B.S. 1975, Western Michigan University; Ph.D., 1983 U.C. Santa Barbara; Postdoctoral Fellowship, 1983-86, U.C. Los Angeles;
Postdoctoral Fellowship, 1986-89, U.C. San Diego.

The Molecular Genetics of Protein Trafficking and Targeting in Drosophila

We are taking a genomics approach to identify novel loci involved in photoreceptor cell function in Drosophila melanogaster. One area of emphasis is dissecting the molecular basis of signaling in protein trafficking and targeting. We are specifically focused on the mechanisms that underlie rhodopsin transport through the secretory pathway in the photoreceptor cells. The major rhodopsin in Drosophila is called Rh1 and it displays 22% amino acid identity with human rhodopsin. In both humans and flies, during biosynthesis, rhodopsin, as well as the other components of phototransduction are transported through the secretory pathway, to their final destination for vision. We have previously shown that several mutations in Rh1 result in defects in its transport through the secretory pathway leading to retinal degeneration. In fact, four mutations that we identified in Drosophila correspond to identical mutations that have been implicated in an inherited human retinal degeneration disorder called retinitis pigmentosa (RP). Studies that we are conducting in flies are providing insights for mechanisms of retinal degeneration in human retinal degeneration disease.

A cross section of the photoreceptors in the Drospohila compound eye reveals that the rhabdomeres of the R1-6 photoreceptors are immunolabeled with an antibody directed to Rhodopsin (green). The nuclei are shown in blue (ToPro). In addition, the InsP3 receptor immunolocalizes to the endoplasmic reticulum in a perinuclear fashion as well as in a punctate pattern consistant with vesicular labeling (Texas red). Deletion of the only InsP3 receptor gene in the Drosophila genome eliminates the InsP3 receptor immunoreactivity and results in retinal degeneration, but phototransduction is unaffected.

The other area of focus in the lab is on the role of calcium in phototransduction. We are utilizing a combined molecular, genetic, biochemical, electrophysiological, and cell biological approach to characterize a novel sodium/calcium-potassium exchanger (NCKX) expressed in the Drosophila photoreceptor cells. Exchangers play a crucial role in modulating intracellular calcium and in human and Drosophila photoreceptor cells.

Nckx30C and Calx are expressed in the adult eye and brain of Drosophila.
(A) Shown are in situ hybridization to 14um cryostat sections of adult heads hybridized with digoxigenin-labeled riboprobes. (A) antisense riboprobe for Nckx30C (B) sense probe for Nckx30C (C) antisence riboprobe for Calx (D) sense riboprobe for Calx. (L) lamina, (M) medulla and (Br) the brain.

Rosenbaum, E. E., R. C. Hardie and N. J. Colley (2006) Calnexin is essential for rhodopsin maturation, Ca²⁺ regulation and photoreceptor cell survival. Neuron. 49:229-241.

LaLonde, M. M., H. Janssens, N. J. Colley, W. Stark and M. A. Frohman (2005) Regulation of phototransduction responsiveness and retinal degeneration by a phospholipase D-generated signaling lipid. J. Cell Biol. 169:471-479.

Cohen, J. H., J. Piatigorsky, L. Ding, N. J. Colley, R. Ward and J. Horwitz (2005) Vertebrate-like βγ-crystallins in the ocular lenses of a copepod. Journal of Comparative Physiology A. 191 (3):291-298.

Winkfein, R. J., B. Pearson, R. Ward, R. Szerencsei, N. J. Colley and P. P. M. Schnetkamp (2004) Molecular characterization, functional expression and tissue distribution of a second NCKX Na⁺/Ca²⁺-K⁺ exchanger from Drosophila. Cell Calcium, 36 (2):147-155.

Webel, R., K. Haug-Collet, B. Pearson, R. T. Szerencsei, R. J. Winkfein, P. P. M. Schnetkamp and N. J. Colley (2002) Potassium-dependent sodium-calcium exchange through the eye of the fly. Ann N Y Acad Sci., 976:300-314.

Mollereau, B., M. Dominguez, R. Webel, N. J. Colley, B. Keung, J. F. de Celis and C. Desplan (2001) Two-step process for photoreceptor formation in Drosophila. Nature, 412 (6850):911-913.

Hartman, S. J., I. Menon, K. Haug-Collet and N. J. Colley (2001) Expression of Rhodopsin and arrestin during the light-dark cycle in Drosophila. Molecular Vision, 7:95-100.

Colley, N. J. (2000) Actin' up with Rac1. Science, 290 (5498):1902-1903.

