de Jong, Danielle (2005) Characterisation of homologs of nervous system patterning genes in the staghorn coral, Acropora millepora (Cnidaria; Anthozoa; Scleractinia). PhD thesis, James Cook University.

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Abstract

The identification of a gene related to Drosophila ind/vertebrate Gsx and its expression in an axially-restricted manner implied that homologs of vnd/Nkx2.1 and msh/Msx - genes known to interact with ind, and with it pattern the DN axis of the nervous system might also be present in the staghorn coral, Acropora millepora. Genes of the vnd and Msx types were identified, and shown to expressed in axially-restricted patterns. However, it is difficult to relate the expression patterns of these cnidarian genes with their bilaterian counterparts, as unlike the ind/Gsx gene cnox-2Am, expression was not restricted to neurons. Preliminary investigation into the conservation of function of cnox-2Am in Drosophila using the P-element system suggested that cnox-2Am is capable of rescuing aspects of the ind null phenotype, which is consistent with conservation of function.

Two further genes were isolated from Acropora, which had sequence identity to genes involved in nervous system development in 'higher' animals. The first of these, cnox1Am, is related to the Hoxll/Tlx gene family, and also displays similarity to a predicted Drosophila gene, cg13424. Cnox1Am was shown to be expressed exclusively in the ectoderm of post-settlement polyps, in an axially restricted manner. Preliminary investigation into the expression pattern of cg13424 in Drosophila revealed expression in the maxillary bud in early stages (stage 9), and in the lateral transverse muscles of the body wall in later stages (stage 14 - 16). The second Acropora gene isolated (barhAm), is related to the Bar class genes which are involved in the patterning of anterior embryonic structures, in addition to their nervous system expression. The distribution of the barhAm transcript was also spatially restricted, and was expressed around the oral pore in pre- and post-settlement stages, and like cnox1Am, was not limited to a specific cell type.

The molecular basis of eye specification is conserved across the Bilateria, with eyeless/Pax-6 homologs specifying the early morphogenesis of eyes across the animal kingdom. Preliminary work in our laboratory implied that Acropora PaxCam might correspond to a Pax-6 precursor, implying that the eyes of cnidarians and bilaterians might be homologous. Consistent with this hypothesis, when fusion constructs of PaxC with the activation domain of EY were expressed in imaginal discs, ectopic eyes were generated. However, similar (but much weaker) phenotypes resulted from expression of PaxB/EY fusion proteins. The relationship between cnidarian and bilaterian Pax genes is therefore not simple.

Item ID:	26824
Item Type:	Thesis (PhD)
Keywords:	Acropora millepora; DNA; dorsal-ventral; drosophila; gene duplication; gene expression; genetics; homologous genes; homologs; homologues; nervous system; neurogenetics; patterning genes; staghorn corals; stony corals
Related URLs:	http://eprints.jcu.edu.au/6191/
Additional Information:	Publications arising from this thesis are available from the Related URLs field. The publications are: Hislop, Nikki R., de Jong, Danielle, Hayward, David C., Ball, Eldon E., and Miller, David J. (2005) Tandem organization of independently duplicated homeobox genes in the basal cnidarian Acropora millepora. Development Genes and Evolution, 215 (5). pp. 268-273.
Date Deposited:	09 May 2013 06:01
FoR Codes:	06 BIOLOGICAL SCIENCES > 0604 Genetics > 060405 Gene Expression (incl Microarray and other genome-wide approaches) @ 50% 06 BIOLOGICAL SCIENCES > 0604 Genetics > 060410 Neurogenetics @ 50%
SEO Codes:	96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 100%
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