Notch signaling in leech neurogenesis: expression patterns and functional insights in the Glossiphoniid leech Helobdella austinensis.

The Notch signaling pathway is one of the most evolutionarily conserved pathways, playing a crucial role in juxtacrine signaling between adjacent cells. Although previous studies have characterized Notch signaling in diverse models, its function in the lophotrochozoan animals is largely not understood and is only partially identified in early-stage embryos. To address this gap, we reaffirmed the expression of Notch homolog, including downstream components, in the organogenesis of the Glossiphoniid leech, Helobdella austinensis. We analyze the spatial and temporal expression patterns of the Notch receptor (Hau-notch1), ligands (Hau-delta and Hau-jagged), and transcription factors (Hau-hes and Hau-hey) from embryonic stages 8-11. Notch transcripts are expressed in the germinal plate and segmental precursor cells at stage 8, with expression expanding to the somites, ventral and supraesophageal ganglia by stage 9. In organogenesis stages (stages 9-11), Notch components are expressed in the anterior and posterior suckers, proboscis, and ventral ganglia, indicating their role in nerve differentiation. Furthermore, blocking of Notch signaling by DAPT (N-[N-(3, 5-difluorophenacetyl)-l-alanyl]-s-phenylglycine t-butyl ester) leads to the disruption of nerve formation with downregulation of transcription factors (Hau-hes and Hau-hey). Our findings provide insights into the conserved mechanisms of Notch signaling in bilaterian neural development, contributing to a deeper understanding of evolutionary developmental biology.