Burr AHJ (1984) Worm Breeder's Gazette "modulation of reversal frequency by light and temperature changes."

Burr AHJ

[Worm Breeder's Gazette, 1984]

C. elegans can see! That is, its reversal frequency is increased by perpendicularly-incident light. Adult hermaphrodites were tested with 10 s periods of light stimulus, alternating with 20 s periods of dark. Reversals were counted during the 10 s of stimulus and the 10 s preceding the stimulus. Observation was by video camera and continuous near-infrared radiation. For 14 monochromatic stimuli ranging between 420 and 680 nm at a constant 3.4 x10+E13 photons s(-1) cm(-2), only those in the 520-600 nm range caused a significant increase in the frequency of reversals. Various possible radiant- heating effects, investigated in detail in a forthcoming paper (Burr, in press, Photochem. Photobiol.), are ruled out because the temperature changes would be too minute (less than 2x10+E-6 C, which is on the order of natural temperature fluctuations inside the nematode), and the wavelength dependence would be different. Moreover, a larger, 2x10+E-4 C change produced with a 1230 nm monochromatic stimulus had no significant effect on reversal probability. Therefore, the increase in reversal frequency must have been due to light. Much larger temperature changes did have an effect. Increasing or decreasing the temperature by 2 C from the acclimation temperature (20 C) increased average reversal frequency by 0.28 and 0.19 minute(-1), respectively. The responses adapted within 30 minutes. (Note: That the temperature changes affect reversal frequency differently from thermotaxis.) The sign of the latter response is different for increases and decreases of temperature (Hedgecock and Russell, Proc. Nat. Acad. Sci. USA 72, 4061-4065, 1975). The threshold light intensity was about 2x10+E13 photons s(-1) cm(-2) at 540 nm (40 lux or about 1/20 the illuminance of office lighting). At higher light intensities, reversal frequency reached a maximum level about 0.50 minute(-1) higher than the background frequency of spontaneous reversals (0.72 minute(-1)). The threshold intensity and maximum increment in frequency were not affected by increasing or decreasing the temperature by 2 C just prior to the experiment, in spite of the effect on background reversal frequency. Evidently the effects of light and temperature-change on reversal frequency are independent and additive. In another study, responses of C. elegans and Oncholaimus vesicarius were compared under identical conditions at 15 C and an intensity that was saturating for both. For O. vesicarius, background reversal frequency was slightly higher (0.93 vs 0.82 minute( -1)) and the increase due to perpendicularly-incident light was much greater (2.17 vs 0.68 minute(-1)). Oblique illumination of O. vesicarius elicited a strong negative phototaxis as found previously ( Burr, J. Comp. Physiol. 134, 85-93, 1979), whereas C. elegans had no directional tendency. This was as expected, since C. elegans lacks the pigment spots needed for detecting the direction of the light source (See Burr, Photomovement behavior in simple invertebrates, pp. 179-239 in: Photoreception and Vision in Invertebrates, M. A. Ali, ed., 1984).

Boom J et al. (1988) Worm Breeder's Gazette "cloning of putative opsin genes of C elegans."

Smith MJ, Boom J, Burr AHJ, Lobo K

[Worm Breeder's Gazette, 1988]

Because the 520-600 nm wavelength range of photosensitivity of C. elegans (Burr 1985, Photochem. Photobiol. 41, 577-582) is within the range expected for rhodopsin-like visual pigments, we investigated the possibility that the C. elegans genome contains an opsin gene. We used a 1.6 kb Drosophila ninaE opsin cDNA [cRh1], provided by Charles Zuker, to probe Southern blots of C. elegans genomic DNA digested with EcoRI. At a moderate stringency level (62 C; 1xSSPE) the probe identified 4 strongly and several weakly hybridizing bands ranging in size from 1.5 to 7.7 kb. Some opsin genes cross-hybridize at moderate to high stringencies (e.g. bovine rod-cell opsin cDNA [cRhB-rod] with vertebrate rod-cell opsin genes and cRh1 with the Drosophila Rh2 gene). Many require low stringencies (e.g. cRhB-rod with vertebrate cone- cell opsin genes and cRhB-rod with Drosophila opsin genes), while others do not cross-hybridize (e.g. cRh1 with the Drosophila UV- sensitive opsin genes Rh3 and Rh4). Though other signal proteins of the opsin family (adrenergic receptors and muscarinic acetylcholine receptors) have several structural and functional features in common with opsins, their genes do not cross-hybridize with opsin genes even within the same species (human) at low stringencies. In the light of these observations, our results at moderate stringency suggest that C. elegans has opsin gene(s) with relatively close resemblance to the ninaE gene of Drosophila. We have screened a C. elegans genomic library in Lambda Charon 4 phage (constructed by T. Snutch) with cRh1 under conditions identical to those used for the genomic blots. Thirteen positive phage giving strong hybridization signals at moderate stringency were grouped into 5 classes (designated s401-s405) based on the restriction fragment patterns produced by combined digestion with EcoRI and HindIII. Representative phage clones have been sent to Alan Coulson and John Sulston to be localized on the chromosomal contig map. The 5 classes were further characterized using probes produced by clevage of cRh1 with PstI. The 0.8 kb segment contains the major 3' portion of the coding region of the ninaE opsin (Zuker, et al. 1985, Cell 40, 851-858), including the sequences encoding the second extracellular loop and the 11-cis retinal binding site, both of which are highly conserved in opsins but not the other signal proteins. This probe hybridizes strongly with 7 different restriction fragments derived from s401-s405. The 0.6 kb PstI segment of cRh1 contains 5' noncoding sequences and the 5' third of the coding region, including the highly conserved first cytoplasmic loop, the putative binding site for G-protein in all of the signal proteins of the opsin family. It hybridizes weakly with the same fragments detected by the 0.8 kb probe and weakly with 2 unique fragments in s403. Thus, restriction and hybridization data suggest that our cloned DNA fragments may represent as many as 5 different opsin genes of C. elegans which may have greater sequence identity to the Rh1 (Drosophila ninaE) gene than that between Rh1 and some other opsin genes.