APOPTOSIS IN MOUSE EMBRYOS - ELEVATED LEVELS IN PREGASTRULA AND IN THE DISTAL ANTERIOR REGION OF GASTRULA OF NORMAL AND MUTANT MICE

The pattern of apoptotic cell death has been surveyed in prestreak and primitive streak embryos of four strains of mice and in three mutants affecting gastrulation, In C57BL/6 embryos, a high level of cell deat h occurs in the early egg cylinder stage at embryonic day 5 (E5) to E5 .5. In all strains, cell death is elevated shortly before gastrulation , but the level varies four- to fivefold among strains, During gastrul ation, cell death declines but is relatively more abundant in the dist al and distal anterior regions. Early streak embryos cultured in media with reduced levels of growth factors show increased cell death mainl y in the distal region. In three mutants with disturbed function of th e proximal visceral endoderm and/or primitive streak, cell death is in creased, and the regional pattern seen in normal embryos is intensifie d. The results strongly suggest that the proximal visceral endoderm an d primitive streak region are the principal sites of synthesis of grow th factors promoting cell survival. We conclude that localized growth factor supply has an important role in regulating the size of the embr yo and of embryonic regions. Dev. Dyn. 1998;213:293-308, (C) 1998 Wile y-Liss, Inc.