The Direct Demonstration of an X-Chromosome Dosage Effect Prior to Inactivation
When the X-linked enzyme, hypoxanthine guanine phosphoribosyl-transferase (HGPRT), was found to increase significantly in activity during the morula stage of preimplantation mouse embryonic development (Epstein 1970), it was obvious that this enzyme would be a useful marker for studying the control of X-chromosome expression. This conviction was strengthened by the finding that, while still present at the 2-cell stage, the gene dosage effect related to the number of X chromosomes present during oogenesis is no longer present after blastulation, indicating that the increase in HGPRT activity is determined by the embryonic genome (Epstein 1972).
KeywordsDirect Demonstration Teratocarcinoma Cell Female Embryo Morula Stage Howard Hughes Medical Institute
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