Carotenoid replacement in Drosophila: freeze-fracture electron microscopy

The tamas gene, identified as a mutation that disrupts larval behavior in Drosophila melanogaster, codes for the mitochondrial DNA polymerase catalytic subunit (DNApol-gamma125)

From a screen of pupal lethal lines of Drosophila melanogaster we identified a mutant strain that displayed a reproducible reduction in the larval response to light. Moreover, this mutant strain showed defects in the development of the adult visual system and failure to undergo behavioral changes characteristic of the wandering stage. The foraging third instar larvae remained in the food substrate for a prolonged period and died at or just before pupariation. Using a new assay for individual larval photobehavior we determined that the lack of response to light in these mutants was due to a primary deficit in locomotion. The mutation responsible for these phenotypes was mapped to the lethal complementation group l(2)34Dc, which we renamed tamas (translated from Sanskrit as "dark inertia"). Sequencing of mutant alleles demonstrated that tamas codes for the mitochondrial DNA polymerase catalytic subunit (DNApol-gamma125).

Control of Drosophila retinoid and fatty acid binding glycoprotein expression by retinoids and retinoic acid: northern, western and immunocytochemical analyses

In Drosophila, thorough retinoid deprivation is possible, optimizing investigation of the effects of vitamin A metabolites and retinoic acid on the visual system. Retinoids had been found to control transcription and translation of Drosophila's opsin gene. To follow this line of inquiry, we examined the effect of retinoids on the translation and transcription of a Drosophila Retinoid and Fatty Acid Binding Glycoprotein. Western blots showed that this protein is high in retinoid replete flies and low in deprived flies. Flies grown on media capable of activating the opsin gene's transcription and which contain alternate transcription activators including retinoic acid yielded extracts containing significant amounts of Retinoid and Fatty Acid Binding Glycoprotein. Immunocytochemistry confirmed its absence in deprived flies and its presence in flies reared or replaced on these diverse media containing retinoids or general nutrients. Immunocytochemistry localized Retinoid and Fatty Acid Binding Glycoprotein to the Semper (cone) cells and the intraommatidial matrix (the interphotoreceptor matrix of the ommatidium). Positive staining of Semper cells in mutants of the opsin gene and a mutant lacking receptors suggests that Retinoid and Fatty Acid Binding Glycoprotein does not depend on presence of opsin and that it is not synthesized in receptor cells respectively. Northern blots demonstrated greatly diminished mRNA for Retinoid and Fatty Acid Binding Glycoprotein in flies grown on deprivation food relative to flies grown on normal food. Although the synthesis of Retinoid and Fatty Acid Binding Glycoprotein does not require chromophore precursors as does that of opsin, the control of Retinoid and Fatty Acid Binding Glycoprotein and opsin transcription by retinoids including retinoic acid might very well be the same. Our results suggest that Retinoid and Fatty Acid Binding Glycoprotein may be involved in retinoid transport. Also, Semper cells may be analogous to vertebrate retinal pigment epithelium in retinoid metabolism and/or delivery.