Embryogenesis of an embryonic lethal, ‘kidney-shaped egg’ in Bombyx mori, with special reference to mesoderm differentiation

Summary

Within the kidney-shaped egg laid by the homozygous female, the embryo develops only ectodermal organs, but no mesodermal organs. The early embryogenesis of this strain was examined with light and electron microscopy. Until the early germband stage no remarkable differences are distinguishable between the normal and the kidney-shaped eggs. Afterwards, in the kidney-shaped egg large amount of cytoplasmic masses and often several cells are extruded from the presumptive head region into the yolk at the ‘pyriform’ stage, resulting in inhibiting the formation of a normal wide head lobe and an invagination occurring in its central region, the first sign of the mesoderm differentiation. This phenomenon proceeds gradually toward the posterior part and thus the differentiation of mesoderm becomes impossible throughout the entire length of germband. The results are discussed in the context of the mesoderm differentiation in Bombyx.

Keywords:

• Bombyx mori
• embryogenesis
• embryonic lethal mutant
• mesoderm