Phospholipid methyltransferase activity in pancreatic islets: activation by calcium

Pancreatic islet homogenates contain a Mg2+-requiring phospholipid methyltransferase activity, the activity of which was doubled by calcium (K0.5 less than 5 microM). Other divalent metal ions stimulated the activity from 11 to 35%, but zinc and strontium were inhibitory. Cyclic AMP had no effect on the enzyme activity and cyclic GMP inhibited it slightly. Calcium increased the Vmax of the enzyme without affecting its Km with respect to S-adenosylmethionine (6 microM). Chlorpromazine, trifluoperazine, and dibucaine inhibited the calcium-stimulatable activity without affecting the activity in the absence of calcium. Phosphatidylserine stimulated, and arachidonic acid and palmitic acid inhibited, the basal enzyme activity. The methylated products were found to be primarily mono- and dimethylphosphatidylethanolamine (30%) and phosphatidylcholine (43%) and an, as yet unidentified, nonpolar lipid fraction (27%), as judged by thin-layer chromatography. In the presence of calcium, incorporation of methyl groups into phosphatidylcholine, mono- and dimethylphosphatidylethanolamine, and nonpolar lipids was increased by 131, 60, and 46%, respectively. Based on the localization of the enzyme activity in the insulin secretory granule fraction, it is proposed that phospholipid methylation plays a role in coupling the stimulus to the initial events in insulin secretion, leading to the exocytosis of insulin.     

Phylogenetic distribution in the genus Mus of t-complex-specific DNA and protein markers: inferences on the origin of t-haplotypes

We have examined the phylogenetic distribution of two t-specific markers among representatives of various taxa belonging to the genus Mus. The centromeric TCP-1a marker (a testicular protein variant specific for all t-haplotypes so far studied) has also been apparently detected in several non-t representatives of the Mus IVA, Mus IVB, and probably M. cervicolor species. By contrast, a t-specific restriction- fragment-length polymorphism allele (RFLP) of the telomeric alpha- globin pseudogene DNA marker alpha-psi-4 was found only in animals belonging to the M. musculus-complex species either bearing genuine t- haplotypes or, like the M. m. bactrianus specimen studied here, likely to do so. This t-specific alpha-psi-4 RFLP allele was found to be as divergent from the RFLP alleles of the latter, non-t, taxonomical groups as it is from Mus 4A, Mus 4B, or M. spretus ones. These results suggest the presence of t-haplotypes and of t-specific markers in populations other than those belonging to the M. m. domesticus and M. m. musculus subspecies, implying a possible origin for t-haplotypes prior to the radiation of the most recent offshoot of the Mus genus (i.e., the spretus/domesticus divergence), some 1-3 Myr ago.      

Cell kinetics of vocal fold epithelium in rats.

In order to investigate the kinetics of vocal fold epithelium a bromodeoxyuridine-anti bromodeoxyuridine method has been applied in vivo at both light and electron microscopy level. This method is able to define the length of both epithelium turnover and cell-cycle in basal elements, as well as the existence of a higher proliferation rate during night time in comparison with day time. Moreover distinct labeling patterns observed in incorporating cells allow us to define the precise localization in S-phase of cycling elements.     

A study of photoreceptor-retinal pigment epithelium complex: age-related changes in monkeys

Retinas of 4-, 10-, and 20-year-old monkeys were studied by light microscopy, electron microscopy, and scanning electron microscopy. Sections from the midperipheral region of every retina were selected for comparison. Although no significant differences were found between 4- and 10-year-old retinas, four major changes were found in 20-year-old monkey retinas: (i) increased number of displaced photoreceptor cells (DPC), (ii) increased number of macrophages of different morphology in subretinal space, (iii) increase in pigment granules in retinal pigment epithelium (RPE) cells, and (iv) altered morphology of Muller cells. DPC included both rods and cones. Their location and morphology depended on the stage of their displacement. These cells were usually oval or rounded in shape and were found either among the outer segments of other photoreceptor cells, having stalks extending into the outer nuclear layer, or were located in the subretinal space and had no stalk. A narrow space around the DPC stalks, indicating a change in the intercellular connection between photoreceptor cells and Muller cells, was observed. Furthermore, the Muller cells related to DPC had shortened and markedly reduced microvilli. Two types of macrophages were found in the subretinal space of aged monkey retinas. One type was similar in morphology to RPE cells. Some of these cells were noticed detaching from RPE. Other types of macrophages were nonpigmented. The modifications in RPE were closely related to the changes in the associated neuroretina. The RPE cells in aged retina were devoid of microvilli or had a few thin microvilli. The pleomorphic pigment granules were dispersed throughout the cytoplasm. These cells varied in their size, shape, and surface features. These changes could significantly alter the retinal metabolic equilibrium and may be indicative of age related degenerative processes.     

A quantitative cytochemical study of determination for xylem-element formation in response to wounding in roots of Pisum sativum L.

Quantitative cytochemical studies of cortical parenchyma cells of roots of Pisum sativum in which the central vascular bundle is severed, showed esterase activity to be an early marker of the determination of cells to form a vascular bridge. Explantation, onto a basal culture medium, of wound segments taken from roots at different times after severing the stele showed the irreversibility of the esterase activity on removal from the inducing environment, so confirming this as a marker of cell determination. A general determination for the stele was shown to occur by 8–10 h after wounding, but information relating to tracheid secondary-cell-wall formation was not apparently available until 18–20 h after wounding. Determination appeared to occur well before mitosis. The timings of the differentiation steps indicate a simple diffusion model to explain the mechanism of arrival of the initiating molecules.     

A quantitative cytochemical method for phosphofructokinase in plant tissues

A quantitative cytochemical method for the demonstration of phosphofructokinase has been successfully applied to a range of plant tissues. The findings indicate that this enzyme system may be assayed as an indicator of glycolytic activity in plant cells, and furthermore tha the very high endogenous phosphoenolpyruvate concentrations may not be rate limiting in vivo.     

Improved bromodeoxyuridine/DNA analysis by anti-BudR monoclonal antibody versus right angle light scatter

Summary Dynamic cell cycle analysis is based on the incorporation of labelled precursors into DNA. Although antibodies to BrdU are very useful for analysing in flow cells which synthesize DNA, this approach has two main limitations. First, the detection of low incorporating cells is often difficult; second, four parameter flow cytometry is not able to correlate cell cycle to any other cellular marker. We have developed a methodology that, employing an IgG_H+L as a second antibody and side scatter instead of propidium iodide fluorescence, allows a better discrimination of BudR⁺ cells. This approach allows the collection of an extra-fluorescent signal, and the analysis of specific cellular markers within the cell cycle.