Differential patterns in the temporal experession ofBombyx mori chorion genes.

cDNA clones for two distinct families ofBombyx mori chorion protiens, Class A (m2774) and Class Hc (m5000), were used to study the developmental regulation of specific chorion mRNAs. Individual follicles from maturing ovarioles were assayed by Northern blotting techniques and amino acid pulse-labeling to determine concomitant RNA accumulation and protein synthesis patterns with a temporal resolution of 2.2-2.6 h of developmental age. RNAs hybridizing to the two cloned chorion sequences at high criterion showed distinctive, non-overlapping patterns of accumulation during the middle-late and very late stages of choriogenesis. Moreover, the periods of expression of these RNAs coincided exactly with the synthetic periods of two distinct subsets of chorion proteins, one containing Class A and B components, and the other containing Class Hc components alone. These results suggest that chorion gene transcription and translation are tightly coupled.