Orexin A/Hypocretin Modulates Leptin Receptor-Mediated Signaling by Allosteric Modulations Mediated by the Ghrelin GHS-R1A Receptor in Hypothalamic Neurons

The hypothalamus is a key integrator of nutrient-seeking signals in the form of hormones and metabolites originated in both the central nervous system and the periphery. The main autocrine and paracrine target of orexinergic-related hormones such as leptin, orexin/hypocretin, and ghrelin are neuropeptide Y neurons located in the arcuate nucleus of the hypothalamus. The aim of this study was to investigate the expression and the molecular and functional relationships between leptin, orexin/hypocretin and ghrelin receptors. Biophysical studies in a heterologous system showed physical interactions between them, with potential formation of heterotrimeric complexes. Functional assays showed robust allosteric interactions particularly different when the three receptors are expressed together. Further biochemical and pharmacological assays provided evidence of heterotrimer functional expression in primary cultures of hypothalamic neurons. These findings constitute evidence of close relationships in the action of the three hormones already starting at the receptor level in hypothalamic cells.     

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.     

Reproductive capacity,germination and survivorship of Lithospermum caroliniense on Lake Huron sand dunes

Summary The flowering of pin (long-styled) and thrum (short-styled) plants in populations of Lithospermum caroliniense (Walt.) McMill. was synchronized and both morphs had an extended period of flowering. The plants produced a large number of flowers that did not set seeds — hence the seed production per plant was very low. The seeds showed strong dormancy. Even under natural conditions, only 19% of the seeds produced seedlings. However, seedling survival was relatively high probably due to rapid root growth to deeper layers where moisture was not limiting. The probability of survival of seedlings increased with age; survival of seedlings, juveniles and adults after 2 years was 39, 68 and 98%, respectively. The dry weight of roots increased from 10% in June to 42% in September whereas the proportion of biomass contained in leaves, stems and hypocotyls decreased with age.     

A strictly anaerobic betaproteobacterium Georgfuchsia toluolica gen. nov., sp. nov. degrades aromatic compounds with Fe(III), Mn(IV) or nitrate as an electron acceptor

A bacterium (strain G5G6) that grows anaerobically with toluene was isolated from a polluted aquifer (Banisveld, the Netherlands). The bacterium uses Fe(III), Mn(IV) and nitrate as terminal electron acceptors for growth on aromatic compounds. The bacterium does not grow on sugars, lactate or acetate. Phylogenetic analysis of the 16S rRNA gene sequence indicated that strain G5G6 belonged to the Betaproteobacteria . Its closest, but only distantly related, cultured relative is Sterolibacterium denitrificans Chol-1S^T (94.6% similarity of the 16S rRNA genes), a cholesterol-oxidizing, denitrifying bacterium. Strain G5G6 possesses the benzylsuccinate synthase A ( bssA ) gene encoding the α-subunit of Bss, which catalyzes the first step in anaerobic toluene degradation. The deduced BssA amino acid sequence is closely related to those of Azoarcus and Thauera species, which also belong to the Betaproteobacteria . Strain G5G6 is the first toluene-degrading, iron-reducing bacterium that does not belong to the Geobacteraceae within the Deltaproteobacteria . Based on phylogenetic and physiological comparison, strain G5G6 could not be assigned to a described species. Therefore, strain G5G6 (DSMZ 19032^T=JCM 14632^T) is a novel taxon of the Betaproteobacteria . We propose the name Georgfuchsia toluolica gen. nov., sp. nov.     

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.