Key Laboratory of Breeding Biotechnology and Sustainable Aquaculture (CAS), Qingdao, China; Laboratory for Marine Biology and Biotechnology, Qingdao Marine Science and Technology Center, Qingdao, China; School of Marine Science and Engineering, Qingdao Agricultural University, Qingdao 266000, China; Shandong Province Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China.
College of Fisheries, Huazhong Agricultural University, Wuhan 430070, China.
Int J Biol Macromol. 2024 Nov;279(Pt 1):135039. doi: 10.1016/j.ijbiomac.2024.135039. Epub 2024 Aug 27.
Seahorses exhibit the unique characteristic of male pregnancy, which incubates numerous embryos in a brood pouch that plays an essential role in enhancing offspring survivability. The pot-belly seahorse (Hippocampus abdominalis) possesses the largest body size among seahorses and is a significant species in Chinese aquaculture. In this study, we revealed the cytological and morphological characteristics, as well as regulatory mechanisms, throughout the entire brood pouch development in H. abdominalis. The brood pouch originated from the abdominal dermis, extending towards the ventral midline. As the dermal layers thicken, the inner epithelium folds, the stroma loosens, and vascularization occurs, culminating in the formation of the brood pouch. Furthermore, through transcriptomic analysis of brood pouches at various developmental stages, 8 key genes (tgfb3, fgf2, wnt7a, pgf, mycn, tln2, jund, ccn4) closely related to the development of brood pouch were identified in the MAPK, Rap1, TGF-β, and Wnt signaling pathways. These genes were highly expressed in the pseudoplacenta and dermal layers at the newly formed stage as examined by in situ hybridization (ISH). The angiogenesis, densification of collagen fibers, and proliferation of fibroblasts and endothelial cells in seahorse brood pouch formation may be regulated by these genes and pathways. Additionally, the expression of the androgen receptor gene (ar) was significantly upregulated during the formation of the brood pouch, and ISH confirmed the expression of the ar gene in the dermis and pseudoplacenta of the brood pouch, highlighting its role in the developmental process. Androgen and flutamide (androgen receptor antagonist) treatments significantly accelerated the formation of the brood pouch and completely inhibited its occurrence respectively, concomitant to the upregulated expression of differentially expressed genes involved above signaling pathways. These findings demonstrated that formation of the brood pouch is determined by androgen and the androgen receptor activates the above signaling pathways in the brood pouch through the regulation of fgf2, tgfb3, pgf, and wnt7a. Interestingly, androgen even induced the formation of the brood pouch in females. We firstly elucidated the formation of the seahorse brood pouch, demonstrating that androgens and their receptors directly induce the thickening, folding, and vascularization of the abdominal dermal layer into a placenta-like structure through multiple signaling pathways. These findings provide foundational insights to further exploring the evolution of male pregnancy and adaptive convergence in viviparity across vertebrates.
海马表现出独特的雄性怀孕特征，在育儿袋中孵化大量胚胎，育儿袋在提高后代存活率方面起着至关重要的作用。 短腹海马（Hippocampus abdominalis）是海马中体型最大的物种，也是中国水产养殖中的重要物种。 在这项研究中，我们揭示了短腹海马整个育儿袋发育过程中的细胞学和形态学特征以及调控机制。 育儿袋起源于腹部真皮，向腹中线延伸。 随着真皮层变厚，内上皮折叠，基质变松，血管化发生，最终形成育儿袋。 此外，通过对不同发育阶段的育儿袋进行转录组分析，在 MAPK、Rap1、TGF-β和 Wnt 信号通路中鉴定出 8 个与育儿袋发育密切相关的关键基因（tgfb3、fgf2、wnt7a、pgf、mycn、tln2、jund、ccn4）。 通过原位杂交（ISH）检查，这些基因在新形成的阶段在假胎盘和真皮层中高度表达。 血管生成、胶原蛋白纤维的密集化以及育儿袋形成中成纤维细胞和内皮细胞的增殖可能受到这些基因和途径的调节。 此外，雄激素受体基因（ar）在育儿袋形成过程中表达显著上调，ISH 证实 ar 基因在育儿袋真皮和假胎盘中的表达，强调其在发育过程中的作用。 雄激素和氟他胺（雄激素受体拮抗剂）处理分别显著加速和完全抑制育儿袋的形成，同时上述信号通路中的差异表达基因表达上调。 这些发现表明，育儿袋的形成取决于雄激素，雄激素通过调节 fgf2、tgfb3、pgf 和 wnt7a 激活育儿袋中的上述信号通路。 有趣的是，雄激素甚至诱导雌性形成育儿袋。 我们首次阐明了海马育儿袋的形成，表明雄激素及其受体通过多种信号通路直接诱导腹部真皮层变厚、折叠和血管化形成胎盘样结构。 这些发现为进一步探索雄性怀孕的进化和脊椎动物中胎生的适应性趋同提供了基础见解。
