Beach R L, Jeffery W R
Department of Zoology, University of Texas, Austin.
Dev Genet. 1990;11(1):2-14. doi: 10.1002/dvg.1020110103.
We have cloned and characterized the temporal and spatial expression of ScCA15, a cDNA clone encoding an actin gene in the ascidian Styela clava. The partial nucleotide and derived amino acid sequences of this singlecopy gene suggest that it is a cytoskeletal actin. Northern analysis shows that ScCA15 corresponds to a 1.8-kb mRNA that is transcribed during oogenesis, during embryonic development, and in the adult. In situ hybridization shows that maternal ScCA15 mRNA is distributed uniformly in the cytoplasm of the oocyte and unfertilized egg. During the period of ooplasmic segregation following fertilization, however, ScCA15 mRNA appears to be translocated into the ectoplasm, a specialized cytoplasmic region of the egg. During the early cleavages, the ectoplasmic transcripts are partitioned to ectodermal cells in the animal hemisphere, which are precursors of the epidermis and nervous system of the larva. Maternal ScCA15 mRNA is degraded just before gastrulation and replaced by zygotic transcripts which begin to accumulate between the neurula and mid-tailbud stages. Zygotic ScCA15 mRNA accumulates primarily in the epidermal and neural cells, although lower levels of these transcripts may also be present in tail muscle cells. These results show that two mechanisms are used to concentrate ScCA15 mRNA in the ectodermal cells during development: 1) localization and differential segregation of maternal transcripts and 2) specific expression of the ScCA15 gene. ScCA15 mRNA is detected by in situ hybridization in the testes, ovaries, alimentary tract, and endostyle of adults. In the testes, ScCA15 mRNA is present in developing sperm, whereas in the ovary, these transcripts are present in the germinal epithelium and developing oocytes. In the alimentary tract, ScCA15 mRNA is confined to the gastric epithelium of the esophagus, stomach, and intestine. Since the ScCA15 gene is expressed in embryonic and adult tissues that are undergoing rapid cell division, this actin is likely to function in some aspect of cell proliferation.
我们已经克隆并鉴定了ScCA15的时空表达，ScCA15是编码海鞘柄海鞘肌动蛋白基因的一个cDNA克隆。这个单拷贝基因的部分核苷酸和推导的氨基酸序列表明它是一种细胞骨架肌动蛋白。Northern分析显示ScCA15对应于一个1.8kb的mRNA，该mRNA在卵子发生、胚胎发育和成年期均有转录。原位杂交显示，母本ScCA15 mRNA均匀分布在卵母细胞和未受精卵的细胞质中。然而，在受精后的卵质分离期，ScCA15 mRNA似乎被转运到外质中，外质是卵子的一个特殊细胞质区域。在早期卵裂过程中，外质转录本被分配到动物半球的外胚层细胞中，这些细胞是幼虫表皮和神经系统的前体。母本ScCA15 mRNA在原肠胚形成前被降解，并被合子转录本取代，合子转录本在神经胚和中尾芽期之间开始积累。合子ScCA15 mRNA主要在表皮和神经细胞中积累，尽管在尾肌细胞中也可能存在较低水平的这些转录本。这些结果表明，在发育过程中有两种机制用于将ScCA15 mRNA集中在外胚层细胞中：1）母本转录本的定位和差异分离；2）ScCA15基因的特异性表达。通过原位杂交在成年个体的睾丸、卵巢、消化道和内柱中检测到ScCA15 mRNA。在睾丸中，ScCA15 mRNA存在于发育中的精子中，而在卵巢中，这些转录本存在于生发上皮和发育中的卵母细胞中。在消化道中，ScCA15 mRNA局限于食管、胃和肠的胃上皮。由于ScCA15基因在正在进行快速细胞分裂的胚胎和成年组织中表达，这种肌动蛋白可能在细胞增殖的某些方面发挥作用。
