Takahashi Akiyoshi, Kobayashi Yuki, Moriyama Shunsuke, Hyodo Susumu
School of Fisheries Sciences, Kitasato University, Ofunato, Iwate 022-0101, Japan.
Gen Comp Endocrinol. 2008 May 15;157(1):41-8. doi: 10.1016/j.ygcen.2008.03.006. Epub 2008 Mar 10.
Proopiomelanocortin (POMC) is cleaved into small peptides, such as adrenocorticotropic hormone (ACTH), melanocyte-stimulating hormones (MSHs), and beta-endorphin (beta-END), by tissue-specific posttranslational processing in the corticotrophs of the pars distalis (PD) and melanotrophs of the neurointermediate lobe (NIL) of the pituitary. We examined the posttranslational processing of POMC in the pituitary of the banded houndshark Triakis scyllium by molecular cloning and subsequent mass spectrometric identification of the POMC-derived peptides in the pituitary extracts. One-fifth of the randomly selected clones from a Triakis pituitary cDNA library contained a cDNA encoding for POMC. Triakis prePOMC contained 4 MSHs and a single beta-END, as has been observed in case of other cartilaginous fish POMCs. These predicted hormonal segments were flanked by basic amino acid residues, which are the cleavage sites for the processing enzymes, i.e., protein convertases. Mass spectrometry was performed using PD (including most parts of the rostral and proximal PD) and NIL extracts to detect mass values corresponding to the POMC-derived peptides. Consequently, ACTH, beta-END, and the joining peptide (JP) were detected in the PD extract, while MSHs, processed beta-END, and some other POMC-derived peptides were identified in the NIL extract; however, neither acetylated alpha-MSH nor acetylated beta-END was detected in the latter. These tissue-specific POMC processing patterns are similar to those of the other vertebrate pituitaries; however, the absence of acetylated peptides suggests the lack of an acetylation system in the melanotrophs in the NIL of the Triakis pituitary.
阿黑皮素原（POMC）在垂体远侧部（PD）的促肾上腺皮质激素细胞和神经中间叶（NIL）的黑素细胞刺激素细胞中，通过组织特异性的翻译后加工，被切割成小肽，如促肾上腺皮质激素（ACTH）、黑素细胞刺激激素（MSHs）和β-内啡肽（β-END）。我们通过分子克隆以及随后对垂体提取物中POMC衍生肽的质谱鉴定，研究了带状星鲨Triakis scyllium垂体中POMC的翻译后加工过程。从Triakis垂体cDNA文库中随机选择的克隆中，五分之一包含编码POMC的cDNA。Triakis前阿黑皮素原含有4种黑素细胞刺激激素和单一的β-内啡肽，这与其他软骨鱼类的阿黑皮素原情况一致。这些预测的激素片段两侧是碱性氨基酸残基，它们是加工酶即蛋白转化酶的切割位点。使用PD（包括吻部和近端PD的大部分）和NIL提取物进行质谱分析，以检测与POMC衍生肽相对应的质量值。结果，在PD提取物中检测到了促肾上腺皮质激素、β-内啡肽和连接肽（JP），而在NIL提取物中鉴定出了黑素细胞刺激激素、加工后的β-内啡肽和一些其他POMC衍生肽；然而，在后者中未检测到乙酰化的α-黑素细胞刺激激素和乙酰化的β-内啡肽。这些组织特异性的POMC加工模式与其他脊椎动物的垂体相似；然而，乙酰化肽的缺失表明Triakis垂体NIL中的黑素细胞刺激素细胞缺乏乙酰化系统。
