differentiation of hES cells

“…Moreover, anaerobic bacteria are able to colonize the uterine lumen (15,16). Embryos are exceedingly sensitive to oxidative damage (17)(18)(19)(20)(21)(22)(23)(24), and blastocysts produced under low O 2 have significantly more inner cell mass cells than those produced under higher O 2 tensions (25). Accordingly, embryologists generally culture embryos under a low rather than high oxygen atmosphere (17)(18)(19)(20)(21)(22).…”

Influence of embryo sex on development to the blastocyst stage and euploidy

“…One possible mechanism for an altered sex ratio is an increased developmental rate in male embryos. Multiple authors have demonstrated increased cellularity and shorter time to blastocoele formation in murine (14)(15)(16), bovine (17)(18)(19), ovine (20), and porcine (21) male embryos compared with female embryos. Proposed mechanisms include metabolic differences (22), Y-linked gene expression (15,23,24), and epigenetic effects (25).…”