Wood, Natalie Jane; (2020) Investigating the roles of neuropeptides in the development of the sea urchin, Strongylocentrotus purpuratus. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Neuropeptides are ancient signalling molecules that bind to receptors on target cells to induce a variety of growth, metabolic, reproductive and behavioural responses. At least 30 neuropeptide signalling systems were present in the common ancestor of bilaterians, and therefore neuropeptide signalling systems offer a good opportunity to characterise neuronal cell types and help determine the evolution of neuronal cell types and nervous systems. 38 neuropeptide precursor (NP) genes have so far been identified in the invertebrate deuterostome, the purple sea urchin, Strongylocentrotus purpuratus, but their function is largely unknown. Here I molecularly characterise and investigate the roles of NP signalling systems in the S. purpuratus embryo and larva. I first present the spatio-temporal data for NP genes and G-protein coupled receptors (GPCRs) genes during the development of S. purpuratus. QPCR and transcriptome data have revealed that almost all of these NP genes are expressed in the late larval stage, when cells differentiate. ISH data of these NP genes has revealed at least nine distinct populations of peptidergic neurons and showed that the sea urchin larval nervous system is more neurochemically complex than previously thought. Interestingly, some NP genes are also expressed in the pre-gastrula phase of embryogenesis, before cells differentiate. These early expressing NP genes are expressed in undifferentiated ectodermal and endodermal cells, suggesting that these signalling molecules may have a novel developmental role as well as a neuronal role. I also optimised CRISPR/Cas9 genome-editing in the sea urchin and used CRISPR/Cas9 and morpholino oligonucleotides to perturb the expression of an NP gene Sp-Thyrotropin releasing hormone (Sp-TRH) and its proven receptor. Here I show that the TRH neuropeptide signalling system acts as a local ectodermal cue, to regulate larval skeleton growth through VEGF and FGF signalling. This is the first study to investigate the roles of TRH signalling in a marine invertebrate larvae, which together with previous studies in adults reveals that the TRH signalling system is an ancient regulator of growth.

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