Project description:Whereas the gill chambers of extant jawless vertebrates (lampreys and hagfish) open directly into the environment, jawed vertebrates have evolved skeletal appendages that promote the unidirectional flow of oxygenated water over the gills. A major anatomical difference between the two jawed vertebrate lineages is the presence of a single operculum covering a large common gill cavity in bony fishes versus separate covers for each gill chamber in cartilaginous fishes. Here we find that these divergent gill cover patterns correlate with the pharyngeal arch expression of Pou3f3 orthologs, and we identify a deeply conserved Pou3f3 arch enhancer that is present in nearly all jawed vertebrates but undetectable in lampreys. Despite only minor sequence differences, bony fish and cartilaginous fish versions of this enhancer are sufficient to drive the respective single versus multiple gill arch expression. In zebrafish, loss of Pou3f3 gene function or its conserved enhancer disrupts gill cover formation. Conversely, forced expression of Pou3f3b in the gill arches generates ectopic skeletal elements reminiscent of the multiple gill covers of cartilaginous fish. Emergence and modification of this ancient Pou3f3 enhancer may thus have contributed to the acquisition and diversification of gill covers during early gnathostome evolution.
Project description:Homologous vertebrate tissues express a highly conserved set of transcribed genes; paradoxically, expression of tRNAs that are required to translate mRNAs into proteins have been reported to be divergent. To resolve this paradox, we mapped the genome-wide occupancy of pol III in primary tissues isolated from six mammals. We confirmed that the specific tRNA genes bound by pol III, as well as the extent and stability of binding, can vary substantially among mammalian tissues, and we discovered that this divergence is far greater between species. We combined pol III occupancy from genomically discrete tRNA loci into collective binding into isoacceptor classes and then into amino acid-based isotype classes, and at each step we found increasing conservation. At the level of amino acid isotypes, pol III binding is almost invariant among all the tissues and species profiled. Thus, the basal transcriptional machinery is constrained collectively in its synthesis of functional tRNA isotypes, despite rapid divergence of polymerase binding to specific tRNA genes. Part of experiment series: RNA-Seq E-MTAB-424, ChIP-Seq E-MTAB-957
Project description:We address the evolutionary origins of vertebrate pluripotency by comparing the development of neural crest and blastula stem cells using representatives from both jawed (Xenopus) and jawless (lamprey) vertebrates.