Intracellular calcium redistribution during mating in Chlamydomonas reinhardii

Gametes of the unicellular green alga Chlamydomonas reinhardii recognize and adhere to cells of the opposite mating type by flagellar contact. Adhesion between these specialized organelles signals a rapid series of mating events which result in gamete fusion. The sequence of morphological changes (flagellar tip activation, cell wall loss, and mating structure elongation), which occur as a consequence of the sexual signalling, have been characterized. The signalling mechanisms have, however, not been defined. Calcium is known to be involved during fertilization of animal species. Increased intracellular free calcium, which can be achieved either by calcium influx or by mobilization of ions from intracellular stores, has been observed during activation of both eggs and sperm. A recent report by Bloodgood & Levin that gametes of C. reinhardii preloaded with 45Ca showed a transient increase in Ca efflux following mating, suggests that intracellular Ca redistribution may also accompany mating in this algal species. We have used X-ray microanalysis to analyze the subcellular distribution of bound calcium during mating in Chlamydomonas reinhardii. X-ray maps reveal that calcium is sequestered in discrete granules within the gamete cell body prior to mating and that during activation and cell fusion, calcium is diffuse throughout the cell. This suggests the possibility that calcium serves as a second messenger in this species.     

The strength of SMAD1/5 activity determines the mode of stem cell division in the developing spinal cord

The different modes of stem cell division are tightly regulated to balance growth and differentiation during organ development and homeostasis. However, the mechanisms controlling such events are not fully understood. We have developed markers that provide the single cell resolution necessary to identify the three modes of division occurring in a developing nervous system: self-expanding, self-renewing, and self-consuming. Characterizing these three modes of division during interneuron generation in the developing chick spinal cord, we demonstrated that they correlate to different levels of activity of the canonical bone morphogenetic protein effectors SMAD1/5. Functional in vivo experiments showed that the premature neuronal differentiation and changes in cell cycle parameters caused by SMAD1/5 inhibition were preceded by a reduction of self-expanding divisions in favor of self-consuming divisions. Conversely, SMAD1/5 gain of function promoted self-expanding divisions. Together, these results lead us to propose that the strength of SMAD1/5 activity dictates the mode of stem cell division during spinal interneuron generation.     

Beta-adrenergic receptor-linked adenylate cyclase in rat posterior pituitary

A specific β-adrenergic-stimulated cyclic AMP generating system has been evidenced in rat posterior pituitary. This is clearly demonstrated by: 1) the adenylate cyclase (AC) affinity for stimulants was in the order ISO > NA > DA, and 2) propranolol, a specific β-adrenergic receptor blocker, was the only antagonist of the system. Clonidine and apomorphine were completely inactive, thus excluding an α-adrenergic and/or dopaminergic component in this AC system. Our data also indicate that dopaminergic receptors present in both pituitary lobes are not coupled to an AC.     

Human intestinal parasites in Subsaharan Africa. III. Pemba Island (Zanzibar-Tanzania)

The authors carried out a coprological survey in Pemba Island, analysing, by modified Ritchie technique, 413 stools samples. The specimens were collected among the population from apparently healthy subjects chosen at random in a number equal to 2% of the whole population. The examined subjects were divided in 3 age groups, 211 were males, 202 females. The following results were obtained (in order of prevalence): a) Protozoa: Entamoeba coli 35.6%, Giardia intestinalis 5.6%, Endolimax nana 4.3%, E. histolytica 3.1%, Chilomastix mesnili 2.9%, Iodamoeba buetschlii 4.3%, E. hartmanni 0.7%; b) Helminths: Trichuris trichiura 87.9%, Ancylostomatidae 67.5%, Ascaris lumbricoides 39.7%, Strongyloides stercoralis 18.9%, Schistosoma haematobium 1.9%, S. mansoni 0.2%, S. fuelleborni 0.2%, Enterobius vermicularis 0.2%. The high moisture of soil and the rain distribution during the year could be favouring the high prevalence of T. trichiura and Ancylostomatidae. The case of schistosomiasis due to S. mansoni reported, seems to be imported from the Mainland, while the case of S. fuelleborni could be autochtonous. Totally, 392 subjects (94.4%) were found positive for pathogenic species (Helminths and Protozoa).     

Restriction fragment length polymorphism at the HLA-C locus

We have used the HLA-C-specific DNA probe pC250 to investigate restriction fragment length polymorphism (RFLP) at the HLA-C locus. Genomic Southern blot hybridization included DNA prepared from a panel of homozygous typing cells representing serological specificities Cw1 to Cw8 and also from samples representing Cw blanks. Although many restriction nucleases failed to reveal any polymorphism, RFLPs were evident with Taq I, Pvu II, Bst XI, Nde 1, and Nci I in addition to the previously reported Eco RI. In the case of Bst XI, a unique RFLP defined a subset of serologically defined Cw blanks. Comparison of RFLP sizes with restriction fragment lengths obtained from the known HLA-Cw3 gene sequence permitted the localization of intragenic C locus RFLLs and the identification of a variable Taq I site in the second intron, a variable Nci I site near the end of the fourth exon, and a variable Pvu lI site in the fifth intron.     

Reaction of T lymphocytes with anti-T3 induces translocation of C-kinase activity to the membrane and specific substrate phosphorylation

Reaction of the T cell membrane with monoclonal antibodies to T3 can initiate cellular activation, and this is associated with increased intracellular Ca2+ and inositol-trisphosphate (IP3) release. We therefore studied the possible involvement of Ca2+/phospholipid-dependent kinase (C-kinase) in these phenomena. Quantitative assays of exogenous substrate phosphorylation in unstimulated cells showed Ca2+/phospholipid-dependent kinase activity in the cytosol, but no comparable activity in the particulate fractions corresponding to membrane and cytoskeleton material. At concentrations of soluble anti-T3 that partially activate T cells in the absence of macrophages, there was a 50 to 60% decrease in C-kinase activity in the cytosol, with a comparable increase in activity in the membrane fraction. A similar transfer of activity was also induced with the known C-kinase activator, 12-O-tetradecanoyl-phorbol-13-acetate, although redistribution was more rapid in onset, more complete, and more sustained. Redistribution of enzyme activity was additionally confirmed by qualitative assays of endogenous substrate phosphorylation. Labeling of intact cells followed by immunoprecipitation analysis with anti-T3 indicated signal-dependent phosphorylation of two components of the T3 complex and an unidentified 94,000 substrate that was resistant to reduction and alkylation. These findings are consistent with an important role for C-kinase in transduction of membrane events by the T3-Ti complex.