Bouget F. Y., Gerttula S., Shaw S. L., Quatrano R. S.
Department of Biology, University of North Carolina, Chapel Hill, North Carolina 27599-3280.
Plant Cell. 1996 Feb;8(2):189-201. doi: 10.1105/tpc.8.2.189.
Localization of mRNA is a well-described mechanism to account for the asymmetric distribution of proteins in polarized somatic cells and embryos of animals. In zygotes of the brown alga Fucus, F-actin is localized at the site of polar growth and accumulates at the cell plates of the first two divisions of the embryo. We used a nonradioactive, whole-mount in situ hybridization protocol to show the pattern of actin mRNA localization. Until the first cell division, the pattern of actin mRNA localization is identical to that of total poly(A)+ RNA, that is, a symmetrical distribution in the zygote followed by an actin-dependent accumulation at the thallus pole at the time of polar axis fixation. At the end of the first division, actin mRNA specifically is redistributed from the thallus pole to the cell plates of the first two divisions in the rhizoid. This specific pattern of localization in the zygote and embryo involves the redistribution of previously synthesized actin mRNA. The initial asymmetry of actin mRNA at the thallus pole of the zygote requires polar axis fixation and microfilaments but not microtubules, cell division, or polar growth. However, redistribution of actin mRNA from the thallus pole to the first cell plate is insensitive to cytoskeletal inhibitors but is dependent on cell plate formation. The F-actin that accumulates at the rhizoid tip is not accompanied by the localization of actin mRNA. However, maintenance of an accumulation of actin protein at the cell plates of the rhizoid could be explained, at least partially, by a mechanism involving localization of actin mRNA at these sites. The pattern and requirements for actin mRNA localization in the Fucus embryo may be relevant to polarization of the embryo and asymmetric cell divisions in higher plants as well as in other tip-growing plant cells.
mRNA 定位是一种已被充分描述的机制，用于解释极化体细胞和动物胚胎中蛋白质的不对称分布。在褐藻墨角藻的合子中，F-肌动蛋白定位于极性生长部位，并在胚胎的前两次分裂的细胞板处积累。我们使用非放射性的全组织原位杂交方案来显示肌动蛋白 mRNA 的定位模式。在第一次细胞分裂之前，肌动蛋白 mRNA 的定位模式与总 poly(A)+ RNA 的定位模式相同，即在合子中呈对称分布，随后在极轴固定时在叶状体极处依赖肌动蛋白进行积累。在第一次分裂结束时，肌动蛋白 mRNA 特异性地从叶状体极重新分布到假根中前两次分裂的细胞板处。合子和胚胎中这种特定的定位模式涉及先前合成的肌动蛋白 mRNA 的重新分布。合子叶状体极处肌动蛋白 mRNA 的初始不对称性需要极轴固定和微丝，但不需要微管、细胞分裂或极性生长。然而，肌动蛋白 mRNA 从叶状体极到第一个细胞板的重新分布对细胞骨架抑制剂不敏感，但依赖于细胞板的形成。在假根尖端积累的 F-肌动蛋白并没有伴随着肌动蛋白 mRNA 的定位。然而，假根细胞板处肌动蛋白蛋白积累的维持至少可以部分地通过一种涉及肌动蛋白 mRNA 在这些部位定位的机制来解释。墨角藻胚胎中肌动蛋白 mRNA 定位的模式和要求可能与高等植物以及其他顶端生长的植物细胞中胚胎的极化和不对称细胞分裂有关。
