Takahashi Akiyoshi, Nakata Osamu, Kasahara Makoto, Sower Stacia A, Kawauchi Hiroshi
Laboratory of Molecular Endocrinology, School of Fisheries Sciences, Kitasato University Sanriku, Ofunato, Iwate, Japan.
Gen Comp Endocrinol. 2005 Nov;144(2):174-81. doi: 10.1016/j.ygcen.2005.05.002. Epub 2005 Jun 24.
Gnathostomes express a common proopiomelanocortin (POMC) gene in the pars distalis (PD) and the pars intermedia (PI) of the pituitary gland. In contrast, the sea lamprey Petromyzon marinus expresses one distinct gene in each lobe; proopiocortin (POC) encoding adrenocorticotropic hormone (ACTH) and beta-endorphin (END) is expressed in the PD and proopiomelanotropin (POM) encoding melanophore-stimulating hormone (MSH), and a different beta-END is expressed in the PI. We characterized the genomic structure of the sea lamprey POC and POM genes including their 5'-flanking regions. Both genes have two introns at positions similar to those of gnathostomes. Each exon encodes genetic information seen in the gnathostome POMC gene: exon 1 encodes an untranslated nucleotide sequence, exon 2 encodes a signal peptide and the N-terminal short part of POC or POM, and exon 3 encodes all other parts including ACTH, MSHs or beta-END. Intron-A of POM (2289 bp) is six times longer than that of POC (379 bp). The POM intron-A has three transposon-like sequences (TnL-1, -2, -3), the total length of which is 1781 bp, suggesting that it has expanded via the insertion of TnLs. The 5'-flanking region of the POC gene contains two TATA boxes, a CCAAT box, eight E boxes, STAT, RAIE, and one binding site each for Ptx1, Pit-1, and Tpit. The POM gene contains four TATA boxes, eight E boxes, three STATs, two RAIEs, two CRE-like elements, and one binding site for Pit1. However, there is virtually no similarity between the two genes in the distribution of the elements. The transcriptional regulation of POC and POM may have diverged with the functional differentiation of the two genes.
有颌类动物在垂体远侧部（PD）和中间部（PI）表达一种共同的阿黑皮素原（POMC）基因。相比之下，海七鳃鳗（Petromyzon marinus）在每个叶中表达一个不同的基因；编码促肾上腺皮质激素（ACTH）和β-内啡肽（END）的促阿片皮质素（POC）在PD中表达，编码促黑素（MSH）的促阿片黑素细胞刺激素（POM）以及另一种不同的β-END在PI中表达。我们对海七鳃鳗POC和POM基因的基因组结构进行了表征，包括它们的5'侧翼区域。这两个基因在与有颌类动物相似的位置都有两个内含子。每个外显子编码有颌类动物POMC基因中可见的遗传信息：外显子1编码一个未翻译的核苷酸序列，外显子2编码一个信号肽和POC或POM的N端短部分，外显子3编码包括ACTH、MSH或β-END在内的所有其他部分。POM的内含子A（2289 bp）比POC的内含子A（379 bp）长六倍。POM内含子A有三个转座子样序列（TnL-1、-2、-3），其总长度为1781 bp，表明它是通过TnL的插入而扩展的。POC基因的5'侧翼区域包含两个TATA框、一个CCAAT框、八个E框、STAT、RAIE以及Ptx1、Pit-1和Tpit的各一个结合位点。POM基因包含四个TATA框、八个E框、三个STAT、两个RAIE、两个CRE样元件以及Pit1的一个结合位点。然而，这两个基因在元件分布上几乎没有相似性。POC和POM的转录调控可能随着这两个基因的功能分化而发生了分歧。
