Simonneau L, Broders F, Thiery J P
Laboratoire de Physiopathologie du Développement, CNRS URA 1337, Paris, France.
Dev Dyn. 1992 Aug;194(4):247-60. doi: 10.1002/aja.1001940402.
Cadherins are Ca(++)-dependent cell adhesion molecules which play a key role in morphogenesis and histogenesis. Two mRNAs clones (8 and 9) corresponding to two N-cadherin pseudo-allelic genes are present in Xenopus laevis. We report here that these transcripts share a highly homologous coding region but diverge in the non-coding region. We have determined the pattern of N-cadherin expression at the mRNA level by in situ hybridization with a riboprobe complementary to the EC5 domain of Xenopus N-cadherin clone 8. This part of the sequence is the least conserved in the cadherin gene family, minimizing the risk of cross-hybridization to other cadherins. N-cadherin transcripts are not detectable in the first stages of development. Expression first appears in the neural plate and reaches its maximum level in the CNS at tailbud stage. From early tadpole, it diminishes, so that a very weak signal is detected in the premetamorphic frog brain. N-cadherin expression is not uniform within the CNS, with some areas such as the roof of the rhombencephalon and the olfactory bulbs expressing higher levels of the transcripts. N-cadherin is present in several mesodermal derivatives such as the notochord, the pronephros, and the heart. It is, however, virtually absent from the myotomes and appears in skeletal muscles at later stages of differentiation. All placodes express high levels of N-cadherin. The non-neural ectoderm and the endoderm are always negative. In the brain and the heart, high levels of hybridization are observed with probes corresponding to both copies of the N-cadherin pseudo-allelic genes in their 5' non-coding region, indicating that both alleles are transcribed.
钙黏着蛋白是依赖钙离子的细胞黏附分子，在形态发生和组织发生中起关键作用。非洲爪蟾中存在两个与两个N-钙黏着蛋白假等位基因相对应的mRNA克隆（8和9）。我们在此报告，这些转录本共享高度同源的编码区，但在非编码区存在差异。我们通过与与非洲爪蟾N-钙黏着蛋白克隆8的EC5结构域互补的核糖探针进行原位杂交，确定了N-钙黏着蛋白在mRNA水平的表达模式。该序列部分在钙黏着蛋白基因家族中保守性最低，将与其他钙黏着蛋白交叉杂交的风险降至最低。在发育的最初阶段无法检测到N-钙黏着蛋白转录本。表达首先出现在神经板中，并在尾芽期的中枢神经系统中达到最高水平。从早期蝌蚪开始，表达量下降，因此在变态前的蛙脑中检测到非常微弱的信号。N-钙黏着蛋白在中枢神经系统内的表达并不均匀，一些区域如菱脑顶和嗅球表达较高水平的转录本。N-钙黏着蛋白存在于几种中胚层衍生物中，如脊索、前肾和心脏。然而，在肌节中几乎不存在，并且在分化后期出现在骨骼肌中。所有基板都表达高水平的N-钙黏着蛋白。非神经外胚层和内胚层始终呈阴性。在脑和心脏中，用与N-钙黏着蛋白假等位基因的两个拷贝在其5'非编码区相对应的探针观察到高水平的杂交，表明两个等位基因都被转录。
