Marsden M, Burke R D
Department of Biology, University of Victoria, British Columbia, Canada.
Dev Biol. 1997 Jan 15;181(2):234-45. doi: 10.1006/dbio.1996.8451.
Cell surface molecules that mediate adhesion in sea urchin embryos have been implicated in morphogenesis, and yet the molecules remain largely uncharacterized. Here we report evidence from PCR amplification for three novel beta integrin subunits that are expressed during early development of Strongylocentrotus purpuratus. The full cDNA sequence for one of these, betaG, bears a 59% similarity to Drosophila betaPS and a 58% similarity to vertebrate integrins. betaG closely resembles the beta1 subunit of vertebrates, particularly in the cytoplasmic domain where amino acids of the human beta1 subunit implicated in cell adhesion and signaling are conserved. The betaG subunit is detectable as a maternal, 7.5-kb transcript in eggs and expression peaks during gastrulation. Immunoblots with antiserum raised against a bacterially expressed fragment of the betaG subunit have bands with apparent molecular weights of about 130 kDa under reducing conditions and 110 kDa under nonreducing conditions. Immunoprecipitations suggest that betaG associates with at least two alpha subunits in gastrula stage embryos. In situ RNA hybridization of the betaG subunit indicates that all cells of the embryo express this molecule prior to gastrulation. In gastrulae, hybridization of the probe is highest in primary mesenchyme, secondary mesenchyme, the developing gut, and pigment cells. In immunolocalizations all cells of the blastulae express the protein at low levels and primary mesenchyme cells express betaG after they enter the blastocoel. Expression of the protein appears to be downregulated in the archenteron throughout gastrulation. betaG protein expression is also evident on secondary mesenchyme as they ingress and migrate in the blastocoel. We conclude that sea urchin embryos express integrins that are structurally similar to those characterized in other animals. Because betaG is expressed by migrating mesenchyme and yet is downregulated by rearranging epithelia, we suggest that this subunit has several functions during early development.
介导海胆胚胎黏附的细胞表面分子与形态发生有关，然而这些分子在很大程度上仍未得到充分表征。在此，我们报告了来自PCR扩增的证据，证明在紫海胆早期发育过程中表达了三种新型β整合素亚基。其中之一βG的完整cDNA序列与果蝇βPS有59%的相似性，与脊椎动物整合素有58%的相似性。βG与脊椎动物的β1亚基非常相似，特别是在细胞质结构域，其中人类β1亚基中与细胞黏附和信号传导有关的氨基酸是保守的。βG亚基在卵中可检测为母体7.5 kb转录本，在原肠胚形成期间表达达到峰值。用针对βG亚基细菌表达片段产生的抗血清进行免疫印迹，在还原条件下有表观分子量约为130 kDa的条带，在非还原条件下为110 kDa。免疫沉淀表明，βG在原肠胚阶段胚胎中与至少两个α亚基相关联。βG亚基的原位RNA杂交表明，在原肠胚形成之前胚胎的所有细胞都表达这种分子。在原肠胚中，探针杂交在初级间充质、次级间充质、发育中的肠道和色素细胞中最高。在免疫定位中，囊胚的所有细胞都低水平表达该蛋白，初级间充质细胞在进入囊胚腔后表达βG。在整个原肠胚形成过程中，该蛋白在原肠中的表达似乎下调。βG蛋白在次级间充质进入并在囊胚腔中迁移时也有明显表达。我们得出结论，海胆胚胎表达的整合素在结构上与其他动物中表征的整合素相似。由于βG由迁移的间充质表达，但在重排上皮细胞时下调，我们认为该亚基在早期发育过程中有多种功能。
