In vitro development of aggregate embryos obtained by pairing the microsurgically halved morulae of mice and rats, and observations on their aggregation process in scanning electrone and fluorescence microscopies.

Abstract

Using the halved morulae of rats and mice obtained with microsurgical technique, the following items were investigated:1) Production of aggregate embryos by the method of MINTZ1) and investigation on the subsequent development.2) Observation on aggregation and fusion of the paired demi-embryos by scanning elec-trone microscopy (SEM).3) Fluorescent vital staining (FITC & TRIT) of the paired demi-embryos and investga-tion on distribution of the dyes during development in the aggregate embryo in vitro.Out of 107 pairs of rat's demi-embryos, 87 were successfully aggregated, of which 63 (58%) developed to the blastocyst stage. While, 85 out of 127 pairs of mouse demi-embryos suc-cessfully aggregated, of which 71 (56%) developed to late morulae and 14 (11%) to blasto-cysts. These rat and mouse aggregate blastocysts were slightly small in size but were found to have inner cell masses.The observation by SEM revealed that the fused embryo at late morula stage had the structure of a linear sulcus running around the equatorial surface. The location of this sulcus seemed to be the border where the paired demi-embryos made contact to fuse each other.The distribution of the fluorescent dyes showed that two hemispherical cell masses with different colors made contact at the central plane of the morula, and that in the blastocyst the inner cell mass was also consisted of two cell populations with different colors confront-ing either vertically or horizontally.These observations suggested that two groups of cell mass might seldom mingle each other in the aggregate embryo during early developmental period until the blastocyst stage, thereafter two groups of blastomeres of different origin seem to begin mixing.