A complex set of early chorion DNA sequences from Bombyx mori

A follicular cDNA library from Bombyx mori (576 clones) was screened to obtain a representative sample of chorion sequences differentially expressed during the early period of choriogenesis. Ten selected sequences were characterized by Northern analysis and by dot blots of stage-specific RNA. Five of these sequences (represented in the library by 24 clones) had the developmental specificity and transcript size expected of early chorion components; two sequences (37 clones) had the developmental specificity expected of middle and late chorion components; and three sequences (16 clones) were presumed to be non-chorion, since they are constitutive or disappear at the beginning of choriogenesis. The five recovered early chorion cDNA components have been sequenced, and define three distinct subfamilies of the chorion B multigene family, and two C type families. The complexity of the early chorion genes in B. mori is discussed.