Expanded expression of pro-neurogenic factor SoxB1 during larval development of gastropod suggests preadaptation to prolonged neurogenesis in Mollusca.

Introduction: The remarkable diversity observed in the structure and development of the molluscan nervous system raises intriguing questions regarding the molecular mechanisms underlying neurogenesis in . The expression of SoxB family transcription factors plays a pivotal role in neuronal development, thereby offering valuable insights into the strategies of neurogenesis.

Methods: In this study, we conducted gene expression analysis focusing on SoxB-family transcription factors during early neurogenesis in the gastropod . We employed a combination of hybridization chain reaction in situ hybridization (HCR-ISH), immunocytochemistry, confocal microscopy, and cell proliferation assays to investigate the spatial and temporal expression patterns of and from the gastrula stage to hatching, with particular attention to the formation of central ring ganglia.

Results: Our investigation reveals that demonstrates expanded ectodermal expression from the gastrula to the hatching stage, whereas expression of in the ectoderm ceases by the veliger stage. is expressed in the ectoderm of the head, foot, and visceral complex, as well as in forming ganglia and sensory cells. Conversely, is mostly restricted to the subepithelial layer and forming ganglia cells during metamorphosis. Proliferation assays indicate a uniform distribution of dividing cells in the ectoderm across all developmental stages, suggesting the absence of distinct neurogenic zones with increased proliferation in gastropods.

Discussion: Our findings reveal a spatially and temporally extended pattern of SoxB1 expression in a gastropod representative compared to other lophotrochozoan species. This prolonged and widespread expression of SoxB genes may be interpreted as a form of transcriptional neoteny, representing a preadaptation to prolonged neurogenesis. Consequently, it could contribute to the diversification of nervous systems in gastropods and lead to an increase in the complexity of the central nervous system in .