Tam L W, Stamer K A, Kirk D L
Department of Biology, Washington University, St. Louis, Missouri 63130.
Dev Biol. 1991 May;145(1):67-76. doi: 10.1016/0012-1606(91)90213-m.
In situ hybridization was used to resolve details of the temporal and spatial aspects of expression of a number of cell-type-specific genes of Volvox carteri. In confirmation of earlier results obtained by Northern-blot analysis, this study revealed that accumulation of transcripts of somatic genes was largely restricted to the somatic-cell lineage. In extension of the previous study, two distinct gene expression programs during somatic-cell development were more fully defined: "early" somatic genes were expressed in the somatic-cell lineage even before visible differentiation began, whereas "late" somatic genes were not expressed until after somatic cells had been visibly differentiated for more than a day and had already reached the presenescent-adult stage of development. We postulate that products of the early somatic genes may be involved in generalized somatic functions that are required throughout somatic-cell development, whereas the late somatic gene products may be involved in more specialized processes that characterize mature, parental somatic cells. The most significant finding of the present study is that transcripts of early somatic genes are significantly more abundant in presumptive somatic cells than in presumptive gonidia during embryonic stages, while the two cell types are linked by a network of cytoplasmic bridges. The fact that the two cell lineages can establish and maintain different transcript populations despite the extensive cytoplasmic continuity that exists between them is somewhat surprising and must be taken into account in future attempts to elucidate the way in which dichotomous differentiation is initiated in the organism.
原位杂交技术被用于解析团藻（Volvox carteri）多种细胞类型特异性基因表达在时间和空间方面的细节。为证实早期通过Northern印迹分析获得的结果，本研究表明体细胞基因转录本的积累在很大程度上局限于体细胞谱系。在前一项研究的基础上，本研究更全面地定义了体细胞发育过程中的两个不同基因表达程序：“早期”体细胞基因在可见分化开始之前就在体细胞谱系中表达，而“晚期”体细胞基因直到体细胞明显分化超过一天并已达到发育的衰老前-成体阶段才开始表达。我们推测，早期体细胞基因的产物可能参与整个体细胞发育过程中所需的一般体细胞功能，而晚期体细胞基因产物可能参与成熟亲本体细胞所特有的更特殊的过程。本研究最显著的发现是，在胚胎阶段，早期体细胞基因的转录本在假定的体细胞中比在假定的生殖细胞中丰富得多，而这两种细胞类型通过细胞质桥网络相连。尽管两种细胞谱系之间存在广泛的细胞质连续性，但它们能够建立并维持不同的转录本群体，这一事实有些令人惊讶，在未来试图阐明生物体中二分式分化启动方式的研究中必须予以考虑。
