The optic lobe projection pattern of polarization-sensitive photoreceptor cells in Drosophila melanogaster

Histological staining of wild-type and sevenless transgenic Drosophila melanogaster bearing Rh3-lacZ fusion genes permits the selective visualization of polarization-sensitive R7 and R8 photoreceptor cells located along the dorsal anterior eye margin. Diffusion of beta-galactosidase throughout these cells reveals that they project long axons to the two most peripheral synaptic target rows of the dorsal posterior medulla, defining a specialized marginal zone of this optic lobe. Comparison of the staining patterns of marginal and nonmarginal Rh3-lacZ-expressing photoreceptor cells in the same histological preparations suggest that the marginal cells possess morphologically specialized axons and synaptic terminals. These findings are discussed with reference to the neuroanatomy of the corresponding dorsal marginal eye and optic lobe regions of the larger dipterans Musca and Calliphora, and in relation to the ability of Drosophila to orient to polarized light.