Department of Biology, Electron Microscopy Laboratory, University of Victoria, Victoria, BC, V8W 3N5, Canada.
Department of Biology, University of Victoria, Victoria, BC, V8W 3N5, Canada.
Histochem Cell Biol. 2023 Dec;160(6):517-539. doi: 10.1007/s00418-023-02227-z. Epub 2023 Aug 11.
Although it is known that the whitefish, an ancient salmonid, expresses three distinct gonadotropin-releasing hormone (GnRH) forms in the brain, it has been thought that the later-evolving salmonids (salmon and trout) had only two types of GnRH: GnRH2 and GnRH3. We now provide evidence for the expression of GnRH1 in the gonads of Atlantic salmon by rapid amplification of cDNA ends, real-time quantitative PCR and immunohistochemistry. We examined six different salmonid genomes and found that each assembly has one gene that likely encodes a viable GnRH1 prepropeptide. In contrast to both functional GnRH2 and GnRH3 paralogs, the GnRH1 homeolog can no longer express the hormone. Furthermore, the viable salmonid GnRH1 mRNA is composed of only three exons, rather than the four exons that build the GnRH2 and GnRH3 mRNAs. Transcribed gnrh1 is broadly expressed (in 17/18 tissues examined), with relative abundance highest in the ovaries. Expression of the gnrh2 and gnrh3 mRNAs is more restricted, primarily to the brain, and not in the gonads. The GnRH1 proximal promoter presents composite binding elements that predict interactions with complexes that contain diverse cell fate and differentiation transcription factors. We provide immunological evidence for GnRH1 peptide in the nucleus of 1-year-old type A spermatogonia and cortical alveoli oocytes. GnRH1 peptide was not detected during other germ cell or reproductive stages. GnRH1 activity in the salmonid gonad may occur only during early stages of development and play a key role in a regulatory network that controls mitotic and/or meiotic processes within the germ cell.
虽然已知白鲑鱼（一种古老的鲑鱼）在脑中表达三种不同的促性腺激素释放激素（GnRH）形式，但人们一直认为后来进化的鲑鱼（鲑鱼和鳟鱼）只有两种 GnRH：GnRH2 和 GnRH3。我们现在通过 cDNA 末端快速扩增、实时定量 PCR 和免疫组织化学提供了大西洋鲑鱼性腺中 GnRH1 表达的证据。我们检查了六个不同的鲑鱼基因组，发现每个组装都有一个可能编码可行 GnRH1 前肽的基因。与功能性 GnRH2 和 GnRH3 同源物不同， GnRH1 同系物不再表达激素。此外，可行的鲑鱼 GnRH1 mRNA 仅由三个外显子组成，而不是构建 GnRH2 和 GnRH3 mRNA 的四个外显子。转录的 gnrh1 广泛表达（在检查的 17/18 种组织中），相对丰度在卵巢中最高。 gnrh2 和 gnrh3 mRNA 的表达更为局限，主要在大脑中，而不在性腺中。 GnRH1 近端启动子呈现出复合结合元件，预测与包含多种细胞命运和分化转录因子的复合物相互作用。我们提供了 GnRH1 肽在 1 岁 A 型精原细胞和皮质肺泡卵母细胞核中的免疫证据。在其他生殖细胞或生殖阶段未检测到 GnRH1 肽。 GnRH1 活性在鲑鱼性腺中可能仅发生在发育的早期阶段，并在控制生殖细胞有丝分裂和/或减数分裂过程的调节网络中发挥关键作用。
