Brunekreef G A, van Genesen S T, Destrée O H, Lubsen N H
Department of Molecular Biology, University of Nijmegen, The Netherlands.
Invest Ophthalmol Vis Sci. 1997 Dec;38(13):2764-71.
Extralenticular expression of alpha- and beta-crystallin genes has been demonstrated in mammals and expression of gamma-crystallin genes has been shown in Xenopus laevis. To determine a possible correlation between lens determination and crystallin gene expression, the site of expression of (a member of) the alpha-, beta-, and gamma-crystallin gene families was observed before and during lens formation in X. laevis.
The partial complementary DNAs (cDNAs) of alpha A- and beta A4-crystallin and a gamma-crystallin were cloned from an X. laevis lens cDNA library. The corresponding antisense RNAs were used to analyze the expression of these genes during X. laevis development by wholemount in situ hybridization.
Expression of the beta A4- and gamma-crystallin (but not alpha-crystallin) genes could first be detected in the animal cap of the X. laevis gastrula. The beta A4- and gamma-crystallin messengers were also found in the first stage of lens development, when the ectodermal tissue overlying the optic vesicle thickens to form the lens placode. alpha A-crystallin messenger RNAs were only detectable when the lens epithelial cells were formed.
In contrast to observations in most vertebrates, expression of the beta A4- and gamma-crystallin genes was observed to precede that of the alpha A-crystallin gene during lens development of X. laevis, reflecting the determination that in amphibians, the (presumptive) fiber cells are formed before the epithelial cells, whereas in vertebrates, the order is reversed. Expression of beta A4- and gamma-crystallin genes in the ectodermal tissue of the X. laevis gastrula shows that these genes are expressed when this tissue gains competence for lens formation.
已证实在哺乳动物中α-和β-晶状体蛋白基因存在晶状体外表达，且在非洲爪蟾中已显示γ-晶状体蛋白基因有表达。为了确定晶状体决定与晶状体蛋白基因表达之间可能存在的关联，在非洲爪蟾晶状体形成之前及形成过程中观察了α-、β-和γ-晶状体蛋白基因家族（其中一个成员）的表达位点。
从非洲爪蟾晶状体cDNA文库中克隆出αA-和βA4-晶状体蛋白以及一种γ-晶状体蛋白的部分互补DNA（cDNA）。通过整装原位杂交，使用相应的反义RNA来分析这些基因在非洲爪蟾发育过程中的表达。
βA4-和γ-晶状体蛋白（而非α-晶状体蛋白）基因的表达最初可在非洲爪蟾原肠胚的动物帽中检测到。在晶状体发育的第一阶段，当覆盖视泡的外胚层组织增厚形成晶状体板时，也发现了βA4-和γ-晶状体蛋白信使核糖核酸。仅在晶状体上皮细胞形成时才能检测到αA-晶状体蛋白信使核糖核酸。
与大多数脊椎动物的观察结果相反，在非洲爪蟾晶状体发育过程中，观察到βA4-和γ-晶状体蛋白基因的表达先于αA-晶状体蛋白基因，这反映出在两栖动物中，（推测的）纤维细胞在上皮细胞之前形成，而在脊椎动物中顺序相反。βA4-和γ-晶状体蛋白基因在非洲爪蟾原肠胚外胚层组织中的表达表明，当该组织获得形成晶状体的能力时这些基因就会表达。
