The role of highly conserved non-coding DNA sequences in vertebrate development and evolution

Abstract

Comparisons between vertebrate genome sequences, from mammals to fishes, have revealed thousands of conserved non-coding elements (CNEs) that are associated with developmental genes. Interestingly, the vast majority of these CNEs cannot be found in invertebrate genomes by sequence homology. As many CNEs have been demonstrated to act as enhancers in-vivo, it has been postulated that CNEs represent gene regulatory elements with crucial roles in aspects of development that are shared between vertebrates. To trace the evolution of CNE sequences in vertebrates, a preliminary search for CNEs in the lamprey genome was conducted using the draft lamprey genome sequence. This thesis documents how the CNEs identified in lamprey have been used as a guide to ask questions about the function and evolution of CNEs in the vertebrate lineage. Through the combined use of comparative genomics and developmental biology techniques, including a newly developed reporter assay for sea lamprey embryos, crucial first steps have been taken toward systematically de-coding these ancient gene regulatory elements. Special attention is paid toward utilising the low sequence identity of lamprey CNEs for „phylogenetic footprinting‟, an approach which uncovers striking enrichment of CNEs for a set of motifs that are characteristic of Hox-regulated elements. These findings help to establish CNEs within a developmental and evolutionary context.