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dc.contributor.authorWright, Alison Juliaen
dc.date.accessioned2018-01-31T11:40:38Z
dc.date.available2018-01-31T11:40:38Z
dc.date.issued2004en
dc.identifier.urihttp://hdl.handle.net/1842/27710
dc.description.abstracten
dc.description.abstractThe NK homeobox gene family comprises an extensive collection of transcription factors which have been shown to play pivotal roles in cell-fate specification and organogenesis. Murine Bapxl (Nkx3.2) was isolated as an evolutionarily conserved homologue of Drosophila bagpipe (NK3) which specifies the visceral mesoderm giving rise to gut musculature. A role for Bapxl in gut development has been conserved to mammals, where it would appear to be required both to specify the identity and to direct asymmetric growth of the spleno-pancreatic mesenchyme. Epithelial-mesenchymal signalling is an essential part of gut organogenesis, however the precise role of the mesenchyme is poorly understood and critical time points for its presence remain unknown. Initial investigations to probe the importance of the mesenchyme focussed on attempts to ablate this specific cell population by directing a toxic phenotype to Bapxl -expressing cells. A recombineering approach using Bapxlcontaining PACs was employed to generate the targeting construct, however inability to modify the Bapxl locus necessitated adoption of an alternative approach.en
dc.description.abstractThe regulatory elements responsible for directing tissue-specific Bapxl expression have not yet been determined, therefore to pursue investigation of the role of the mesenchyme in gut development would require elucidation of a gut-specific Bapxl enhancer. Comparative sequence analysis between human, mouse and fish identified two candidate control elements, termed ProxB and DistB, which reside 1 lkb and 18kb respectively downstream of Bapxl. ProxB constitutes a short region of high sequence conservation between human and mouse, within which 180bp was also found to be conserved to zebrafish. DistB encompasses a more extensive 8kb genomic region highly conserved in mammals. Both the ProxB putative regulatory element and a 2kb subfragment of DistB named DistB 1 were cloned into a LacZ reporter construct and assayed for enhancer activity in transgenic mice. Both elements exhibited tissue-specific enhancer capacities with ProxB-driven expression initially confined to the mandibular portion of the first branchial arch and later detected in Meckel's cartilage and the middle ear. Detailed analysis of the expression pattern and comparison to evolutionarily conserved expression domains provides good evidence that ProxB constitutes a regionspecific Bapxl regulatory element. DistB 1 appears to be capable of directing expression to several different tissues, notably including the digits where it closely resembles endogenous Bapxl expression. Further parallels between the DistB 1 and Bapxl expression domains suggest that this element may also contribute to the endogenous regulation of Bapxl.en
dc.description.abstractPhenotypic comparisons between Bapxl null mutant mice and their wildtype counterparts have contributed significantly to knowledge of the wildtype function of the gene. Within the developing gut, distinct molecular boundaries are apparent. Bapxl demarcates the domain of the posterior stomach and asplenic null mutants attest to its being essential for formation of the spleen. Various gut markers were employed to study the disruption of both gut development and defined molecular domains in the absence of Bapxl. A marked difference in Sonic hedgehog (Shh) expression was observed in mutant guts, revealing a fusion of the upper duodenum to the posterior stomach to contribute to the enlarged stomach phenotype. Furthermore, Shh expression was detected in an abnormal branch emanating from the duodenum and extending alongside the posterior stomach thus exposing a novel phenotypic manifestation of the mutation.en
dc.description.abstractA novel anatomical structure, the splanchnic mesothelial plate (SMP) has been implicated in leftward mesenchymal growth during spleen morphogenesis. Cells within the SMP express Bapxl, without which leftward growth is disrupted and asplenia results. Prompted by these observations, a description of spleen development was undertaken to closely examine the precise origin and subsequent morphogenesis of this organ. Expression of the spleen marker Hoxl 1 was followed in dissected guts within a defined developmental window. The marked morphological transformation from a small domain of Hoxl/-expressing cells posterior to the stomach to an extensive layer flanking the dorsal mesogastrium is described herein. This work prompts questions as to whether a wave of cell-cell signalling or cell migration is responsible for the observed development of the spleen.en
dc.publisherThe University of Edinburghen
dc.relation.isreferencedbyAlready catalogueden
dc.subjectAnnexe Thesis Digitisation Project 2017 Block 16en
dc.titleGut development: the regulation, evolution and function of Bapx1en
dc.typeThesis or Dissertationen
dc.type.qualificationlevelen
dc.type.qualificationnamePhD Doctor of Philosophyen


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