Patterns of region-specific chorion gene expression in the silkmoth and identification of shared 5' flanking genomic elements

The chorion genes of the medfly, Ceratitis capitata, I: Structural and regulatory conservation of the s36 gene relative to two Drosophila species

We have used low stringency screening with the Drosophila melanogaster s36 chorion gene to recover its homologue from genomic and cDNA libraries of the medfly, Ceratitis capitata. The same gene has also been recovered from a genomic library of D. virilis. The medfly s36 gene shows similar developmental specificity as in Drosophila (early choriogenesis). It is also specifically amplified in ovarian follicles; this is the first report of chorion gene amplification outside the genus Drosophila. Alignments of s36 sequences from three species show that, in addition to its regulatory conservation, the s36 gene is extensively conserved in sequence, in a region corresponding to a central protein domain, and in short regions of 5' flanking DNA that might correspond to cis-regulatory elements.

Transgenic regulation of moth chorion gene promoters in Drosophila: tissue, temporal, and quantitative control of four bidirectional promoters

Bidirectional chorion gene promoter regions from three silkmoth species, Bombyx mori, Antheraea pernyi, or Antheraea polyphemus (members of two different moth families), were tested for their ability to transcriptionally activate a bacterial marker gene (chloramphenicol acetyltransferase) in transformant Drosophila. Relatively short 5' flanking DNA fragments (272-367 bp) of chorion gene pairs are sufficient to confer a high degree of tissue and choriogenic stage specificity of expression to the marker gene. Thus, significant conservation of molecular interactions controlling transcription during choriogenesis is observed between the distantly related orders, Lepidoptera and Diptera. However, quantitative and fine temporal regulation in the Drosophila host does not fully parallel the in situ regulation in moths, indicating that some regulatory protein-DNA interactions have diversified in the approximately 250 million years since the last common ancestor of these insect groups. Limited in vitro mutagenesis of a B. mori promoter DNA has shown that a central 189-bp region includes elements sufficient for the qualitative specificity of chorion-specific expression. The same experiments have shown that a previously identified essential element, centered on the TCACGT hexamer, is not sufficient for chorion-specific expression: an additional essential element or elements are found farther upstream, within a 112-bp DNA region. Comparisons of silkmoth and Drosophila chorion gene promoter sequences have identified some candidates for cis-acting elements involved in the developmental regulation of chorion gene expression.

Evolution of chorion structural genes and regulatory mechanisms in two wild silkmoths: a preliminary analysis

We report a preliminary analysis of structural and regulatory evolution of the A and B chorion gene families in two wild silkmoths, Antheraea pernyi and Antheraea polyphemus. Homospecific and heterospecific dot hybridizations were performed between previously characterized A. polyphemus complementary DNA clones and total or stage-specific follicular mRNAs from the two species. The hybridization patterns indicated substantial interspecies changes in the abundance of corresponding mRNA sequences (heteroposic evolution) without substantial changes in their developmental specificities (heterochronic evolution). In addition, the proteins encoded in the two species by corresponding mRNAs were determined by hybrid-selected translation followed by electrophoretic analysis. The results suggested that the proteins evolve in size, presumably through internal deletions and duplications.

Organization and expression of three genes from the silkmoth early chorion locus

Chorion genes in the silkmoth Bombyx mori are clustered in a small region of one chromosome. Genes are grouped within this locus according to their expression in either early, middle, or late stages of choriogenesis. The entire set of late genes and a large fraction of the middle genes have been cloned and extensively characterized. We report here the first molecular characterization of a set of early chorion genes clustered within a 22.5-kb region. Transcripts homologous to these genes appear in the very first choriogenic follicle but disappear with different kinetics. One of the three early genes, 5H4, is the first example of a chorion gene which is not a member of a multigene family, or divergently paired with another chorion gene. The other two early genes, (ErA.1 and ErB.1) are divergently paired with each other in the manner of the middle and late chorion genes. The common 5' region between ErA.1 and ErB.1 is significantly shorter and does not contain certain sequence elements shared by the highly conserved 5' regions of middle and late chorion gene pairs. This evidence taken together with the fact that 5H4 is unpaired indicates that the early genes may utilize a regulatory mechanism somewhat different from the middle and late gene families.