The dynamic structure of XXXX blastocyst coverings. II. Ultrastructural evidence for a role of the trophoblast in neozona formation.

@entity2085 @entity95 @entity3584 @entity3739
The neozona is the innermost layer of the complex blastocyst coverings of the @entity95 and is located between the mucoprotein layer and the trophoblast. As shown previously the neozona begins to replace the zona pellucida from the 4th day post coitum (d p.c.) on (Denker and Gerdes 1979). In the present study, @entity95 blastocyst coverings were checked for regional differences in their composition, comparing the embryonic and the abembryonic pole of the blastocyst, at 5 and 6 d p.c. These two stages were chosen because at 5 d p.c. a complete trophoblast layer is still present at both the @entity2085 (Rauber's layer) and the extraembryonic regions (mural and abembryonic pole trophoblast), whereas at 6 d p.c. Rauber's layer has largely degenerated. Correlation of regional differences in blastocyst coverings structure with presence or absence of an intact trophoblast is taken as suggestive evidence for a role of the trophoblast in the formation or the structural modification of blastocyst coverings components. Blastocysts of both stages were fixed in @entity3584 with and without @entity3739 red and processed for TEM. The neozona was found to be almost equally well developed in all regions at 5 d p.c. On contrast, at 6 d p.c. (Rauber's layer defective) the neozona is consistently found to be much thinner at the @entity2085 than in the extraembryonic regions where the trophoblast is still intact. This is the first report on regional differences of the structural composition of blastocyst covering within the same blastocyst.(ABSTRACT TRUNCATED AT 250 WORDS)
