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Testing the homology of metazoan larvae using single cell sequencing data

Piovani, Laura; (2022) Testing the homology of metazoan larvae using single cell sequencing data. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Members of at least 15 animal phyla have a bi-phasic lifecycle composed of a pelagic larval stage which metamorphoses into a benthic adult. This lifecycle enables larvae to disperse in the ocean to colonise new environments. Although bi-phasic life cycles are widespread across Metazoa, it is unclear if marine larvae were present in the common ancestor or have evolved multiple times as an adaptation to a common selective pressure. Answering this question is fundamental if we are to reconstruct the lifecycle of the last common ancestor of animals. Many marine larvae are at least superficially similar, they are small, swim through beating of ciliated bands and sense the environment with an apical organ structure. Most animals with such larvae belong to the superclade of Lophotrochozoa and this thesis will concentrate on this group. To assess the homology of larvae, authors have compared the early development and expression profile of similar larval organs across phyla and shown that, generally, these are conserved. However, these studies only compared a handful of species and genes and a more thorough approach is needed. In this work I have used single cell sequencing to characterise the cells present in two lophotrochozoan marine larvae (mollusc’s trochophore larva and polyclad flatworms’ Mueller’s larva). I have performed in situ hybridisation and hybridisation chain reaction to identify cells belonging to different structures (including the ciliary bands and apical organ). Subsequently, I have compared the expression of orthologous genes in cell types of the two larvae. I have found that ciliary cells, neurons, muscles and proliferative cells co-express a large number of orthologous genes (>600) of which many are transcription factors (>30). 4 These results hint at a likely homology of lophotrochozoan larvae and set the basis to expand comparative work to more larvae across Bilateria and possibly Metazoa.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Testing the homology of metazoan larvae using single cell sequencing data
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2022. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Div of Biosciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Life Sciences > Div of Biosciences > Genetics, Evolution and Environment
URI: https://discovery.ucl.ac.uk/id/eprint/10142298
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