Preimplantation sexing and diagnosis of hypoxanthine phosphoribosyl transferase deficiency in mice by biochemical microassay.

Hypoxanthine phosphoribosyl transferase (HPRT)-deficient male embryos derived from heterozygous (carrier) female mice were diagnosed by biochemical microassay of X-chromosome-coded HPRT activity in a single cell taken from the 8-cell embryo or in 5-10 cells sampled from the blastocyst. In the latter procedure, carrier female blastocysts could also be distinguished from affected males, and normal males and females, as having intermediate HPRT activity in the sampled trophectoderm cells. During the assay procedures, the operated preimplantation embryos were cultured. They were then transferred, in batches as diagnosed, to recipient females. The resulting fetuses were sexed by gonad morphology and assayed for HPRT activity. All those identified as HPRT-negative embryos by biopsy at the 8-cell or blastocyst stages were indeed HPRT-negative males. The heterozygous females were also correctly identified by the trophectoderm biopsy procedure. The sex of an embryo can also be diagnosed by HPRT activity dosage in a single blastomere taken from 8-cell embryos from a normal mating and cultured for 12 hours before assay. Both X chromosomes are active in female morulae and the blastomeres sampled from female preimplantation embryos have twice the X-coded HPRT activity compared to those from the male embryos. The accuracy of this procedure for sexing was again verified by transfer of the putative male and putative female embryos into recipient females.