ORCID

Abstract

The apical organ is a key sensory structure in marine invertebrate larvae that is involved in sensory processing and neural coordination, thereby influencing larval locomotion, settlement, and metamorphosis. This thesis explores the evolution, development, and function of the apical organ and wider apical domain in cnidarian larvae, with a particular focus on Nematostella vectensis. As an early-branching metazoan, N. vectensis is a unique model for studying evolution of the apical organ, and subsequently the origins of the nervous system. Through generating tissue-specific transcriptomes and integrating this data with an existing single-cell RNA sequencing dataset, this research identified a distinct neuronal signature and at least six cell types comprising the apical domain of N. vectensis, uncovering the molecular complexity of this sensory organ.Comparative analyses of tissue-specific transcriptomes across other cnidarian species revealed a high level of conservation of anteroposterior patterning genes between N. vectensis and stony corals, however some critical genes involved in apical organ formation were absent from the stony coral apical transcriptomes. Further, a significant divergence in the expression of apical domain genes between anthozoans and medusozoans was uncovered. Moreover, the expression of 245 unique ciliary genes in the N. vectensis apical transcriptome, the only species studied in this thesis to produce larvae with an apical tuft, supports convergent evolution of the apical tuft in the Cnidaria and highlights the specialised nature of the N. vectensis apical organ.Finally, we delved into the molecular composition and functional role of the apical tuft in N. vectensis larvae. Perturbation of the transcription factor FoxJ1 identified the criticality of this gene for the formation of the apical tuft, with its knockdown arresting apical tuft development and resulting in delayed metamorphosis.However, as metamorphosis was still successful in the absence of an apical tuft, we concluded that the tuft plays a facilitatory role in the larval-polyp transition.Overall, these results presented in this thesis advance our understanding of how the apical organ evolved in the Cnidaria, providing new insights into both the conserved regulatory networks and species-specific pathways that underpin its development. Further, this research eludes to a more enigmatic and potentially complex role of the apical organ and apical tuft in regulating metamorphosis, which requires further investigation to solve.

Awarding Institution(s)

University of Plymouth

Supervisor

Vengamanaidu Modepalli, Manuela Truebano, Michael Cunliffe

Keywords

Apical organ, Nematostella vectensis, Cnidaria, Larval development, Metamorphosis, Transcriptomics, Evolution

Document Type

Thesis

Publication Date

2025

Embargo Period

2025-07-10

Deposit Date

July 2025

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