Rat fat-cells have three types of adenosine receptors (Ra, Ri and P). Differential effects of pertussis toxin.

Activation of rat adipocyte R1 adenosine receptors by phenylisopropyladenosine (PIA) decreased cyclic AMP and lipolysis; this effect was blocked in cells from pertussis-toxin-treated rats. In contrast, the ability of 2',5'-dideoxyadenosine to decrease cyclic AMP was not affected by pertussis-toxin treatment. Addition of adenosine deaminase to the medium in which adipocytes from control animals were incubated resulted in activation of lipolysis. Interestingly, adipocytes from toxin-treated rats (which had an already increased basal lipolysis) responded in an opposite fashion to the addition of adenosine deaminase, i.e. the enzyme decreased lipolysis, which suggested that adenosine might be increasing lipolysis in these cells. Studies with the selective agonists N-ethylcarboxamidoadenosine (NECA) and PIA indicated that adenosine increases lipolysis and cyclic AMP accumulation in these cells and that these actions are mediated through Ra adenosine receptors. Adenosine-mediated accumulation of cyclic AMP was also observed in cells preincubated with pertussis toxin (2 micrograms/ml) for 3 h. In these studies NECA was also more effective than PIA. Our results indicate that there are three types of adenosine receptors in fat-cells, whose actions are affected differently by pertussis toxin, i.e. Ri-mediated actions are abolished, Ra-mediated actions are revealed and P-mediated actions are not affected.     

Circadian and seasonal cortico-medullary variations in pinealocyte nuclear size. A comparative statistical analysis.

Circadian and seasonal variations were observed in the karyometric index of pinealocytes in the cortical and medullary regions of the distal pineal body. The study involved 70 Wistar rats over a 24-hour interval (0:6, 10:00, 14:00, 18:00, 22:00, 02:00, 06:00 h) during two natural photoluminous periods, i.e. late summer (Long photoperiod) and Winter (Short photoperiod). The results show a difference between the high and low points of both photoperiods. Cortico-medullary differences are found at different times of day during long photoperiod (0:6; 10:00; 14:00 and 18:00 h.) and short photoperiod (14:00; 22:00 and 02:00 h.). The variance analyses between nuclear volume and point-time and between nuclear volume, point-time and location are significative. A high correlation between circadian rhythms and volumetric variations in both layers and photoperiod are found. The results also show significant differences in cortico-medullary karyometric indices between both seasons as well as between the diurnal and nocturnal hours of both photoperiods. It is suggested that the pineal body of the rat is influenced by circadian and seasonal photoperiod and may have groups of cells with different functional characteristics, depending on their location within the gland.     

Differences in the rotation spectra of mouse oocytes and zygotes

Rotation spectra of mouse oocytes, zygotes and embryos in the two-cell stage under the influence of high-frequency rotating fields were studied. The characteristic frequency (fc1) of cells isolated from superovulated + mated mice is different from that of oocytes. This was attributed to an increase in the membrane resistance and, less probably, to a change in the zona pellucida conductivity. The rotation spectra can be used to differentiate between non-fertilized and fertilized eggs. A theoretical interpretation of the measured spectra and simulation of the changes caused by fertilization is given.     

The stability and formation of native proteins from unfolded monomers is increased through interactions with unrelated proteins

The intracellular concentration of protein may be as high as 400 mg per ml; thus it seems inevitable that within the cell, numerous protein-protein contacts are constantly occurring. A basic biochemical principle states that the equilibrium of an association reaction can be shifted by ligand binding. This indicates that if within the cell many protein-protein interactions are indeed taking place, some fundamental characteristics of proteins would necessarily differ from those observed in traditional biochemical systems. Accordingly, we measured the effect of eight different proteins on the formation of homodimeric triosephosphate isomerase from Trypanosoma brucei (TbTIM) from guanidinium chloride unfolded monomers. The eight proteins at concentrations of micrograms per ml induced an important increase on active dimer formation. Studies on the mechanism of this phenomenon showed that the proteins stabilize the dimeric structure of TbTIM, and that this is the driving force that promotes the formation of active dimers. Similar data were obtained with TIM from three other species. The heat changes that occur when TbTIM is mixed with lysozyme were determined by isothermal titration calorimetry; the results provided direct evidence of the weak interaction between apparently unrelated proteins. The data, therefore, are strongly suggestive that the numerous protein-protein interactions that occur in the intracellular space are an additional control factor in the formation and stability of proteins.     

