Cell-specific expression in the silkmoth follicle: developmental characterization of a major chorion protein, its mRNA and gene.

Choriogenesis (eggshell formation) within the silkmoth Antheraea polyphemus proceeds in parallel for the two major subpopulations of follicle cells, diverging only during the very late period when aeropyle crown surface structures form in one region but not in the other. Correlated with their appearance is the synthesis of a set of region-specific proteins. In this report, aeropyle crowns are physically isolated and their protein composition is shown to consist of those same region-specific proteins. A cDNA clone, called pcvl 16, has been selected and shown to encode a lamellar-forming, aeropyle crown-specific protein, probably of the previously described C3,4 group. These conclusions are based on hybrid-selected translation, Northern analysis, and sequence analysis. pcvl 16 was used to isolate two distinct cloned copies of the 16 gene. Both 16 genes are closely paired with another region-specific gene but the proximity of the two gene pairs to each other is uncertain. Non-region-specific chorion genes expressed at earlier times in choriogenesis surround the 16 gene pairs, suggesting that cis sequences necessary for regionalized expression may be closely linked to coding sequences. To test this hypothesis, 5'-flanking sequences from eight region-specific genes are compared and shown to share two oligonucleotide sequences. One is a known regulatory element found in virtually all moth and fly chorion genes examined. The other, located just upstream from the TATA box, is not found in non-regionally expressed chorion genes and, thus, is a candidate for specifying regional expression.