- 2011. UC Berkeley. Ph.D.
- Evolution and development of the insect visual system: from genes to behavior
We are interested in how insect visual systems can be modified for specific functions. For example, butterflies have more diverse retinal mosaics than Drosophila, allowing them to make additional color comparisons and to express a broader range of color-sensitive Rhodopsins. Butterflies deploy three types of ommatidia stochastically across their retina, compared to two in Drosophila. Papilionid butterflies (the swallowtails) use photoreceptors in one of these three ommatidial types to express a newly evolved red-sensitive Rhodopsin, expanding their range of color vision. We used CRISPR/Cas9, genome/transcriptome sequencing, and gene expression assays to understand the molecular basis for the production of three stochastic outcomes during development. Results show that butterflies have an additional, second R7-like photoreceptor in each ommatidium (“unit eye”) and that each makes an independent stochastic decision to express the transcription factor Spineless, yielding on/on, on/off, and off/off outcomes instead of just on/off found in Drosophila. Knocking out Spineless converts fate to a single ommatidial type. This work was featured on HBO/Vice (Season 4, Episode 1).
In contrast, another species of fly in the family Dolichopodidae (the “long-legged” flies) has non-stochastic, deterministically patterned retinas with alternating columns of ommatidial type. Photoreceptor morphology indicates that they have an improved ability to see through polarized light, which may help in catching prey on shiny leaf surfaces. We have sequenced the genome of a species in this group and raised antibodies against the Rhodopsins and homologs of the regulators of stochastic choices in flies. By examining both the underlying mechanisms and functional consequences of each type of patterning, as well as the changes involved in the evolutionary transition between them, we hope to better understand these fundamentally different types of cell fate specification.
Ongoing work is focused on understanding the genetic and developmental basis of the “Love Spot”, a male specific part of the visual system in various flies that is used for detecting and chasing females. Within this region, R7 photoreceptors that are normally used for color vision have been converted toward motion detection fate. They express a broad spectrum Rhodopsin and rewire their axons to the lamina, where motion processing first occurs. We are examining the role of specific transcription factors in this cell fate change, and hope to produce Love Spot-like R7 photoreceptors in Drosophila with the goal of understanding the control of cell fate and axon targeting in providing improved target detection and motion vision.
In each case examined, changes in cell fate specification help the animal meet the functional requirements of particular behaviors. In order to better understand cell fate specification at the level of single genes, we have begun to develop tools for live imaging of transcription in the retina using the MS2 system. This quantitative approach to measuring gene expression over time will build on my graduate work on mechanisms that make transcriptional outcomes robust and reliable. By also understanding control of cell fate specification at the level of transcription of single regulators we hope to understand the development and evolution of insect visual systems at levels ranging from individual genes to behavior.
- JSPS Post-Doctoral Fellowship - Temporary
- Revson Fellowship - Current