Van Kempen M J, Vermeulen J L, Moorman A F, Gros D, Paul D L, Lamers W H
Department of Anatomy and Embryology, University of Amsterdam, Netherlands.
Cardiovasc Res. 1996 Nov;32(5):886-900. doi: 10.1016/0008-6363(96)00131-9.
Gap junctions have been demonstrated ultrastructurally in cardiac regions where connexin40 (Cx40) and connexin43 (Cx43) protein could not be detected immunohistochemically. We investigated therefore the distribution of their mRNAs with more sensitive techniques.
In situ hybridizations with Cx40 and Cx43 cRNA probes were performed on sections of rat hearts from 9 embryonic days (ED 9) to adults.
From ED 13, Cx40 and Cx43 mRNA are detectable in atria and ventricles, but not in their flanking myocardium (inflow tract, atrioventricular canal and outflow tract). Even though Cx40 and Cx43 mRNA eventually become expressed in the inflow tract, they remain undetectable in the sinoatrial node, the atrioventricular canal (including atrioventricular node) and outflow tract. Expression of Cx40 is maximal in the fetal period and declines towards birth. Cx40 expression in the left and right ventricles evolves independently, its mRNA disappearing 4 days earlier from the right than from the left ventricle, and earlier from the free wall than from the trabeculations. Expression of Cx43 mRNA increases during development and changes postnatally from uniform to punctate. Prenatally, Cx43 mRNA was strongest in the subepicardial layer of the ventricular free wall. Nevertheless, we did not detect protein in this layer.
Cardiac regions without detectable Cx40 or Cx43 mRNA either have extremely low levels of expression or express a different connexin. The temporally separate disappearance of Cx40 mRNA from the fetal ventricles implies that left and right ventricles mature independently with respect to gap-junctional communication. The division of the developing heart in compartments where Cx40 and Cx43 mRNA can and cannot be detected, implies pretranslationally regulated gene expression. The postnatally observed subcellular redistribution of Cx43 mRNA coincides with a reported increase in protein expression.
超微结构研究已证实心脏某些区域存在缝隙连接，但免疫组织化学方法未能检测到连接蛋白40（Cx40）和连接蛋白43（Cx43）。因此，我们采用更灵敏的技术研究了它们mRNA的分布情况。
用Cx40和Cx43 cRNA探针，对从胚胎第9天（ED 9）到成年大鼠心脏切片进行原位杂交。
从胚胎第13天起，心房和心室可检测到Cx40和Cx43 mRNA，但在其相邻心肌（流入道、房室管和流出道）中未检测到。尽管Cx40和Cx43 mRNA最终在流入道表达，但在窦房结、房室管（包括房室结）和流出道中仍未检测到。Cx40在胎儿期表达最高，出生时下降。左、右心室中Cx40的表达独立变化，其mRNA从右心室消失的时间比左心室早4天，从游离壁消失比从肌小梁早。Cx43 mRNA的表达在发育过程中增加，出生后从均匀分布变为点状分布。产前，Cx43 mRNA在心室游离壁的心外膜下层表达最强。然而，我们在该层未检测到蛋白质。
未检测到Cx40或Cx43 mRNA的心脏区域，要么表达水平极低，要么表达其他连接蛋白。Cx40 mRNA在胎儿心室中先后消失，这意味着左、右心室在缝隙连接通讯方面独立成熟。发育中的心脏可分为能检测到和不能检测到Cx40与Cx43 mRNA的区域，这意味着基因表达存在翻译前调控。出生后观察到的Cx43 mRNA亚细胞重分布，与报道的蛋白质表达增加一致。
