The albino deletion complex and early postimplantation survival in the mouse

The albino deletion complex in the mouse represents 37 overlapping chromosomal deficiencies that have been arranged into at least twelve complementation groups. Many of the deletions cover regions of chromosome 7 that contain genes necessary for early embryonic development. The work reported here concentrates on two of these deletions (c6H, c11DSD), both of which were known to be lethal around the time of gastrulation when homozygous. A detailed embryological analysis has revealed distinct differences in the lethal phenotype associated with the c6H and c11DSD deletions. c6H homozygous embryos are grossly abnormal at day 7.5 of gestation, whereas c11DSD homozygous embryos appear abnormal at day 8.5 of gestation. There is no development of the extraembryonic ectoderm in c6H homozygotes, whereas extensive development of this tissue type occurs in c11DSD homozygotes. The visceral endoderm is abnormally shaped and the parietal endoderm appears to be overproduced in c6H homozygotes; these structures are not affected in c11DSD homozygotes. The embryonic ectoderm is runted in both types of embryo and it is not possible to obtain homozygous embryo-derived stem-cell lines for either deletion. Mesoderm formation occurs in the c11DSD but not in the c6H homozygotes. The c11DSD deletion chromosome complements the c6H chromosome in that the lethal phenotype of the compound heterozygote is similar to that of the c11DSD homozygote. These results suggest that a gene(s) necessary for normal development of the extraembryonic ectoderm is present in the c11DSD but deficient in the c6H deletion chromosome.