VERTEBRATE MAJOR TRANSITION; FIN
The extreme diversity lies in fish paired fins, which are adapted to each ecological lifestyle such as stingray or flying fish. Batoid fish (skates and rays) have extremely wide pectoral fins along the anteroposterior axis compared with other fish, while teleosts exhibit a small endochondral domain in their proximal fins. Apart from this spectacular diversity, fish fins are the evolutionary lineage leading to the tetrapod limb along with alterations to other body structures, which enabled fish to invade into land. Despite of the accumulation of the morphological description, gaps in the fossil records have hold back our understanding of underlying mechanisms. An advent of new technologies, however, has gradually make these problems within our reach.
GENETIC UNDERPINNINGS OF "LANDING"
During the water-to-land transition, a number of body structures were altered and new structures evolved as can be seen in the skull, jaw, shoulder, lung, appendages, and kidney. Whereas these morphological changes are central to the evolution of vertebrates, little research has been done to discern their developmental basis and identify the contributing evolutionary mechanisms. Bridging functional genomics, embryology and comparative anatomy, we answer long-standing and classical questions that could not be solved by either approach alone.
Functional genomics approach
Leveraged by new technology such as ATAC-sequencing (Assay for Transposes-Accesible Chromatin structure with high throughput sequencing; Gehrke AR et al. PNAS, 2015), 4C-sequencing, or ChIP-sequencing, comparative and functional genomics reveal responsible loci for major morphological transitions. Identification of candidate loci, in turn, prompts us to test their function by genetic manipulation.
Phenotype analysis with high energy CT scanner
An advent of new genetic tools enables us to modify target DNA loci. We investigate the phenotypes, consequences of genetic manipulations, with the CT scanner followed by segmentation of tissues and structures. The CT scanning comprehensively reveals morphological disparities between wild-type and mutant fish such as skeletal shape, innervation patterns or even volume of muscles.
Along with conducting experiments in the lab, we perform experiments at Marine Biological Laboratory (MA) during summer time and also collaborate with American Museum of Natural History (NY) to understand evolutionary mechanisms underlying vertebrate diversity.
Nakamura T et al. Digits and fin rays share common developmental histories. Nature. 2016 Aug 17;537(7619):225-228
Wood T and Nakamura T
Problems in Fish-to-Tetrapod Transition: Genetic Expeditions Into Old Specimens. Front. Cell Dev. Biol. 2018