The physiology and ultrastructure of the antenna in Drosophila melanogaster have been examined in wild-type and lozenge mutants. Scanning electron microscopy (SEM) of sensilla on the antennal surface has revealed that in the wild-type the basiconic sensilla contain linear arrays of pores connected by longitudinal furrows and transected by shorter furrows. Sensilla trichodea also are shown to have pores, as revealed by examining transverse sections by transmission electron microscopy (TEM); these data directly address a longstanding controversy. Coeloconic sensilla, previously described as "pit sensilla" and as "grooved" sensilla, are shown to rise directly from the antennal surface, as opposed to lying below the antennal surface in pits; the previously observed grooves correspond to the junctions between bundled, finger-like projections. This description of coeloconic sensilla is supported by analysis of lz mutants, in which the projections of coeloconic sensilla splay apart. Coeloconic sensilla are also shown to undergo duplication on the lz3 antenna. Physiological recordings from the antenna show that responses to all odorants tested are severely decreased in lz mutants. Measurements made from different parts of the antenna show similar defects. Evidence is provided that both the physiological and ultrastructural defects map to the lz locus.
The ultrastructure and physiology of the maxillary palp of Drosophila melanogaster have been studied in wild-type and lozenge mutants. Olfactory physiology in the maxillary palp is shown to depend upon the lozenge(lz) gene. Reduced response amplitudes were recorded for all odorants tested, and the physiological defect was shown to map to the lz locus. The structure of the maxillary palp sensilla is described by scanning electron microscopy (SEM) at high magnification, initially in the wild-type. A linear arrangement of pores, connected by furrows, was found in one class of sensilla, the basiconic sensilla. In the lz3 mutant, morphological alterations in the basiconic sensilla and duplications of sensilla are documented by SEM. The correlation of structural abnormalities in the lz sensilla and physiological abnormalities in odorant response are consistent with an olfactory role for the basiconic sensilla of the maxillary palp.
A re-examination and modification of the very old oblique illumination technique has resulted in a method for contrast enhancement in microscopes, diffracted-light contrast (DLC), which provides high-contrast, high-resolution images of unstained biological material. The technique, which utilizes the diffracted light from the edge of a small, opaque plate, provides shadowcast images similar to those obtained by Nomarski DIC, anaxial illumination, modulation contrast, or single-sideband microscopy; however, it requires only a single additional component, which can be added to any bright field microscope. The contrast and three-dimensionality of the final image can be controlled by inserting differently shaped edges. Any bright field condenser will work with the technique and, consequently, it is a technique that may be especially useful with relatively basic, inexpensive laboratory and teaching microscopes although the image produced on a research grade microscope is of very high quality, comparable to that obtained with DIC.
By using experimental light regimes, it is possible to alter independently the timing of both multivesicular body (MVB) production and decreases in rhabdom diameter. As a result, two distinct phases of MVB synthesis are revealed, neither of which appears temporally linked to rhabdom shrinkage. This supports the idea that MVB production and diminishing rhabdoms are not causally related in the manner predicted by the lysosome-related-body (LRB) hypothesis of rhabdom cycling. Furthermore, a statistically significant relationship is found between midday rhabdom enlargement and a decrease in the fractional volume of MVBs.Since the initial observations of White ('67) and Eguchi and Waterman ('671, the turnover of photoreceptor membrane in arthropods has been examined with a variety of techniques. These studies have been largely concerned with those ultrastructural events initiated by lights-on, i.e., rhabdom shrinkage and multivesicular body (MVB) formation and degradation. In the crayfish eye, the photosensitive rhabdom is a relatively large (20-30 pm diameter) spindle-shaped structure. It is composed of microvilli that arise from the surface of eight surrounding retinular cells. At lights-on, the diameter of the rhabdom rapidly decreases and MVBs begin to accumulate in the cytoplasm of the retinular cells. Such observations gave rise to the hypothesis that the light-induced decrease in rhabdom diameter results from endocytosis of rhabdomeric microvilli. Microvilli are ingested as coated vesicles that then lose their coats and coalesce into MVBs. MVBs are enzymatically degraded into lamellar bodies (LB) and finally residual bodies (RB). Ferritin label (White, '68; White et al., '801, autoradiography (Hafner and Bok, '77) and acid phosphatase localizations (Eguchi and Waterman, '76; Blest et al., '80) have been used to strengthen this hypothesis. In addition, this lysosome-related-body (LRB) hypothesis is consistent with the long-held and well-substantiated belief that coated vesicles and MVB formation are a means of membrane uptake and degradation in other cell types (e.g., Farquhar and Palade, '60; Easton et al., '62; Ryser et al., '62; Friend and Farquhar, '67; Holtzman and Mercurio, '80).A recent experiment challenges the validity of the LRB mechanism as it pertains to the crayfish retina (Piekos, '87). In that study, it was demonstrated that the density of MVBs in the light-adapting crayfish retina is related to the density of vesiculating Golgi ALAN R. LISS, INC.bodies and not to the density of coated vesicles or the size of the rhabdom. It was hypothesized that MVBs may be comprised of newly synthesized vesicles that were applied to the rhabdom at midday.This experiment is designed to evaluate directly the effects of light on both rhabdom dimensions and MVB production and to test for possible midday relationships between those two organelles. MATERIALS AND METHODSCrayfish (Procambarus clarkii) were ordered from Carolina Biological Supply Co. in August 1987. The animals were kept for one week under an L...
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