Tempo and mode of early gene loss in endosymbiotic bacteria from insects

Background  

Understanding evolutionary processes that drive genome reduction requires determining the tempo (rate) and the mode (size and types of deletions) of gene losses. In this study, we analysed five endosymbiotic genome sequences of the gamma-proteobacteria (three different Buchnera aphidicola strains, Wigglesworthia glossinidia, Blochmannia floridanus) to test if gene loss could be driven by the selective importance of genes. We used a parsimony method to reconstruct a minimal ancestral genome of insect endosymbionts and quantified gene loss along the branches of the phylogenetic tree. To evaluate the selective or functional importance of genes, we used a parameter that measures the level of adaptive codon bias in E. coli (i.e. codon adaptive index, or CAI), and also estimates of evolutionary rates (Ka) between pairs of orthologs either in free-living bacteria or in pairs of symbionts.     

Changes in cumulus-oocyte complexes of pregnant and non-pregnant camels (Camelus dromedarius) during maturation in vitro

The aim of the present study was to examine the cumulus morphology and the oocyte chromatin quality of camel cumulus-oocyte complexes (COCs) at the time of recovery, and to monitor changes in oocyte chromatin configuration and apoptosis in cumulus cells from camel COCs during in vitro maturation (IVM) (0, 12, 24, 32, 36, 42, and 48 p.IVM) depending on pregnancy of donors. A total of 1023 COCs were isolated from sliced ovaries after slaughtering of 47 pregnant and 43 non-pregnant camels in an abattoir. The mean number of COCs per donor was 10.3 in pregnant and 12.5 in non-pregnant donors. The cumulus morphology of COCs was independent of the type of donor and was divided in COCs with compact (26.9 and 28%), dispersed (39.3 and 46%), corona radiata cumulus investment (27.9 and 21.7%) and without cumulus (6 and 4.2%), respectively for pregnant and non-pregnant donors. The highest proportion of COCs exhibited dispersed cumulus (P<0.05). Oocytes with meiotic stages of diplotene >50% were found only in compact (55 and 56.5%) and in dispersed COCs (58.4 and 60%), respectively for pregnant and non-pregnant donors. During IVM (0-48h) the first significant onset of specific meiotic stages were different in oocytes from pregnant donors: metaphase 1 (24-32h), metaphase 2 (36-42h), versus oocytes from non-pregnant donors: metaphase 1 (24h), metaphase 2 (32-48h) (P<0.05). The level of apoptotic cells in cumuli of matured COCs increased during IVM and was higher in matured COCs from non-pregnant donors for each time point during IVM (P<0.01). Camel oocytes meiosis during IVM is accompanied by a drastic increase of apoptosis in the surrounding cumulus cells 0-32 and 0-24h during IVM, respectively for pregnant and non-pregnant donors. The oocytes of pregnant camels require 36h of maturation to reach levels of >50% metaphase 2 stage in comparison to oocytes from non-pregnant donors where 32h are sufficient. The earlier onset of apoptosis in the COCs derived from non-pregnant donors possibly determines the faster progression of the oocytes through the final stages of meiosis.     

The influence of somatotropin, prolactin and insulin on granulosa cells from bovine atretic follicles

An influence of somatotropin, prolactin and insulin on destructive processes in bovine granulosa cells from small antral follicles following atresia in vivo was studied in vitro. As compared to control, the addition of the studied hormones to serum-free suspension system was shown to result in increase in number of cells without signs of chromosome degeneration after 24 and 48 hrs of incubation. The revealed inhibitory action of somatotropin, prolactin and insulin on chromatin degeneration in granulosa cells was not due to the hormonal influence on proliferative activity of the cells. The stimulatory action of insulin on the viability and estrogen-secretory activity of granulosa cells cultured for 1 day was also found. At the same time, somatotropin and prolactin did not affect the estradiol and progesterone production by the cells. The data obtained suggest that the inhibitory action of somatotropin and prolactin on destructive processes in cultured granulosa cells is not related to the hormonal regulation of the steroidogenic activity of the cells, whereas the similar action of insulin may be partially due to its stimulatory influence on the estradiol secretion.     

Prolactin-binding activity of bovine granulosa cells on luteinization and exposure to somatotropin in vitro

The influence of luteinization and bovine somatotropin (ST, 5-50 ng/ml) during cultivation of bovine granulosa cells on their ability to bind [125I]-labeled bovine prolactin (PRL) was studied. On the second day of cultivation in serumfree medium, granulosa cells from immature antral follicles underwent spontaneous luteinization, in both the absence and presence of ST. The level of [125I]-PRL specific binding to cells increased after two days of cultivation, with a negative correlation being revealed between estradiol production by the cells and their PRL-binding activity. At the same time, the addition of ST to the culture medium had no effect on the level of [125I]-PRL specific binding to native and luteinizing granulosa cells. The findings suggest a stimulatory influence of the luteal differentiation process on the PRL-binding activity of bovine granulosa cells, this influence is independent of the action of ST.