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Dissertation submitted to the Faculty of Science, University of the Witswatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. May 2015 in Johannesburg / Claudins are a large gene family found in all vertebrates. Claudins encode tetraspan membrane proteins, involved in the structure and function of the tight junctions. This association of cells leads to the formation of the epithelial sheet which is involved in many functions such as embryo morphogenesis. The NCBI database shows 27 claudins identified in humans; 23 in mice and 17 in Xenopus. This suggests that an increase in gene family size may correlate with the evolution of more complex vertebrates. In this study claudins from the most basal extant vertebrate, the sea lamprey, were investigated. RNA used to build up the lamprey genome by Jeramiah Smith (Smith et al., 2012), was used for lamprey claudin sequences. Additionally this study identified 2 more claudins (Cldn B & Cldn F). The phylogenetic tree constructed using claudins from higher vertebrate model organisms and the invertebrates Ciona intestinalis and Drosophila melanogaster; showed that lamprey claudins are evolutionarily more distantly related to their orthologs in higher vertebrates. Furthermore some claudins in lamprey did not show any homologs in higher vertebrates and vice versa, indicating the emergence of novel members in higher vertebrates. However lamprey Cldn A was found to be homologous to CLDN 3 in higher vertebrates. This is interesting since CLDN 3 is involved in the development of two vertebrate specific traits; one of which is the ear placode. Thus Cldn A (renamed Cldn 3B), was made a focus of this study. RNA in situ hybridization using probes designed from individual UTRs showed localised expression of Cldn 3B in the ear placode, pharyngeal pouch, pericardial cavity and the fin fold whereas Cldn B (renamed Cldn 8B) was mostly expressed in the pharyngeal pouch and ear placode much like its orthologs in higher vertebrates. Knockout experiments showed that Cldn 3B is involved in sealing and expansion of the ear placode and pharyngeal arches during development whereas Cldn 8B is involved in determining ear placode development. Thus claudins are seen to be heavily involved in the morphology of vertebrate specific traits therefore an expansion in this gene family would affect the complexity of vertebrates during evolution.

Thesis (M.S.)--Michigan State University, Dept. of Fisheries and Wildlife, 2006. / Title from PDF t.p. (viewed on Nov. 20, 2008) Includes bibliographical references (p. 89-95). Also issued in print.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1975. / Typescript. Vita. Description based on print version record. Includes bibliographical references (leaves 135-144).

Lic.-avh. (sammanfattning) Stockholm : Karolinska institutet, 2007. / Härtill 2 uppsatser.

Thesis (Ph.D.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on April 27, 2009) Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references (leaves 291-307). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references (leaves 291-307). Also available on the Internet.

Thesis (M.A.)--University of Missouri-Columbia, 2008. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 12, 2009) Includes bibliographical references.