Visual system development and function using molecular-genetic approaches
in Drosophila
Color vision is dependent upon the expression of
spectrally distinct visual pigments in different classes of photoreceptor cells.
This requires both a developmental program that generates different types of
photoreceptor cells, and a collection of unique visual pigments having different
spectral properties. My lab is working on aspects of both of these problems
using the fruit fly, Drosophila melanogaster, as an experimental
system.
Photoreceptor cell-fate determination and the
regulation of visual pigment gene expression:
The compound of eye of Drosophila is highly
patterned and has been used extensively as a model system in developmental
biology. We have found that the cell fate and visual pigment expression pattern
of adjacent photoreceptor cells is tightly coordinated. It appears that one
retinal cell type in each ommatidium (R7) adopts one of two different cell fates
in a stochastic manner, and then communicates this decision (inductively) to the
adjacent R8 cell. These events coordinate the expression of the visual pigments
in these two cells, and produce two types of optical units within the eye that
have distinct spectral sensitivities.
To examine this process at a genetic and molecular
level, we have identified a collection of mutants that have a variety of defects
in photoreceptor cell fate determination and visual pigment gene expression.
These mutants define genes that are required for the normal patterning of the
eye. One group of mutants shows defects in the stochastic determination event
within the R7 cell, and another group appears to have defects in the inductive
signal to the R8 cell. We are currently characterizing these mutations and
beginning the molecular analysis of the affected genes
Visual pigment studies:
We are also examining how the structures of different
visual pigments regulate their absorption spectra and photochemical properties.
We have identified specific amino acid residues that are responsible for
regulating UV vs. visible and blue vs. green absorption, and we are also
examining the spectral tuning of metarhodopsin, the activated form of the visual
pigment rhodopsin. In collaborative studies, we have examined the mechanism of
photoactivation and characterized the photo-intermediates of the
Drosophila rhodopsins using low temperature spectroscopic methods. We are
also studying the visual pigments of other invertebrate organisms.
Selected Publications
Britt, S.G., Feiler, R., Kirschfeld, K., and Zuker,
C.S. (1993) Spectral tuning of rhodopsin and metarhodopsin in vivo.
Neuron, 11, 29-39.
Chou, W.-H., Hall, K.J., Wilson, D.B., Wideman,
C.L., Townson, S.M., Chadwell, L.V., and Britt, S.G. (1996) Identification of a
novel Drosophila opsin reveals specific patterning of the R7 and R8
photoreceptor cells. Neuron, 17, 1101-1115.
Vinos,
J., Jalink, K., Hardy, R.W., Britt, S.G., Zuker, C.S. (1997) A G protein-coupled
receptor phosphatase required for rhodopsin function.Science,
277, 687-690.
Townson, S.M., Chang, B.S.W., Salcedo, E., Chadwell,
L.V., Pierce, N.E., and Britt, S.G. (1998) Honeybee blue- and
ultra-violet-sensitive opsins: Cloning, heterologous expression in Drosophila
and physiological characterization. J. Neurosci., 18,
2412-2422.
Chou, W.-H., Huber, A., Bentrop, J., Schulz, S., Schwab, K.,
Chadwell, L.V., Paulsen, R., and Britt, S.G. (1999) Patterning of the R7 and R8
photoreceptor cells of Drosophila: Evidence for induced and default cell-fate
specification. Development, 126, 607-616.
Salcedo, E.,
Huber, A., Henrich, S., Chadwell, L.V., Chou, W.-H., Paulsen, R., and Britt,
S.G. (1999) Blue- and green-absorbing visual pigments of Drosophila: Ectopic
expression and physiological characterization of the R8 photoreceptor
cell-specific Rh5 and Rh6 rhodopsins. J. Neurosci., 19,
10716-10726.
Vought, B.W., Salcedo, E., Chadwell, L.V., Britt, S.G.,
Birge, R.R., and Knox, B.E. (2000) Characterization of the primary
photointermediates of Drosophila rhodopsin . Biochemistry,
39, 14128-14137.
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