van der Zee Maurijn, Benton Matthew A, Vazquez-Faci Tania, Lamers Gerda E M, Jacobs Chris G C, Rabouille Catherine
Hubrecht Institute for Developmental Biology and Stem Cell Research, Uppsalalaan 8, Utrecht 3584 CT, The Netherlands Institute of Biology, Leiden University, Sylviusweg 72, Leiden 2333 BE, The Netherlands
Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK.
Development. 2015 Jun 15;142(12):2173-83. doi: 10.1242/dev.097113. Epub 2015 May 26.
In insects, the fertilized egg undergoes a series of rapid nuclear divisions before the syncytial blastoderm starts to cellularize. Cellularization has been extensively studied in Drosophila melanogaster, but its thick columnar blastoderm is unusual among insects. We therefore set out to describe cellularization in the beetle Tribolium castaneum, the embryos of which exhibit a thin blastoderm of cuboidal cells, like most insects. Using immunohistochemistry, live imaging and transmission electron microscopy, we describe several striking differences to cellularization in Drosophila, including the formation of junctions between the forming basal membrane and the yolk plasmalemma. To identify the nature of this novel junction, we used the parental RNAi technique for a small-scale screen of junction proteins. We find that maternal knockdown of Tribolium innexin7a (Tc-inx7a), an ortholog of the Drosophila gap junction gene Innexin 7, leads to failure of cellularization. In Inx7a-depleted eggs, the invaginated plasma membrane retracts when basal cell closure normally begins. Furthermore, transiently expressed tagged Inx7a localizes to the nascent basal membrane of the forming cells in wild-type eggs. We propose that Inx7a forms the newly identified junctions that stabilize the forming basal membrane and enable basal cell closure. We put forward Tribolium as a model for studying a more ancestral mode of cellularization in insects.
在昆虫中，受精卵在合胞体胚盘开始细胞化之前会经历一系列快速的核分裂。果蝇的细胞化过程已得到广泛研究，但其厚柱状胚盘在昆虫中并不常见。因此，我们着手描述赤拟谷盗的细胞化过程，其胚胎具有像大多数昆虫一样的由立方形细胞构成的薄胚盘。我们运用免疫组织化学、实时成像和透射电子显微镜技术，描述了与果蝇细胞化过程的几个显著差异，包括在形成的基膜和卵黄质膜之间形成连接。为了确定这种新型连接的性质，我们使用亲代RNA干扰技术对连接蛋白进行小规模筛选。我们发现，赤拟谷盗innexin7a（Tc-inx7a）的母体敲低，Tc-inx7a是果蝇间隙连接基因Innexin 7的直系同源基因，会导致细胞化失败。在Inx7a缺失的卵中，当基底细胞正常开始闭合时，内陷的质膜会缩回。此外，瞬时表达的带标签Inx7a定位于野生型卵中正在形成的细胞的新生基膜上。我们提出Inx7a形成了新发现的连接，这些连接稳定了正在形成的基膜并使基底细胞能够闭合。我们提出将赤拟谷盗作为研究昆虫更原始细胞化模式的模型。
