Ultrastructure of murine trisomy 1 optic cup

The optic cups of two gestational day 11 trisomy (ts) 1 mouse embryos and a normal littermate control were examined using transmission electron microscopy (TEM). One trisomic embryo had a small lens with a lens stalk; the other was aphakic. The resolution available with TEM allowed detailed evaluation of cell organelles, spatial relationships, and the intra- and extracellular structural environment of the optic cup in normal and abnormal mouse embryos. Differences between the normal littermate and the trisomic optic cups, as well as between the two ts 1 structures, included the following: 1) melanin granules in the retinal layer and intraretinal space as well as in the pigment layer, 2) neither pseudostratified nor cuboidal neuroepithelium in trisomic optic cups, 3) increasing cell lysis with severity of eye defect, 4) fusion between retinal and pigment layer cells and cells from the pigment layer and head mesoderm. This investigation not only confirmed some of the abnormal morphology found in light microscopic studies of ts 1 at this gestational age but also identified other anomalies in the ts 1 eye that may play a part in the dysgenesis of this organ. The roles of larger than normal intercellular lacunae, disorganized microtubules, and the connections between different cell types in the ts 1 optic cup require further investigation.