Identification of a male‐specific histocompatibility protein on preimplantation porcine embryos

An indirect immunofluorescence assay was used to detect the presence of male‐specific protein(s) on various stages of preimplantation porcine embryos. Embryos were collected at slaughter from the reproductive tracts of day−2.5, −4, −5, −6, and −8 (day 0 = first day of estrus) sows and gilts. Embryos were placed in medium containing an anti‐male primary antibody, washed, and transferred to culture drops containing a fluorescein isothiocyanate (FITC)‐labeled secondary antibody. Embryos were classified as either fluorescent (H‐Y positive) or nonfluorescent (H‐Y negative), transferred to coded drops, and karyotyped to examine sex chromosomes. A total of 91 eight‐cell to blastocyst stage embryos were evaluated; of these, 46% were classified as fluorescent and 54% as nonfluorescent. Of readable metaphase spreads (65%) from these embryos, 81% (48 of 59, P < 0.005) were correctly sexed by immunological detection of the male‐specific antigen. Although 13 % (2/15)of four‐cell embryos evaluated were classified as fluorescent, the accuracy with which embryos at this stage were sexed by detection of H‐Y antigen was not different from 50%. Fifty percent of eight‐cell embryos were classified as H‐Y positive with 78% of embryos correctly sexed. It was concluded that the eight‐cell embryo is the earliest stage of development for which there is evidence for expression of H‐Y antigen. Detection of the male‐specific protein was difficult at the expanded blastocyst stage.