Hanson-Painton O, Randolph V, Saugstad J A, Oh S K, Tobin S L
Department of Chemistry, University of Central Oklahoma, Edmond 73034.
Int J Dev Biol. 1992 Sep;36(3):343-51.
The highly conserved, intracellular calcium binding protein calmodulin is present in all cells at all times. In addition to this constitutive level, the amount of calmodulin is highly regulated according to the tissue or stage of development. Since there are only a few genes or a single gene for this protein in most species, intricate regulatory elements may be necessary to effect its complex regulation. This report adds new information concerning the gene structure and outlines the developmental and spatial regulation of Drosophila melanogaster calmodulin transcripts. The gene contains five exons, including a 49 bp exon in the 5' untranslated region, and spans over 16 kb. Homologues to this small, 5' noncoding exon have not been found in other calmodulin genes. The combined level of the transcripts is developmentally regulated, and the relative amounts of the two transcript size classes (1.65 kb and 1.9 kb) are differentially regulated during development. Primer extension experiments and RNase protection mapping show that both size classes of Drosophila calmodulin transcripts initiate at the same site but undergo alternative termination within the final exon. The spatial distribution of calmodulin transcripts was examined by in situ hybridization to sections of adults and to developmentally staged whole mount embryos. Calmodulin transcripts are evenly distributed early in embryogenesis. In later stages of embryogenesis, higher levels accumulate in the developing nerve cord and other tissues. Elevated levels of calmodulin transcripts are seen quite distinctly in the adult neural tissues and in the photoreceptor region of the compound eye.
高度保守的细胞内钙结合蛋白钙调蛋白始终存在于所有细胞中。除了这种组成性水平外，钙调蛋白的量还根据组织或发育阶段受到高度调节。由于大多数物种中该蛋白只有少数几个基因或单个基因，因此可能需要复杂的调控元件来实现其复杂的调节。本报告增加了有关该基因结构的新信息，并概述了黑腹果蝇钙调蛋白转录本的发育和空间调节。该基因包含五个外显子，包括5'非翻译区的一个49 bp外显子，跨度超过16 kb。在其他钙调蛋白基因中未发现与这个小的5'非编码外显子同源的序列。转录本的综合水平受到发育调控，并且在发育过程中，两种转录本大小类别（1.65 kb和1.9 kb）的相对量受到差异调节。引物延伸实验和核糖核酸酶保护图谱分析表明，果蝇钙调蛋白转录本的两种大小类别都在同一位点起始，但在最后一个外显子内经历选择性终止。通过对成虫切片和发育阶段的整装胚胎进行原位杂交，研究了钙调蛋白转录本的空间分布。钙调蛋白转录本在胚胎发育早期均匀分布。在胚胎发育后期，较高水平的转录本在发育中的神经索和其他组织中积累。在成年神经组织和复眼的光感受器区域可以非常明显地看到钙调蛋白转录本水平升高。
