***Cancelled*** "Conservation and divergence of retinal cell types during vertebrate evolution" Dr. Yohei Ogawa

******This seminar has been cancelled******

Due to unavoidable circumstances, we regretfully announce the cancellation of this seminar.

We apologize for any inconvenience and appreciate your understanding.

■Speaker■

Dr. Yohei Ogawa

Yohei Ogawa is a postdoc in the lab of Dr. Joseph C. Corbo at Washington University School of Medicine, USA. He received his Ph.D. for studies on transcription factors governing cone photoreceptor identity in zebrafish. He then expanded his interest to cell type diversity in vertebrate photoreceptor cells, and his present work focuses on comparative epigenomic analysis across vertebrate species. He often spends his holiday having a beer in local breweries in his town, Saint Louis.

■Abstract■

Conservation and divergence of retinal cell types during vertebrate evolution
Yohei Ogawa
Department of Pathology and Immunology, Washington University School of Medicine, USA

Cell type divergence and specialization during evolution are remarkable features in multicellular　organisms. Yet, it is challenging to define and compare cell types across the species. The fundamental　architecture of the vertebrate retina, consisting of three cellular layers and six major cell classes, has　remained largely invariant over half a billion years of evolution. On the other hand, individual　vertebrate　species have expanded or contracted the cell type repertoires within each retinal cell class to adapt to　specific light environments. The vertebrate retina can thus be a great model to address cell type divergence.
In this seminar, I will present our recent research progress about (I) cell-type divergence of zebrafish　photoreceptor cells by partitioning the phototransduction paralogs and (II) deep conservation of cis-regulatory codes in retinal cell classes.
(I) Divergence of zebrafish photoreceptor cells
Photoreceptors are the primary light-sensing cells of the vertebrate retina. They are categorized into　rods and cones, which specialized for dim- and bright-light vision, respectively. Zebrafish (Danio Rerio),　a teleost, retain all five photoreceptor subtypes inferred to have been present in the common ancestor of　jawed vertebrates. We used single-cell RNA-seq to profile photoreceptors in adult zebrafish. We found　subpopulations of green and red cones (previously shown to be located in the ventral retina) that express　red-shifted opsin paralogs as well as a unique combination of cone phototransduction genes (Ref. 1). The　expression of many paralogous phototransduction genes is partitioned among cone subtypes, analogous to the partitioning of the phototransduction paralogs between rods and cones seen across vertebrates. We also defined the expression pattern of transcriptional regulators in cone subtypes (Ref. 2 and 3), including many factors not previously implicated in photoreceptor development or differentiation. Partitioning of paralogous gene expression via the action of differentially expressed transcriptional regulators enables　diversification of cone subtypes in teleost.
(II) Deep conservation of cis-regulatory code in retinal cell class
We performed comparative epigenomic analysis using single-nucleus ATAC-seq (Assay for　Transposase-Accessible Chromatin using sequencing) with the retinas of three diverse vertebrate species　(zebrafish, chicken, and human). We focused on four cell classes (photoreceptors, bipolar cells, horizontal cells, and Müller glia) and all cell types within a single class (rods and cone subtypes). We identified cis-regulatory regions with cell-type-specific chromatin accessibility. Transcription factor binding site enrichments within cis-regulatory regions were deeply conserved at the level of cell classes. The deep conservation of cis-regulatory codes would reflect the architectural invariance of the vertebrate retina disconnected from the expansion and contraction of the retina cell types within individual vertebrate species.

References
1. Ogawa, Y. and Corbo, J. C. (2021). Partitioning of gene expression among zebrafish photoreceptor subtypes. Sci. Rep. 11, 17340.
2. Ogawa, Y., Shiraki, T., Asano, Y., Muto, A., Kawakami, K., Suzuki, Y., Kojima, D. and Fukada, Y. (2019). Six6 and Six7 coordinately regulate expression of middle-wavelength opsins in zebrafish. Proc. Natl. Acad. Sci. U. S. A. 116, 4651–4660.
3. Ogawa, Y., Shiraki, T., Fukada, Y. and Kojima, D. (2021). Foxq2 determines blue cone identity in zebrafish. Sci. Adv. 7, 2021.03.14.435350.