Inhibition of the binding of MSG-intermolt-specific complex, MIC, to the sericin-1 gene promoter and sericin-1 gene expression by POU-M1/SGF-3.
The sericin-1 gene encoding a glue protein is expressed in the middle silk gland (MSG) of the silkworm, Bombyx mori. A member of the class III POU domain transcription factors, POU-M1, was cloned as the factor bound to the SC site of the sericin-1 promoter and has been proposed to be a positive transcription factor. In this study, we analyzed the expression pattern of the POU-M1 gene in fourth and fifth instars in comparison with the pattern of the sericin-1 gene. The POU-M1 gene was expressed strongly in the region anterior to the sericin-1-expressing portion of the silk gland at both feeding stages. As the sericin-1-expressing region expands from the posterior to middle portions of the MSG in the fifth instar, the POU-M1-expressing region retreated from the middle to anterior portion. Introduction of the expression vector of POU-M1 into the silk glands by gene gun technology repressed promoter activity of the sericin-1 gene, suggesting that POU-M1 regulates the sericin-1 gene negatively. An in vitro binding assay showed that POU-M1 bound not only to the SC site but also to other promoter elements newly detected in vivo. Another spatiotemporal specific factor MIC binds to these elements, and POU-M1 competed with MIC to bind at the -70 site essential for promoter activity. These results suggest that POU-M1 is involved in restricting the anterior boundary of the sericin-1-expressing region in the silk gland by inhibiting the binding of the transcriptional activator to the promoter elements.
Graduate School of Life Science, Hokkaido University, Kita-ku, Sapporo, Japan.
Mai
M
Kimoto
Tsuyuki
T
Kitagawa
Isao
I
Kobayashi
Tomohiro
T
Nakata
Asato
A
Kuroiwa
Shigeharu
S
Takiya
D000818:Animals; D001483:Base Sequence; D012831:Bombyx / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D005786:Gene Expression Regulation; D019476:Insect Proteins / Q000235:genetics* / Q000378:metabolism; D007814:Larva / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D050809:POU Domain Factors / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D016415:Sequence Alignment; D047030:Sericins / Q000235:genetics*; D015533:Transcriptional Activation
D019476:Insect Proteins; D050809:POU Domain Factors; C085604:POU-M1 protein, Bombyx mori; D047030:Sericins