Interrelationships between Cellular Density,Mosaic Patterning,and Dendritic Coverage of VGluT3 Amacrine Cells

Amacrine cells of the retina are conspicuously variable in their morphologies, their population demographics, and their ensuing functions. Vesicular glutamate transporter 3 (VGluT3) amacrine cells are a recently characterized type of amacrine cell exhibiting local dendritic autonomy. The present analysis has examined three features of this VGluT3 population, including their density, local distribution, and dendritic spread, to discern the extent to which these are interrelated, using male and female mice. We first demonstrate that Bax-mediated cell death transforms the mosaic of VGluT3 cells from a random distribution into a regular mosaic. We subsequently examine the relationship between cell density and mosaic regularity across recombinant inbred strains of mice, finding that, although both traits vary across the strains, they exhibit minimal covariation. Other genetic determinants must therefore contribute independently to final cell number and to mosaic order. Using a conditional KO approach, we further demonstrate that Bax acts via the bipolar cell population, rather than cell-intrinsically, to control VGluT3 cell number. Finally, we consider the relationship between the dendritic arbors of single VGluT3 cells and the distribution of their homotypic neighbors. Dendritic field area was found to be independent of Voronoi domain area, while dendritic coverage of single cells was not conserved, simply increasing with the size of the dendritic field. Bax-KO retinas exhibited a threefold increase in dendritic coverage. Each cell, however, contributed less dendrites at each depth within the plexus, intermingling their processes with those of neighboring cells to approximate a constant volumetric density, yielding a uniformity in process coverage across the population.SIGNIFICANCE STATEMENT Different types of retinal neuron spread their processes across the surface of the retina to achieve a degree of dendritic coverage that is characteristic of each type. Many of these types achieve a constant coverage by varying their dendritic field area inversely with the local density of like-type neighbors. Here we report a population of retinal amacrine cells that do not develop dendritic arbors in relation to the spatial positioning of such homotypic neighbors; rather, this cell type modulates the extent of its dendritic branching when faced with a variable number of overlapping dendritic fields to approximate a uniformity in dendritic density across the retina.     

Differential distribution of pepsinogen II between the zones of the human prostate and the seminal vesicle

Pepsinogen II (PG II) is a gastric proenzyme which has previously been found in both human seminal fluid and the prostate gland. However, no regional distribution of PG II has been noted within the prostate nor has it been found in the seminal vesicle. Bouins-fixed sections of central zone, peripheral zone and seminal vesicle, taken from 10 prostates removed at radical prostatectomy or cystectomy, were exposed to antibody against PG II and stained using the A-B-C immunoperoxidase technique. Formalin-fixed tissue from autopsy prostates of four men in the third decade, and six cases with BPH nodules, were also examined for PG II activity. In nine of 10 seminal vesicles, and seven of 10 central zone samples, more than 50 per cent of the cells stained positive for PG II. By contrast, in nine of 10 peripheral zone samples staining was present in five per cent or less of the epithelial cells. Similarly, PG II activity in the four autopsy prostates occurred almost entirely within the central zone and ended abruptly at the boundary between the peripheral and central zones. BPH nodules contained no PG II activity. These findings provide the first evidence that the central and peripheral zones may serve different biological functions. Embryologically it is currently thought that the prostate is of endodermal origin and the seminal vesicle of mesodermal origin. The presence of large amounts of PG II in both the seminal vesicle and central zone lends support to the hypothesis of a common mesodermal origin for these two structures.     

Antigenic and virulence properties of Pasteurella haemolytica leukotoxin mutants.

Antigenic properties of two mutants of Pasteurella haemolytica, strains 59B0071 and 59B0072, that do not produce detectable leukotoxin were investigated. Western blot (immunoblot) analysis with a number of polyclonal sera from animals recovering from pasteurellosis revealed that both mutants secreted a variety of antigens that were also present in cultures of several wild-type strains. These antigens ranged from about 100 to 15 kDa. Mutant strain 59B0071 was found to be totally deficient in leukotoxin, as judged not only by Western blotting but also by cytotoxicity assays with bovine lymphoma (BL-3) cells or bovine polymorphonuclear cells as targets. The mutant strain 59B0071 had normal levels of a secreted sialylglycoprotease, however. When strains were tested for virulence in goat and cattle challenge experiments, a reduction in mortality and lung lesions was observed with the mutant 59B0071 in comparison with results obtained with wild-type strains. These results are consistent with an important role for leukotoxin in P. haemolytica virulence and suggest that leukotoxin-negative mutants may be useful tools in the investigation of other virulence properties involved in P. haemolytica infections.     

Marchiafava-Bignami Disease

Marchiafava-Bignami disease is a rare demyelinating disease involving the corpus callosum and other central white matter tracts. In the patient described here, the disease produced extensive demyelination of the corpus callosum and deep cerebral white matter. This widespread demyelination, confirmed pathologically, was associated with a fulminant fatal course. The magnetic resonance imaging appearance is quite suggestive of Marchiafava-Bignami disease and plays an important role in the premortem diagnosis.     

Compartmentalization of anterogradely and retrogradely transported organelles in axons and growth cones from chick optic tectum

Previous work suggests that organelles contacting microtubules in axons are in fast transport. Here, we examine the distribution of organelles contacting microtubules in growing axons and growth cones from chick optic tectum. Five axon segments, each 10 microns long, and 4 entire growth cones were reconstructed from serial electron micrographs of quick-frozen, freeze-substituted chick optic tectum. Organelles contacting microtubules in axons are evenly distributed along all microtubules. Smaller organelles, presumably in anterograde transport, are enclosed in fascicles of microtubules, while larger organelles in retrograde transport lie outside the fascicles. In contrast, organelles contacting microtubules are prevalent only in the most proximal parts of the growth cone, before the microtubule fascicles splay out more distally. The distance between noncontacting organelles and microtubules also becomes progressively greater, reaching a maximum in the mid- and more distal region of the growth cone. Contacts with microtubules of both the smaller, presumably anterogradely transported organelles, as well as the larger, presumably retrogradely transported organelles, abruptly become less frequent in the proximal midregion of the growth cone. It is therefore of possible significance in stopping and starting microtubule-based organelle transport that microtubules change from a straight to an undulating configuration in the midregion of the growth cone. The decrease in organelle binding to microtubules at the demarcations between the straight and undulating microtubule segments may depend on proteins or other local factors as well as the splaying out of the microtubule bundles.