Misaki Marine Biological Station, School of Science, The University of Tokyo, Misaki, Miura, Kanagawa, 238-0225, Japan.
Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Hongo, Bunkyo, Tokyo, 113-0033, Japan.
Sci Rep. 2023 Nov 22;13(1):19419. doi: 10.1038/s41598-023-46358-8.
Benthic annelids belonging to the family Syllidae (Annelida, Errantia, Phyllodocida) exhibit a unique reproduction mode called "schizogamy" or "stolonization", in which the posterior body part filled with gametes detaches from the original body, as a reproductive unit (stolon) that autonomously swims and spawns. In this study, morphological and histological observations on the developmental processes during stolonization were carried out in Megasyllis nipponica. Results suggest that the stolon formation started with maturation of gonads, followed by the formation of a head ganglion in the anteriormost segment of the developing stolon. Then, the detailed stolon-specific structures such as stolon eyes and notochaetae were formed. Furthermore, expression profiles of genes involved in the anterior-posterior identity (Hox genes), head determination, germ-line, and hormone regulation were compared between anterior and posterior body parts during the stolonization process. The results reveal that, in the posterior body part, genes for gonadal development were up-regulated, followed by hormone-related genes and head-determination genes. Unexpectedly, Hox genes known to identify body parts along the anterior-posterior axis showed no significant temporal expression changes. These findings suggest that during stolonization, gonad development induces the head formation of a stolon, without up-regulation of anterior Hox genes.
底栖环节动物 Syllidae 科（环节动物门、游走亚门、叶须虫目）表现出一种独特的繁殖方式，称为“裂殖生殖”或“匍匐生殖”，其中充满配子的后体部分从原始体上分离出来，成为一个自主游动和产卵的生殖单位（匍匐体）。本研究对日本沙蚕 Megasyllis nipponica 的匍匐生殖发育过程进行了形态学和组织学观察。结果表明，匍匐体的形成始于性腺的成熟，然后在前发育匍匐体的最前段形成一个头部神经节。然后，形成了详细的匍匐体特有的结构，如匍匐体眼和刚毛。此外，还比较了在匍匐生殖过程中前后体部分的涉及体前后身份（Hox 基因）、头部确定、生殖系和激素调节的基因的表达谱。结果表明，在后体部分，性腺发育相关基因上调，其次是激素相关基因和头部确定基因。出乎意料的是，沿体前后轴识别体节的 Hox 基因没有表现出明显的时间表达变化。这些发现表明，在匍匐生殖过程中，性腺发育诱导匍匐体的头部形成，而不向上调节前 Hox 基因。
