Dupays Laurent, Mazurais David, Rücker-Martin Catherine, Calmels Thierry, Bernot Denis, Cronier Laurent, Malassiné André, Gros Daniel, Théveniau-Ruissy Magali
Laboratoire de Génétique et Physiologie du Développement, UMR 6545, Institut de Biologie du Développement de Marseille, Université de la Méditerranée, 13288 Marseille Cedex 9, France.
Gene. 2003 Feb 13;305(1):79-90. doi: 10.1016/s0378-1119(02)01229-5.
The human Cx40 gene (NT_004434.5) was sorted out from the GenBank database and as a result of a BLAST homology search, two ESTs (BE784549 from a human lung database, and BE732411 from a human placenta database) overlapping with the coding exon 2 sequence and upstream regions of the gene were identified. These ESTs correspond to two transcripts 1A and 1B, which diverge from each other in their 5' regions. The transcript 1A corresponds to the only transcript previously identified for the mouse and rat Cx40 genes; whereas the transcript 1B is a new transcript. The human Cx40 gene therefore comprises three exons: exon 1A (100 bp), exon 1B (132 bp) and coding exon 2, with the exons 1A and 1B at 14 and 1.3 kb of the exon 2, respectively. The expression of these transcripts is cell-type specific. Transcript 1A is expressed in endothelial cells. Its expression was demonstrated in human umbilical vein endothelial cells (HUVEC). Transcript 1B is expressed in placental cytotrophoblasts. Its expression was demonstrated in malignant trophoblastic cells, BeWo, JAR and JEG-3, and purified cytotrophoblasts from human first trimester placental tissues. Interestingly, both transcripts 1A and 1B are expressed in the right atrial appendages (RAA), although the cell-type expression of the two transcripts in this particular tissue has not yet been determined. Both transcripts were found to be expressed in the various heart regions investigated, where transcript 1B was found to always occur rarely in comparison with transcript 1A. Transcripts 1A and 1B are both more abundant in the atria than in the ventricles. Luciferase reporter gene assays demonstrated that two genomic regions containing the exons 1A and 1B induced a cell-type specific expression. The 1.2 kb sequence, containing the exon 1A, induced an increase of the luciferase activity in HUVEC; whereas the 1.9 kb sequence, containing the exon 1B, induces an increase of expression of the luciferase activity in BeWo cells. The DNA sequence upstream of the exon 1A contains SP1 binding sites, but no TATA- or CAAT-box; whereas the region upstream of the exon 1B is preceded by three CAAT-boxes. Thus, in contrast to the mouse and rat Cx40 genes, the human Cx40 gene organized in three exons and generates two transcripts, which are cell-type specific.
从GenBank数据库中筛选出人类Cx40基因（NT_004434.5），经BLAST同源性搜索，鉴定出两个与该基因编码外显子2序列及上游区域重叠的EST（来自人类肺数据库的BE784549和来自人类胎盘数据库的BE732411）。这些EST对应于两个转录本1A和1B，它们在5'区域彼此不同。转录本1A对应于先前为小鼠和大鼠Cx40基因鉴定出的唯一转录本；而转录本1B是一个新的转录本。因此，人类Cx40基因包含三个外显子：外显子1A（100 bp）、外显子1B（132 bp）和编码外显子2，外显子1A和1B分别位于外显子2的14 kb和1.3 kb处。这些转录本的表达具有细胞类型特异性。转录本1A在内皮细胞中表达，已在人脐静脉内皮细胞（HUVEC）中得到证实。转录本1B在胎盘细胞滋养层细胞中表达，已在恶性滋养层细胞BeWo、JAR和JEG - 3以及来自人类孕早期胎盘组织的纯化细胞滋养层细胞中得到证实。有趣的是，转录本1A和1B在右心耳（RAA）中均有表达，尽管尚未确定这两个转录本在该特定组织中的细胞类型表达情况。在研究的各个心脏区域均发现这两个转录本都有表达，其中发现转录本1B与转录本1A相比总是很少出现。转录本1A和1B在心房中的表达均比心室中更丰富。荧光素酶报告基因检测表明，包含外显子1A和1B的两个基因组区域诱导了细胞类型特异性表达。包含外显子1A的1.2 kb序列在HUVEC中诱导荧光素酶活性增加；而包含外显子1B的1.9 kb序列在BeWo细胞中诱导荧光素酶活性表达增加。外显子1A上游的DNA序列包含SP1结合位点，但没有TATA盒或CAAT盒；而外显子1B上游区域之前有三个CAAT盒。因此，与小鼠和大鼠Cx40基因不同，人类Cx40基因由三个外显子组成并产生两个转录本，它们具有细胞类型特异性。
