Structure and expression of the gene encoding a Broad-Complex homolog in the silkworm, Bombyx mori.
The steroid hormone ecdysone (20-hydroxyexdysone) initiates metamorphosis and also larval ecdysis in many insects by activating a cascade of genes that includes primary response genes (early genes), most of which encode transcriptional regulators, and secondary response genes (late genes) regulated by the early genes. One of the early genes, Broad-Complex (BR-C), a key regulator of the ecdysone cascade, shares a common amino-terminal BTB domain which is fused by alternative splicing to one of four pairs of C(2)H(2) zinc finger domains (Z1, Z2, Z3, and Z4). cDNAs for BR-C (BmBR-C) were isolated from the silkworm Bombyx mori. These genes showed 90.3% and 98.2% amino acid identity with the Drosophila BR-C and Manduca BR-C in the N-terminal BTB domain; 96.0%, 90.7%, and 85.2% identity with the three zinc finger domains of the Drosophila Z1, Z2, and Z4 isoforms; and 96.3% and 98.1% identity with the two zinc finger domains of the Manduca Z2 and Z4 isoforms, respectively. Partial genomic sequencing (from the 3' region of the core sequence to the 3' region of the Z3 class zinc finger-coding sequence) of the BmBR-C gene showed that four exons coding the zinc finger domains are arranged the same as the BR-C gene in Drosophila. The amino acid sequence predicted from the genomic sequence corresponding to the BmBR-C Z3 class zinc finger domain is 100% identical to the Z3 isoforms of Drosophila and Manduca. We examined expression patterns of the BmBR-C isoforms during late larval to pupal development in the epidermis, fatbody and silk gland. During the metamorphic transformation, the epidermis and silk gland are completely histolyzed; however, the fat body survives into the adult phase. Expression patterns of BmBR-C during development differed extensively between the histolyzed group and the survival group. The BmBR-C expression patterns in silk glands also differed between the anterior and other areas (the middle and posterior silk glands).
Nishita
Yoshinori
Y
Laboratory of Gene Function and Regulation, Center for Advanced Science and Technology, Hokkaido University, North 10, West 8, Kita-ku, Sapporo 060-0810, Japan.
Takiya
Shigeharu
S
D000595:Amino Acid Sequence; D000818:Animals; D012831:Bombyx / Q000235:genetics* / Q000254:growth & development; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D017344:Genes, Insect / Q000235:genetics; D019476:Insect Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D020033:Protein Isoforms / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011987:Receptors, Steroid / Q000235:genetics; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000235:genetics*
D018076:DNA, Complementary; D019476:Insect Proteins; D020033:Protein Isoforms; D012333:RNA, Messenger; D011987:Receptors, Steroid; D014157:Transcription Factors; C467903:ecdysone receptor A, insect