Raghu, P., N. J. Colley, R. Webel, T. James, G. Hasan, M. Danin, Z. Selinger and R. C. Hardie (2000) Normal phototransduction in Drosophila photoreceptors lacking an InsP₃ receptor gene. Mol. Cell Neurosci., 15:429-445.

Webel, R., I. Menon, J. O'Tousa and N. J. Colley (2000) Role of asparagine-linked oligosaccarides in Rhodopsin maturation and association with its molecular chaperone, NinaA. J. Biol. Chem., 275 (32): 24752-24759.

Haug-Collet, K., B. Pearson, R. Webel, R. T. Szerencsei, R. J. Winkfein, P. P. M. Schnetkamp and N. J. Colley (1999) Cloning and characterization of a potassium-dependent sodium/calcium exchanger in Drosophila. J. Cell Biol., 147 (3):659-669.

Sturtevant, M. A., M. Roark, J. W. O'Neill, B. Biehs, N. J. Colley and E. Bier (1996) The Drosophila rhomboid protein is concentrated in patches at the apical cell surface. Dev. Biol., 174 (2):298-309.

Colley, N. J., J. A. Cassill, E. K. Baker and C. S. Zuker (1995) Defective intracellular transport is the molecular basis of Rhodopsin-dependent dominant retinal degeneration. Proc. Natl. Acad. Sci. USA, 92 (7):3070-3074.

Wu, L., B. Niemeyer, N. J. Colley, M. Socolich and C. S. Zuker (1995) Regulation of PLC-mediated signalling in vivo by CDP-diacylglycerol synthase. Nature, 373:216-222.

Yarfitz, S. L., J. L. Running Deer, G. Froelick, N. J. Colley and J. B. Hurley (1994) In situ assay of light-stimulated G protein activity in Drosophila photoreceptor G protein β mutants. J. Biol. Chem., 269 (48): 30340-30344.

Baker, E. K., N. J. Colley and C. S. Zuker (1994) The cyclophilin homolog NinaA functions as a chaperone, forming a stable complex in vivo with its protein target Rhodopsin. EMBO J., 13 (20):4886-4895.

Dolph, P. J., H. Man-Son-Hing, S. Yarfitz, N. J. Colley, J. L. Running Deer, M. Spencer, J. B. Hurley and C. S. Zuker (1994) An eye-specific Gβ subunit is essential for termination of the phototransduction cascade. Nature, 370 (6484):59-61.

Dolph, P. J., R. Ranganathan, N. J. Colley, R. W.Hardy, M. Socolich and C. S. Zuker (1993) Arrestin function in inactivation of G protein-coupled receptor Rhodopsin in vivo. Science, 260 (5116):1910-1916.

Colley, N. J., E. K. Baker, M. A. Stamnes and C. S. Zuker (1991) The cyclophilin homolog NinaA is required in the secretory pathway. Cell, 67 (2): 255-263.

Colley, N. J., K. T. Tokuyasu and S. J. Singer (1990) The early expression of myofibrillar proteins in round postmitotic myoblasts of embryonic skeletal muscle. J. Cell Sci., 95:11-22.

Williams, D. S., N. J. Colley and D. B. Farber (1987) Photoreceptor degeneration in a pure-cone retina: Effects of cyclic nucleotides, and inhibitors of phosphodiesterase and protein synthesis. Invest. Ophthalmol. Vis. Sci., 28 (7):1059-1069.

Colley, N. J., V. M. Clark and M. O. Hall (1987) Surface modification of retinal pigment epithelial cells: Effects on phagocytosis and glycoprotein composition. Exp. Eye Res., 44 (3):377-392.

Williams, D. S., N. J. Colley, D. H. Anderson, D. B. Farber and S. K. Fisher (1986) In vitro maintenance of a pure-cone retina. Invest. Ophthalmol. Vis. Sci., 27 (5):666-673.

Colley, N. J. and M. O. Hall (1986) Phagocytosis of light- and dark-adapted rod outer segments by cultured RPE cells: A reassessment. Exp. Eye Res., 42 (4):323-329.

Colley, N. J. and R. K. Trench (1985) Cellular events in the reestablishment of a symbiosis between a marine dinoflagellate and a coelenterate. Cell Tissue Res., 239:93-103.

Colley, N. J. and R. K. Trench (1983) Selectivity in phagocytosis and persistence of symbiotic algae in the scyphistoma stage of the jellyfish Cassiopeia xamachana. Proc. R. Soc. Lond., 219:61-82.

Trench, R. K., N. J. Colley, and W. K. Fitt (1981) Recognition phenomena in symbioses between marine invertebrates and "zooxanthellae": Uptake, sequestration and persistence. Ber. Duets. Bot. Ges. Bd., 94:529-545.