Müller T, Simoni M, Pekel E, Luetjens C M, Chandolia R, Amato F, Norman R J, Gromoll J
Institute of Reproductive Medicine of the University, Domagkstrasse 11, D-48129 Münster, Germany.
J Mol Endocrinol. 2004 Feb;32(1):115-28. doi: 10.1677/jme.0.0320115.
The pituitary gonadotrophins LH and FSH are responsible for regulation of gametogenesis in the testis and ovary. Chorionic gonadotrophin (CG), a third closely related glycoprotein hormone derived by gene duplication of the LHbeta gene and secreted by the placenta in primates, is essential for the rescue of the corpus luteum and maintenance of pregnancy. We have recently shown that marmoset (m) CGbeta mRNA is highly expressed in the pituitary of the common marmoset (Callithrix jacchus) and that LH is less active than human CG in activating the human LH receptor lacking exon 10. To investigate further which gonadotrophin is the actual ligand of the LH receptor (LHR) of the marmoset monkey that naturally lacks exon 10, we identified and characterised the genomic organisation of the mLHbeta gene and its expression. Intergenic PCR amplification of the region encompassing the mLHbeta and the mCGbeta genes revealed that, surprisingly, mCGbeta is located 20 kbp upstream of the LHbeta gene, whereas in other species the intergenic distance is approximately 2-3 kbp. Sequence analysis of the mLHbeta coding region showed 70% identity to mCGbeta and 90% identity to human LHbeta at the amino acid level. Both gonadotrophin beta subunits are present at the genomic level, but RT-PCR of pituitary and placental total RNA using specific oligonucleotides for mCGbeta and mLHbeta showed high expression of mCGbeta mRNA in both tissues, whereas LHbeta was expressed neither in the pituitary nor in the placenta. Thus mLHbeta mRNA is lacking in the marmoset pituitary. Immunohistochemistry of marmoset pituitaries showed that mCG was confined to the gonadotrophes, and partly co-localised in cells stained positively for FSH. Western blot analysis confirmed the presence of mCG in the pituitary. Northern blot analysis using mCGbeta as a probe displayed one transcript of 0.7 kb in the pituitary and detected two transcripts of 1.1 kb and 2 kb in the marmoset placenta. Our results suggest that, in the common marmoset, CG is the only gonadotrophin with luteinising function that is present in the pituitary. We postulate that, owing to an unknown mutational event in evolution, expression of mLH was completely abolished, and CG - which, unlike LH, acts normally even when exon 10 is missing from the LHR - took over its function.
垂体促性腺激素促黄体生成素（LH）和促卵泡生成素（FSH）负责调节睾丸和卵巢中的配子发生。绒毛膜促性腺激素（CG）是由LHβ基因通过基因复制衍生而来的第三种密切相关的糖蛋白激素，由灵长类动物的胎盘分泌，对挽救黄体和维持妊娠至关重要。我们最近发现，狨猴（m）CGβmRNA在普通狨猴（绢毛猴）的垂体中高度表达，并且在激活缺乏第10外显子的人LH受体方面，LH的活性低于人CG。为了进一步研究哪种促性腺激素是天然缺乏第10外显子的狨猴LH受体（LHR）的实际配体，我们鉴定并表征了mLHβ基因的基因组结构及其表达。对包含mLHβ和mCGβ基因的区域进行基因间PCR扩增，结果令人惊讶地发现，mCGβ位于LHβ基因上游20 kbp处，而在其他物种中，基因间距离约为2 - 3 kbp。mLHβ编码区的序列分析表明，在氨基酸水平上，它与mCGβ的同一性为70%，与人类LHβ的同一性为90%。两种促性腺激素β亚基在基因组水平上均存在，但使用针对mCGβ和mLHβ的特异性寡核苷酸对垂体和胎盘总RNA进行RT-PCR分析显示，mCGβmRNA在这两种组织中均高表达，而LHβ在垂体和胎盘中均未表达。因此，狨猴垂体中缺乏mLHβmRNA。狨猴垂体的免疫组织化学显示，mCG局限于促性腺细胞，并部分共定位于FSH染色阳性的细胞中。蛋白质印迹分析证实垂体中存在mCG。以mCGβ为探针进行Northern印迹分析，在垂体中显示出一条0.7 kb的转录本，在狨猴胎盘中检测到两条1.1 kb和两条2 kb的转录本。我们的结果表明，在普通狨猴中，CG是垂体中唯一具有促黄体生成功能的促性腺激素。我们推测，由于进化过程中发生了未知的突变事件，mLH的表达完全丧失，而CG（与LH不同，即使LHR中缺少第10外显子，它也能正常发挥作用）接管了其功能。
