The function of the Notch signalling pathway in pattern formation and head regeneration in Hydra

Pan, Qin (2025): The function of the Notch signalling pathway in pattern formation and head regeneration in Hydra. Dissertation, LMU München: Fakultät für Biologie

Abstract

The Notch signalling pathway is a highly conserved cell-to-cell communication mechanism in animals. Notch ligands, such as Delta, can regulate the activity of Notch receptors by transactivation in neighbouring cells or cis inhibition within the same cell. This dual regulatory mechanism makes Notch signalling essential for establishing boundaries. In Hydra, previous studies using the presenilin inhibitor DAPT have shown that Notch signalling is crucial for defining the parent-bud boundary and for head regeneration following apical decapitation. In the first part of this thesis (Pan, Mercker et al. 2024), Notch transgenic Hydra strains were established to further investigate the function of the Notch signalling pathway. These included NICD-overexpressing and Notch knockdown transgenic Hydra strains. NICD-overexpressing transgenic Hydra exhibited downregulation of predicted Notch target genes and displayed “Y-shaped” polyps, a phenotype also observed in DAPT-treated Hydra. This suggests that NICD-overexpression exerts a dominant-negative effect. Additional phenotypes observed in NICD-overexpressing Hydra included “ectopic tentacles”, “two-headed”, and “multiple heads”. Notch-knockdown Hydra exhibited similar phenotypes, except for the “multiple heads” form. Instead, an additional “two feet” phenotype was observed. Furthermore, both NICD-overexpressing and Notch-knockdown Hydra displayed abnormal head regeneration phenotypes following apical or middle gastric decapitation. These findings confirm that the Notch signalling pathway plays a critical role in body-axis patterning and head regeneration in Hydra. In the second part of this thesis (Moneer, Siebert et al. 2021), a transcriptome analysis of DAPT-treated Hydra was conducted, identifying 666 Notch-responsive genes with defined expression patterns in Hydra. Among these, genes associated with nematogenesis and head patterning were predominantly downregulated. In addition to HyHes, Sp5 and HyAlx were identified as the most promising direct targets of Notch signalling. Furthermore, an upregulated transcriptional factor, HyKayak, was identified, which shows expression in ectodermal head cells and battery cells. This led to the hypothesis that HyKayak might serve as a Notch-dependent regulator of HyWnt3, potentially acting as an inhibitor of HyWnt3. The third part (Steichele, Sauermann et al. 2025) describes that Hydra head regeneration involves two distinct processes: hypostome regeneration and tentacle patterning. The Notch signalling pathway was found to play a crucial role in regulating the regenerating sequence of these processes. Following apical decapitation, Notch signalling appeared to suppress tentacle fate, probably by inhibiting BMP5/8b expression, thereby promoting hypostome fate through the activation of HyWnt3. Further experiments confirmed that the loss of HyKayak function, either through shRNA-knockdown or pharmacological treatment, resulted in upregulated expression of HyWnt3, suggesting that HyKayak can repress the expression of HyWnt3.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Keywords: the Notch signalling pathway, Hydra
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 570 Biowissenschaften, Biologie
• Fakultäten: Fakultät für Biologie
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 15. Juli 2025
• 1. Bericht­erstatter:in: Böttger, Angelika