John Harvard Distinguished Science Fellow
Gene duplication, co-option and the evolution of cephalopod visual system complexity
Abstract: The image forming eye is a classic model for the study of the evolution of biological complexity. The lens is a requisite innovation in all high-resolution, complex visual systems. The cephalopod has a highly acute visual system and is also a classic case of morphological convergence with the vertebrate eye. Both systems independently evolved a single-chambered eye with a cup shaped retina and a single refractive lens in the anterior. Almost nothing is known about the molecular-genetics of lens development in the cephalopod. The generation of new genetic material is considered a significant contributor to the evolution of biological novelty. We sought to understand if this mechanism may be contributing to cephalopod-specific visual system novelties. We identified a cephalopod-specific duplication of the transcription factor Sp6-9, with one paralog, DpSp6-9a, uniquely expressed in the lens-forming cells in the squid Doryteuthis pealeii. In addition, we find that DpSp6-9a is expressed during lens development in conjunction with a well-studied regulatory program canonically associated with proximal-distal patterning of animal appendages. To assess the homology of upstream regulation of these genes, we examined the role of Wnt signaling. We found that ectopically activating Wnt signaling leads to the loss of the lens and loss or decrease in limb-associated gene expression in the anterior segment. This work is a significant step forward in our understanding of the molecular basis of eye complexity in cephalopods, highlights the importance of transcription factor duplication, and sheds new light on the nature of phenotypes associated with co-opted canonical gene regulatory programs.
Host: Yun Zhang