How do the different visual receptors mediate vision? This
was one primary issue underlying my NSF-funded research as Assistant Professor
of Psychology at The Johns Hopkins University. These were the early days of a
powerful neurobiological approach dubbed "genetic dissection of the
nervous system." I was fortunate in my collaboration with Mr. W. A.
Harris, a graduate student at Caltech. We used mutants with vs. without
specific receptor types to systematically simplify the compound eye. We introduced
mutations of important genes: rdgA, rdgB, sev and ora which have been used in hundreds of
studies even to this day. I used electrophysiology to determine spectral
sensitivities of the 3 types of photoreceptor types in the compound eye: R1-6,
R7 and R8. We overturned the previously accepted dogma, introducing a new model
of receptor multiplicity which has been confirmed and elaborated upon since
that time. Most notably, we were the first to report that one receptor, R7, was
an ultraviolet (UV) receptor, a discovery which had evaded a decade and a half
of concerted earlier studies. My students and I also determined the properties
of the ocelli (small eyes between the compound eyes
on the fly's head). [Finding that Spatz’s lab in
Freiburg was also completing an overlapping study, we pooled our data with the
data of his student, Heinrich Reichert, for a joint paper, turning possible
competition into a friendly collaboration.] This receptor multiplicity has remained
of intense interest even to the present era as the differing rhodopsins which we originally characterized have been
cloned and studied with molecular techniques.
The plot of this story is the amazing good research breaks I had at the start of my assistant professorship.
At the end of the summer of 1973, I was at the XIII International Congress of Genetics where I presented work from my doctoral dissertation. Seymour Benzer was a big star, and I met him but only briefly. My session was toward the end of the meeting. I sat next to Jeff Hall, Benzer’s postdoc, the next best thing since I did not have a chance to talk with Benzer. Up walks Bill Harris, Benzer’s graduate student, who I did not know yet. Bill to Jeff “When are you leaving?” Jeff “Right after my talk. You?” “I wanna catch the talk after yours.” (Mine) I said “You don’t have to, I wrote the paper and brought a stack, here.” We met and he stayed. Jeff, being Benzer’s postdoc, had a well-attended talk, and there was such a mass exodus after his talk that I had trouble reaching the podium, so much that the moderator had to call my name again. Out of the blue when I was settled at Hopkins, Bill writes “Sorry I have not written. I have some interesting mutants. Would you be interested in doing ERGs on them and in collaborating?” Turns out that Benzer, unfolding his awesome second career in neurogenetics (after defining the gene in his first career) moved past his work with Hotta on vision and Bill, if he insisted on working on vision, would need to find a collaborator. I had my ERG apparatus constructed (with the help of machinist Bill Hamilton and electronics tech Tom Green, and the edict from departmental chair Bill Garvey that my set-up took precedence). Glen Pransky, an undergraduate premed, wrote a program (on punch cards) for the university’s computer and CalComp plotter. So we had things expedited at our end. And so, after starting my assistant professorship in 1973, in 1975, my paper, the first statement that R7 was a UV receptor, came out. Bill and I met for the second time Sunday night before the ARVO meeting where I gave him slides for his talk and he gave me some for mine and we practiced since my talk (on this topic) and his (on retinal degeneration) were bright and early the next morning. I sent copies of the paper and abstract to many researchers without solicitation, and so I won priority on important findings. Hans Joachem Autrum, the influential editor of Journal of Comparative Physiology (and heir to Nobelist von Frisch) must have thought me a rising star since he invited me to write the Die Natuurwissenschaften review (1976!) where I abstracted the contents of several paper to come, importantly that vitamin A deprivation preferentially decreases UV sensitivity, see link, and that flies are attracted to UV because of R7, see link. Bill was also instrumental in assembling a team of researchers, ourselves included, for a paper in the prestigious journal Nature (1977!), see link.
Selected publications on receptor spectral sensitivity:
Stark, W.S. Spectral selectivity of visual response alterations mediated by interconversions of native and intermediate photopigments in Drosophila. Journal of Comparative Physiology, 1975, 96, 343-356.
Stark, W.S., Ivanyshyn, A.M. and Hu, K.G. Spectral sensitivities and photopigments in adaptation of fly visual receptors. Die Naturwissenschaften, 1976, 63,513-518. (Invited review).
Harris, W.A., Stark, W.S. and Walker, J.A. Genetic dissection of the photoreceptor system in the compound eye of Drosophila melanogaster. Journal of Physiology, 1976, 256, 415-439.
Stark, W.S. Sensitivity and adaptation in R7, an ultraviolet photoreceptor, in the Drosophila retina. Journal of Comparative Physiology, 1977,115, 47-59.
Hu, K.G., Reichert, H. and Stark, W.S. Electrophysiological characterization of Drosophila ocelli. Journal of Comparative Physiology, 1978, 126,15-24.
Stark, W.S., Frayer, K.L. and Johnson, M.A. Photopigment and receptor properties in Drosophila compound eye and ocellar receptors. Biophysics of Structure and Mechanism, 1979, 5, 197-209. (Invited review to accompany European Neurosciences Association 1978 Meeting presentation).
Comparing with phototaxis analysis, there is an amazing correspondence of R1-6, R7 and R8 spectra determined by phototaxis and the ERG isolated by mutants or adaptation.
A diagram showing
R1-6, R7 and R8 photoreceptors, with their microvillar
rhabdomeres, in each ommatidium
of the compound eye
The first demonstration (from Stark, 1975) that R7 is a UV receptor, R8 is a blue-green receptor and R1-6 is a UV-blue receptor
A micrograph from Harris et al., 1976, the introduction of the sevenless (sev) mutant
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This page was last updated on July 15, 2014