Jeffery W R, Ewing N, Machula J, Olsen C L, Swalla B J
Department of Biology, Pennsylvania State University, University Park 16802, USA.
Int J Dev Biol. 1998 Nov;42(8):1085-92.
We have examined the expression and regulation of cytoskeletal actin genes in ascidians with tailed (Molgula oculata) and tailless larvae (Molgula occulta). Four cDNA clones were isolated representing two pairs of orthologous cytoskeletal actin genes (CA1 and CA2), which encode proteins differing by five amino acids in the tailed and tailless species. The CA1 and CA2 genes are present in one or two copies, although several related genes may also be present in both species. Maternal CA1 and CA2 mRNA is present in small oocytes but transcript levels later decline, suggesting a role in early oogenesis. In the tailed species, embryonic CA1 and CA2 mRNAs first appear in the presumptive mesenchyme and muscle cells during gastrulation, subsequently accumulate in the presumptive notochord cells, and can be detected in these tissues through the tadpole stage. CA1 mRNAs accumulate initially in the same tissues in the tailless species but subsequently disappear, in concert with the arrest of notochord and tail development. In contrast, CA2 mRNAs were not detected in embryos of the tailless species. Fertilization of eggs of the tailless species with sperm of the tailed species, which restores the notochord and the tail, also results in the upregulation of CA1 and CA2 gene expression in hybrid embryos. Antisense oligodeoxynucleotide experiments suggest that CA1 and CA2 expression in the notochord, but not in the muscle cells, is dependent on prior expression of Mocc FHI, an ascidian HNF-3beta-like gene. The expression of the CA1 and CA2 genes in the notochord in the tailed species, downregulation in the tailless species, upregulation in interspecific hybrids, and dependence on HNF-3beta activity is consistent with a role of these genes in development of the ascidian notochord.
我们研究了有尾海鞘（眼状海鞘）和无尾幼虫（隐匿海鞘）中细胞骨架肌动蛋白基因的表达和调控。分离出了四个cDNA克隆，它们代表两对直系同源的细胞骨架肌动蛋白基因（CA1和CA2），在有尾和无尾物种中，这两个基因编码的蛋白质相差五个氨基酸。CA1和CA2基因以单拷贝或双拷贝形式存在，尽管这两个物种中可能也存在几个相关基因。母本的CA1和CA2 mRNA存在于小卵母细胞中，但转录水平随后下降，这表明其在早期卵子发生中起作用。在有尾物种中，胚胎期的CA1和CA2 mRNA最初在原肠胚形成期间出现在预定的间充质细胞和肌肉细胞中，随后在预定的脊索细胞中积累，并在蝌蚪阶段的这些组织中都能检测到。CA1 mRNA最初在无尾物种的相同组织中积累，但随后消失，这与脊索和尾巴发育的停滞相一致。相反，在无尾物种的胚胎中未检测到CA2 mRNA。用有尾物种的精子使无尾物种的卵子受精，恢复了脊索和尾巴，这也导致杂种胚胎中CA1和CA2基因表达上调。反义寡脱氧核苷酸实验表明，CA1和CA2在脊索中的表达，而不是在肌肉细胞中的表达，依赖于海鞘HNF-3β样基因Mocc FHI的先前表达。CA1和CA2基因在有尾物种的脊索中的表达、在无尾物种中的下调、在种间杂种中的上调以及对HNF-3β活性的依赖性，与这些基因在海鞘脊索发育中的作用一致。
