The Evolution of Evo-Devo

Evo-devo has seen waves of excitement following technological advances since its early days in the late 19th century, when scientists began searching for clues about evolutionary trends by peering into slices of embryos using histology and microscopy. Interest in evo-devo piqued again with advances in molecular biology that allowed scientists to piece together information about genes and gene expression during development. In recent years, the field has experienced yet another rebirth as tools for editing and sequencing genomes have advanced alongside new microscopy techniques. Despite evo-devo’s long history, “there are old questions that still remain largely unanswered,” explains Gillis.

The main cast of characters in developmental biology research tends to include animals like mice, chickens, zebrafish, and frogs. Evo-devo researchers often  compare these popular research organisms to less mainstream ones, such as the little skate (Leucoraja erinacea). In the past, skates have been used to study how fins evolved into limbs by researchers in the lab of Neil Shubin, evolutionary biologist at the University of Chicago and former interim director of the MBL. Gillis, a former PhD student of Shubin’s, has found a new role for the little skate in understanding how the jaw develops.

Gillis and his former student Christine Hirschberger, who is currently a postdoctoral research associate at the University of Cambridge, published a paper in Development this week that found a small structure at the back of the skate jaw that gives clues about how jaws may have evolved. The structure in question, the pseudobranch, closely resembles a gill, and shares cell types and gene expression features with gills, which hints that the jaw likely evolved from the same structures that create gills.

The pseudobranch was also the subject of a study in zebrafish by Mathi Thiruppathy, graduate student in the lab of Gage Crump at the University of Southern California and student in the MBL Embryology course this summer. In addition to using similar techniques as Hirschberger and Gillis, Thiruppathy’s group was able to use more genetic tools. They employed mutant gill-less zebrafish to show that a gene integral to the development of the gills is also essential for proper pseudobranch development, further supporting its evolutionary ties to the gills.