Studies on embryonic diapause in thepnd mutant of the silkworm,Bombyx mori : V. Identification of apnd + gene-specific protein.

Two-dimensional gel electrophoresis has been used to analyse patterns of proteins synthesized in the eggs from theBombyx mutantpnd, whose homozygous embryo never enters diapause owing to a genetic defect. At the middle to late stage of gastrulation the diapause type of the heterozygous embryo, derived from a homozygouspnd female mated to a wild-type male, synthesizes eight proteins which are not detected in the homozygouspnd embryo. To examine the relationship between embryonic diapause and the appearance of the heterozygote-specific proteins, the pattern of proteins synthesized in the heterozygotes of the diapause type was compared with that in heterozygotes which were artificially altered so that they would continue development. Only one of the eight heterozygote-specific proteins was constitutively synthesized according to the embryonic genome, irrespective of their developmental state, whereas appearance of the remaining seven proteins was exclusively dependent on their developmental nature. This finding strongly suggests that the unique protein might result from the expression of thepnd + gene, and the other proteins might be synthesized along with diapause initiation in the heterozygotes. The possible role of the putativepnd + gene-specific protein at the onset of embryonic diapause is discussed in relation to the action of the diapause factor, which predetermines embryonic diapause by affecting the developing oocytes.