Given the broad expression pattern of mbc , it was of interest to examine mbc mutant embryos for defects in other tissues.
Mutant embryos exhibit a severe somatic muscle phenotype.
However, these defects may be an indirect consequence of the lack of somatic muscles rather than a direct effect of the loss of Mbc in either the visceral mesoderm or the endoderm. Although no epidermal defects had been reported in mbc mutant embryos, the early expression of mbc in the ectoderm, which persists in the epidermis into stage 14, led to a reexamination of mbc mutant embryos for epidermal defects. The extent of completion of dorsal closure varies from a relatively small opening surrounded by puckered misshapen cells to a very large opening. In the normal course of dorsal closure in a wild-type embryo, the epidermal cells elongate, and the epithelium stretches over the entire circumference of the embryo. In the early stages of dorsal closure in mbc mutant embryos, the cells along the leading edge of the epidermis appear to be normal.