Measurement of HPRT activity in the human unfertilized oocyte and pre‐embryo

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Abstract
The hypoxanthine phosphoribosyl transferase (HPRT) and adenine phosphoribosyl transferase (APRT) activities in individual non-fertilized human eggs and in human pre-embryos (4-cell to blastocyst stage) have been analysed. A wide spread of activities was observed, the mean values of which decline with time post-ovulation for both eggs and advancing preembryonic stages. The variation in activities was less in groups of eggs or pre-embryos recovered from a single ovulatory cycle. The activity of HPRT, but not of APRT, was readily detectable in single 4-cell and 8-cell blastomeres. When pre-embryos at various preimplantation stages were exposed to α-amanitin, to block transcription of mRNA from the preembryonic genome, no clear effect on HPRT activity was observed. It is concluded that the HPRT and APRT activities measured in the pre-embryos studied here are likely to be maternally inherited, and that use of a direct assay for HPRT activity for the pre-implantation diagnosis of Lesch–Nyhan disease would be premature.