Laboratory of Physiology, Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba, Japan.
Ibaraki Prefectural Oarai Aquarium, Oarai, Ibaraki, Japan.
Environ Microbiol Rep. 2024 Oct;16(5):e70025. doi: 10.1111/1758-2229.70025.
Vertebrate embryos are protected from bacterial infection by various maternally derived factors, yet little is known about the defence mechanisms in elasmobranchs. This study aimed to characterize the intracapsular environment of freshly laid eggs of the oviparous catshark (Scyliorhinus torazame) by investigating the microbial abundance and microbiota to understand its potential contribution to embryonic defence. The egg capsule of oviparous elasmobranchs is tightly sealed until pre-hatching, after which seawater flows into the capsule, exposing the embryos to the surrounding seawater. We found that early embryos were highly vulnerable to environmental pathogens, suggesting that the embryos are somehow protected from infection before pre-hatching. Indeed, the intracapsular environment of freshly laid eggs exhibited significantly low bacterial density, maintained until pre-hatching. Furthermore, the microbiome inside eggs just after oviposition differed markedly from those of rearing seawater and adult oviducal gland epithelia; these eggs were predominantly populated by an unidentified genus of Sphingomonadaceae. Overall, this study provides compelling evidence that early embryos of oviparous cloudy catshark are incubated in a clean intracapsular environment that potentially plays a significant role in embryonic development in oviparous elasmobranchs.
脊椎动物胚胎受到各种母体来源的因素的保护，免受细菌感染，但关于软骨鱼的防御机制知之甚少。本研究旨在通过研究微生物丰度和微生物组来描述卵生的猫鲨（Scyliorhinus torazame）刚产下的卵的囊内环境，以了解其对胚胎防御的潜在贡献。软骨鱼的卵囊在孵化前是紧密密封的，之后海水流入囊中，使胚胎暴露在周围的海水中。我们发现早期胚胎非常容易受到环境病原体的感染，这表明胚胎在孵化前以某种方式受到保护，免受感染。事实上，刚产下的卵的囊内环境中的细菌密度显著较低，并一直保持到孵化前。此外，卵刚产下时的内部微生物组与养殖海水和成年输卵管上皮的微生物组明显不同；这些卵主要由未鉴定的鞘氨醇单胞菌科的一个属定植。总的来说，这项研究提供了令人信服的证据，表明卵生的云纹猫鲨的早期胚胎在一个清洁的囊内环境中孵化，这可能在卵生软骨鱼的胚胎发育中发挥重要作用。
