A reinvestigation of the role of the grey crescent in axis formation in xenopus laevis.

Gravitationally induced displacements of the contents of the frog egg can predictably determine the orientation of the subsequent dorsal-ventral axis of the embryo, regardless of the original position of sperm entry or of the grey crescent. In certain conditions, these displacements in the egg can also lead to the formation of a second axis, that is, to twinning. The previously reported ability of grafts of grey crescent cortex to induce secondary axes in recipient eggs is interpreted here as an unrecognized twinning effect of gravity. Our results lead to question the classic interpretation of the grey crescent as a dorsal determinant in amphibian development.

Morphometric estimation of stromal edema during delayed implantation in the rat.

Morphometric methods were used at the light microscopic level to investigate the appearance of edema in the endometrial stroma of rats during estradiol-induced implantation after an experimental delay. Comparisons between blastocyst-free and blastocyst-containing sites were made at 18, 12, 16 and 24 h after injection of estradiol (h.a.e.). The development of stromal edema during implantation was found to be diphasic. First, during the initial 8--12 h.a.e., a generalized edema developed all along the uterine horns. Later, from 16 h.a.e. onwards, a local edema was present around the blastocysts. The Pontamine Blue Reaction (PBR) became visible between 20 and 24 h.a.e. The results indicate that the blastocyst is recognized by the stroma considerably before the PBR. The appearance of a local edema around the blastocysts before the PBR might be related to a slow increase in vascular permeability and/or to the increased stromal cell synthetic activity that is known to precede the PBR during early implantation.