Seminars and Events

Past Events

Category Seminar
Date and Time 2012-07-03 16:00 - 17:00
Venue Seminar Room A7F
Speaker Sachihiro Suzuki
Affiliation Department of Biological Structure, University of Washington, Seattle WA, USA
Title Symmetrical divisions dedicated to generating distinct cone photoreceptor types
Poster click here to download(PDF)
Host Masatoshi Takeichi
Summary In the vertebrate retina, color information is transmitted by cone photoreceptors with different spectral sensitivities. Although much is known about the transcriptional regulation underlying cone development and the timing of their generation relative to other retinal cell types during development, the location and nature of cell divisions that produce cones remained largely unknown. We thus chose zebrafish that has four distinct cone subtypes as our model animal and used in vivo multiphoton time-lapse microscopy to image the generation of cone. Time-lapse imaging of cells labeled using the thyroid hormone receptor β2 (trβ2) promoter revealed cone precursors dedicated to production of Long wavelength sensitive-cones (L-cones). The L-cone precursor underwent symmetric division at the apical surface without attaching the basal surface to give rise to a pair of L-cones. To examine the role of trβ2 in L-cone genesis, we knocked down trβ2 by morpholino oligonucleotide. Consistent with mouse trβ2 function, knockdown of trβ2 resulted in a loss of L-cone associated with a corresponding increase of UV light sensitive cones. Interestingly, almost all of the cones became L-cones when trβ2 was overexpressed around the time of precursor division. Furthermore trβ2 overexpression after cell division also caused L-opsin expression ectopically, but such late expression of trβ2 could not completely suppress expression of other opsins, giving rise to cones with expression of mixed cone opsins. Our findings suggest that trβ2 expression at around the precursor stage is sufficient to confer L-cone fate, preventing emergence of mixed cone types. Finally, we also observed symmetric divisions resulting in pairs of non-L cones, and divisions generating different cone types occur concurrently within an area. Thus, there exist dedicated precursors whose symmetric divisions produce each cone type. Our study demonstrates the first example of symmetrical divisions to generate a functionally distinct subtype in a single neuronal type.
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