Drevet J R, Swevers L, Iatrou K
Department of Medical Biochemistry, Faculty of Medicine, University of Calgary, AB, Canada.
J Mol Biol. 1995 Feb 10;246(1):43-53. doi: 10.1006/jmbi.1994.0064.
Gene BmGATA beta of the silkworm Bombyx mori was previously shown to encode factor BCFI, which regulates the expression of a class of chorion genes expressed during the late stages of choriogenesis. We now show that the expression of the BmGATA beta gene is spatially and temporally regulated by alternative splicing that generates two major (BmGATA beta 1 and BmGATA beta 2) and one minor (BmGATA beta 3) mRNA isoforms of non-identical tissue distribution. The three isoforms differ in the organization of the DNA-binding domains of the corresponding polypeptides. While all three isoforms are expressed in ovarian follicular cells and in testes, only one of them, BmGATA beta 1, is gonad-specific. BmGATA beta 2 is expressed in a variety of other larval and pupal tissues, while BmGATA beta 3 is detected in some pupal but none of the larval tissues. Analysis of RNA isolated from follicular cells of developing ovarian follicles has shown that the onset of ovarian transcription for all three mRNA isoforms occurs during late vitellogenesis, and that the level of accumulated mRNA declines significantly at the onset of choriogenesis. Coincident with the onset of late chorion gene expression, we have observed a significant change in the preference of splice site selection in favour of the one that results in the generation of BmGATA beta 1 mRNA. The transcriptional activation of the BmGATA beta gene in follicular cells during late vitellogenesis correlates with the previously demonstrated initial accumulation of factor BCFI in the cytoplasm of follicular cells and its appearance in follicular cell nuclei only during the late stages of choriogenesis. The relationship between factor BCFI and the different polypeptides encoded by the three BmGATA beta mRNA isoforms is discussed.
家蚕基因BmGATAβ先前已被证明可编码因子BCFI，该因子调控一类在胚盘形成后期表达的绒毛膜基因的表达。我们现在表明，BmGATAβ基因的表达通过可变剪接在空间和时间上受到调控，可变剪接产生两种主要的（BmGATAβ1和BmGATAβ2）和一种次要的（BmGATAβ3）mRNA异构体，它们具有不同的组织分布。这三种异构体在相应多肽的DNA结合结构域的组织方式上有所不同。虽然这三种异构体都在卵巢滤泡细胞和睾丸中表达，但其中只有一种，即BmGATAβ1，是性腺特异性的。BmGATAβ2在多种其他幼虫和蛹组织中表达，而BmGATAβ3在一些蛹组织中被检测到，但在幼虫组织中均未检测到。对从发育中的卵巢滤泡的滤泡细胞中分离的RNA的分析表明，所有三种mRNA异构体的卵巢转录起始于卵黄发生后期，并且在胚盘形成开始时积累的mRNA水平显著下降。与晚期绒毛膜基因表达的开始同时，我们观察到剪接位点选择偏好发生了显著变化，有利于产生BmGATAβ1 mRNA的那个位点。卵黄发生后期滤泡细胞中BmGATAβ基因的转录激活与先前证明的因子BCFI在滤泡细胞细胞质中的初始积累及其仅在胚盘形成后期出现在滤泡细胞核中相关。本文讨论了因子BCFI与三种BmGATAβ mRNA异构体编码的不同多肽之间的关系。
