Widespread RNA segregation in a spiralian embryo
Widespread RNA segregation in a spiralian embryo
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DOI：
10.1111/j.1525-142x.2007.00194.x
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发表时间：
2007-11-01
影响因子：
2.9
通讯作者：
Lambert, J. David
中科院分区：
文献类型：
--
作者：
Kingsley, Evan P.;Chan, Xin Yi;Lambert, J. David
在多细胞生物体中，细胞不对称分裂是决定细胞命运的重要模式，但它们对早期胚胎模式的相对贡献在不同的类群中有所不同。在软体动物Ilyanassa的胚胎中，大多数早期细胞分裂是明显不对称的。在Ilyanassa早期卵裂过程中，几个保守的发育模式基因的mRNAs定位于间期中心体，然后在分裂期间，它们移动到皮质的一部分，该部分将由一个子细胞遗传。在这里，我们报告了一项关于Ilyanassa胚胎中RNA定位的公正调查，并研究了早期发育过程中中心体定位的总体模式。我们发现，在发育早期，3-4%的RNA特异性地定位于中心体，其余的要么普遍分布在细胞质中，要么与细胞质中的水平相比，在中心体上的含量较低。我们观察到从受精卵到第五个卵裂周期的所有细胞中RNA的中心体定位，以及在四细胞阶段之后的所有分裂中RNA的不对称分离。值得注意的是，每个特定定位的信息都是在早期分裂的一组独特的细胞中的中心体上发现的，而且大多数都是在24-细胞期的独特的细胞组中发现的。一些特定定位的RNA与其他胚胎中的发育调节蛋白同源。这些结果表明，在这个系统中，定位和分离的机制非常复杂，并表明这些事件参与了早期Ilyanassa胚胎所有谱系的细胞命运指定。我们认为，在早期卵裂中更多地依赖于决定因素的分离，增加了对软体动物和其他螺旋类群中卵裂模式的限制。
Asymmetric cell divisions are a crucial mode of cell fate specification in multicellular organisms, but their relative contribution to early embryonic patterning varies among taxa. In the embryo of the mollusc Ilyanassa, most of the early cell divisions are overtly asymmetric. During Ilyanassa early cleavage, mRNAs for several conserved developmental patterning genes localize to interphase centrosomes, and then during division they move to a portion of the cortex that will be inherited by one daughter cell. Here we report an unbiased survey of RNA localization in the Ilyanassa embryo, and examine the overall patterns of centrosomal localization during early development. We find that 3-4% of RNAs are specifically localized to centrosomes during early development, and the remainder are either ubiquitously distributed throughout the cytoplasm or weakly enriched on centrosomes compared with levels in the cytoplasm. We observe centrosomal localization of RNAs in all cells from zygote through the fifth cleavage cycle, and asymmetric RNA segregation in all divisions after the four-cell stage. Remarkably, each specifically localized message is found on centrosomes in a unique subset of cells during early cleavages, and most are found in unique sets of cells at the 24-cell stage. Several specifically localized RNAs are homologous to developmental regulatory proteins in other embryos. These results demonstrate that the mechanisms of localization and segregation are extraordinarily intricate in this system, and suggest that these events are involved in cell fate specification across all lineages in the early Ilyanassa embryo. We propose that greater reliance on segregation of determinants in early cleavage increases constraint on cleavage patterns in molluscs and other spiralian groups.