Gardiner-Garden M, Frommer M
Kanematsu Laboratories, Royal Prince Alfred Hospital, Camperdown, New South Wales, Australia.
J Mol Endocrinol. 1994 Jun;12(3):365-82. doi: 10.1677/jme.0.0120365.
DNA sequences of vertebrate genes which code for neural or neuroendocrine peptides were analysed in terms of CpG dinucleotide distribution and G+C content. The vast majority of the genes were found to contain a region with the sequence characteristics of a CpG island surrounding the 5' end. In mammalian species, the gene which codes for the neuroendocrine polypeptide pro-opiomelanocortin (POMC) was shown to be associated with two separate CpG islands: a 5' CpG island which surrounds the POMC transcription start site and a 3' CpG island which lies approximately 5 kb downstream, encompassing the third exon of POMC. Short POMC-related transcripts, known to be transcribed in the germline, were found to initiate from a promoter within the 3' CpG island. The start sites of the short POMC-related transcripts in mouse testis were mapped to the region coding for gamma MSH in exon 3, in a similar location to transcription start sites identified in other mammalian POMC genes. Similar short POMC-related transcripts were identified in both the mouse F9 embryonal carcinoma cell line and mouse embryonic stem cells, suggesting that transcription initiating within the third exon may occur very early in development. No short transcripts were detected by Northern blot hybridization in either Xenopus laevis testis or oocyte poly(A)+ RNA extracts. The Xenopus laevis POMC genes, A and B, were associated with neither a 5' nor a 3' CpG island. Hence, the presence of a 5' CpG island is not required for production of full-length transcripts from the Xenopus laevis POMC gene, but the presence of a 3' CpG island may be required for transcription to occur from the third exon.
对编码神经或神经内分泌肽的脊椎动物基因的DNA序列，根据CpG二核苷酸分布和G+C含量进行了分析。发现绝大多数基因在5'端周围含有一个具有CpG岛序列特征的区域。在哺乳动物物种中，编码神经内分泌多肽促肾上腺皮质激素原（POMC）的基因与两个独立的CpG岛相关：一个5'CpG岛围绕着POMC转录起始位点，另一个3'CpG岛位于下游约5 kb处，包含POMC的第三个外显子。已知在生殖系中转录的短POMC相关转录本，被发现从3'CpG岛内的一个启动子起始。小鼠睾丸中短POMC相关转录本的起始位点被定位到外显子3中编码γ-MSH的区域，与在其他哺乳动物POMC基因中鉴定的转录起始位点位置相似。在小鼠F9胚胎癌细胞系和小鼠胚胎干细胞中都鉴定出了类似的短POMC相关转录本，这表明在第三个外显子内起始的转录可能在发育早期就发生。在非洲爪蟾的睾丸或卵母细胞多聚腺苷酸（poly(A)+）RNA提取物中，通过Northern印迹杂交未检测到短转录本。非洲爪蟾的POMC基因A和B既不与5'也不与3'CpG岛相关。因此，非洲爪蟾POMC基因产生全长转录本不需要5'CpG岛的存在，但从第三个外显子进行转录可能需要3'CpG岛的存在。
