TISSUE NONSPECIFIC ALKALINE-PHOSPHATASE IS EXPRESSED IN BOTH EMBRYONIC AND EXTRAEMBRYONIC LINEAGES DURING MOUSE EMBRYOGENESIS BUT IS NOT REQUIRED FOR MIGRATION OF PRIMORDIAL GERM-CELLS

Mouse primordial germ cells express tissue non-specific alkaline phosp hatase (TNAP) during development, but the widespread expression of ano ther alkaline phosphatase gene in the early embryo limits the potentia l use of this marker to trace germ cells. To attempt to identify germ cells at all stages during embryonic development and to understand the role of TNAP in germ cell ontogeny, mice carrying a beta geo (lacZ/ne o') disrupted allele of the TNAP gene were generated by homologous rec ombination in embryonic stem cells. Using beta-galactosidase activity, the embryonic pattern of TNAP expression was examined from the blasto cyst stage to embryonic day 14. Results indicate that primordial germ cell progenitors do not express TNAP prior to gastrulation although at earlier times TNAP expression is found in an extraembryonic lineage d estined to form the chorion. In homozygous mutants, primordial germ ce lls appear unaffected indicating that TNAP is not essential for their development or migration.