PhD Proposal Seminar – Emily Dong (Chang and Tropepe Lab)

Examining the role of rod development genes in the evolution of transmuted photoreceptors in squamates

Abstract

The evolution of a duplex of highly specialized photoreceptors (rods and cones) in vertebrates has allowed for their invasion into a diversity of environmental niches. Among vertebrates, squamates (a group including snakes and lizards) are unique in having evolved simplex retinas by the repeated secondary losses of either rods or cones as an adaptation to new light environments. The loss of duplexity in squamates appears to have occurred not by the outright loss of one type, but by “transmutation” or the evolutionary transition between rods and cones, whereby one photoreceptor class evolves features of the other.

Transmuted photoreceptors have been identified by molecular and morphological means in adult eyes. However, it remains unclear how these photoreceptors arise during embryonic development, leaving conserved rod vertebrate photoreceptor development genes including NRL, NR2E3, and CRX unexplored in squamates. I hypothesize that this rod-determining developmental network has been a target for selection in squamate lineages, causing adaptive changes in their functional capacity to induce rod identity, leading to transmutation.

To address this, my first Aim is a computational analysis of evolutionary selection pressures on orthologous squamate sequences. My second Aim is focused on the temporal and spatial expression patterns of these same genes in gecko embryos. Lastly, my third aim tests hypotheses developed from the molecular evolution analyses in Aim 1 by expressing squamate proteins in cultured mammalian cells and in the developing zebrafish retina. My research proposal touches on evolutionary, developmental, and functional perspectives that can be united for a holistic view of vertebrate photoreceptor identity, with a particular focus on how squamate groups have evolved photoreceptors that largely lie outside the typical photoreceptor duplex.

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Join Zoom Meeting

https://us02web.zoom.us/j/86156218181?pwd=YUcxMVN6dUxRY1FWaHpQSENFUGlhUT09

Meeting ID: 861 5621 8181

Host: Belinda Chang (belinda.chang@utoronto.ca)

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