| dc.contributor.author | Handrigan, Gregory R. | en_US |
| dc.date.accessioned | 2014-10-21T12:36:49Z | |
| dc.date.available | 2006 | |
| dc.date.issued | 2006 | en_US |
| dc.identifier.other | AAINR19587 | en_US |
| dc.identifier.uri | http://hdl.handle.net/10222/54824 | |
| dc.description | A defining feature of modern anurans (frogs and toads) is their truncated vertebral column. In most, the axial skeleton comprises no more than 9 pre-sacral vertebrae, a single sacral vertebra, and, post-sacrally, the urostyle. Tadpoles from one anuran family, Megophryidae, deviate from this pattern in bearing up to 30 supernumerary vertebral centra in their tails. The osteology and ontogeny of the expanded caudal skeleton of megophryids varies widely within the family, but for all genera, supernumerary vertebrae are resorbed at metamorphosis, presumably by osteoclastic degradation. | en_US |
| dc.description | A potential molecular candidate underlying the expansion of the tail skeleton of megophryids and its reduced state in other anurans is the gene Pax1. Pax1-/- mutant mice exhibit loss of ventral vertebral elements, including centra and intervertebral discs. To explore a role for the gene in vertebral column development in anurans, I identified the Xenopus laevis ortholog, XlPax1, and characterized its developmental expression. The gene is strongly expressed in the pharyngeal endoderm and at lower levels in the sclerotomes, the precursors of vertebrae. This pattern is consistent with amniotes and corroborates a role for Pax1 in vertebral development in anurans. Given the observation of XlPax1 transcripts in the tail of X. laevis, however, I downplay Pax1's role in caudal vertebral agenesis in anurans. | en_US |
| dc.description | To explore the molecular basis for the axial truncation of the anuran presacral skeleton, I identified and characterized a second X. laevis gene, XlGdf11. In the mouse, Gdf11 has been implicated as a posteriorizing factor, regulating the expression boundaries of Hoxc genes and, upon genetic knock-out, causing dramatic posteriorization of the axial skeleton. In X. laevis, XlGdf11 is strongly expressed at the rostral end and also in the tail bud, the site of axial and paraxial tissue progenitors. Furthermore, genetic loss-of-function studies showed that XlGdf11 is important for the normal formation of the anteroposterior axis; however, the gene does not appear to act through its predicted downstream targets, the Hox genes, in carrying out this function. | en_US |
| dc.description | Collectively, these data underscore both the role of conserved molecular pathways in development and the potential of these pathways to generate novel morphologies. | en_US |
| dc.description | Thesis (Ph.D.)--Dalhousie University (Canada), 2006. | en_US |
| dc.language | eng | en_US |
| dc.publisher | Dalhousie University | en_US |
| dc.publisher | | en_US |
| dc.subject | Biology, Genetics. | en_US |
| dc.subject | Biology, Animal Physiology. | en_US |
| dc.title | A truncated axial skeleton: The evolutionary loss (and reappearance) of vertebrae in anurans. | en_US |
| dc.type | text | en_US |
| dc.contributor.degree | Ph.D. | en_US |
