Morphogenesis, or the development of tissues, structures, and organs, is at the heart of embryonic development. Morphogenesis is a complex, multi-tissue process that requires coordinated cellular communication, migration, and differentiation; due to this complexity, the mechanisms that underlie morphogenesis remain poorly understood. The sea urchin embryo is morphologically and genetically more simple than most other developmental model organisms, and is optically transparent, making it a highly tractable system in which to study morphogenetic processes. The sea urchin larval endoskeleton is a biomineral that is secreted by primary mesenchyme cells (PMCs). The PMCs ingress into the embryo and remain individual, mesenchymal cells that migrate into a stereotypic three-dimensional (3-D) pattern within the blastocoel, prefiguring the form of the ensuing skeleton, which they subsequently secrete. PMC positioning is directed by cues originating in the overlying ectoderm; however, the molecular identity of those cues has remained unknown. The work described in this dissertation combines systems-level approaches with in vivo 3-D spatial analysis to identify novel skeletal patterning genes and to define their functional roles in skeletal patterning. A transcriptomics-based screen identified numerous novel candidate skeletal patterning cues. Of those cues, two were further pursued for detailed functional studies. First, the sulfate transporter SLC26a2/7 (SLC) was found to promote ventral accumulation of sulfated proteoglycans that is both necessary and sufficient to attract PMCs to the ventral territory for ventral skeleton formation. Second, the enzyme 5-lipoxygenase (LOX) was found to be required for ventral and rotational skeletal patterning, and its product, 5(S)-HETE was found to be a chemoattractant for PMCs, thereby identifying a novel role for lipoxygenase enzymes in embryonic patterning and morphogenesis. Recent work from other groups has demonstrated that PMCs diversify their gene expression profiles during skeletal patterning, implying that PMC diversification is involved in skeletal patterning, likely as a response to locally distinct spatial cues. The studies herein identify Tbx2/3 and Pks2 as important PMC subset-specific genes whose spatial expression is modulated by SLC and LOX, respectively. Together, these results provide new mechanistic insights that define our molecular understanding of the regulation of sea urchin ventral skeletal patterning.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/42629 |
| Date | 25 May 2021 |
| Creators | Zuch, Daniel T. |
| Contributors | Bradham, Cynthia A. |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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