Evidence for a role of protein kinase C zeta subspecies in maturation of Xenopus laevis oocytes.

A number of studies have demonstrated the activation of phospholipase C-mediated hydrolysis of phosphatidylcholine (PC-PLC) both by growth factors and by the product of the ras oncogene, p21ras. Evidence has been presented indicating that the stimulation of this phospholipid degradative pathway is sufficient to activate mitogenesis in fibroblasts as well as that it is sufficient and necessary for induction of maturation in Xenopus laevis oocytes. However, the mechanism whereby PC-PLC transduces mitogenic signals triggered by growth factors or oncogenes remains to be elucidated. In this study, data are presented that show the involvement of protein kinase C zeta subspecies in the channelling of the mitogenic signal activated by insulin-p21ras-PC-PLC in Xenopus oocytes as well as the lack of a critical role of protein kinase C isotypes alpha, beta, gamma, delta, and epsilon in these pathways.     

Thymosin-beta 4 gene. Preliminary characterization and expression in tissues, thymic cells, and lymphocytes

A cDNA for rat thymosin-beta 4 was used to investigate the expression of this gene in different tissues, thymic cells, and lymphocytes. Hybridization analysis of total RNA from 13 rat tissues demonstrated the presence of an 800 nucleotides-long mRNA in all the tissues surveyed, with the highest levels in spleen, thymus, and lung. Examination of thymic cells showed that the thymosin-beta 4 gene is predominantly expressed in thymocytes. The thymosin-beta 4 mRNA was also studied in Ig+ and Ig- lymphocytes, being fourfold more abundant in Ig- than Ig+ splenic lymphocytes, whereas similar levels were found in both types of blood cells. The analysis of RNA from T cells at different maturation stages evidenced slight differences in their thymosin-beta 4 mRNA content, indicating that thymosin-beta 4 gene expression is not clearly related to the differentiation process of T cells. All these results do not support the roles for thymosin-beta 4 in cellular immunity and differentiation of lymphoid cells, suggesting a more general function for this peptide. Preliminary characterization of the human beta 4 gene by restriction analysis disclosed a complicated pattern consistent with multiple genes and/or introns. The analysis of genomic DNA from different species ranging from humans to Escherichia coli showed that this gene is only highly conserved in mammals.     

Mutations Modulating Raf Signaling in Drosophila Eye Development

The R7 fate is specified during Drosophila eye development by an inductive signal transduced intracellularly via the Raf kinase. We have performed a genetic screen for dominant mutations that alter the efficiency with which cells respond to a constitutively activated Raf kinase. Such mutations may affect genes involved in signal transduction downstream of Raf. We have isolated 44 mutations that define eight genes. One of these encodes a mitogen-activated protein kinase homologue; another is a putative target gene of this signaling pathway. We present the results of this screen in detail, as well as a preliminary genetic analysis of the six loci still to be characterized molecularly.     

Pollen-ovule ratio,pollen size,and breeding system in Astragalus (Fabaceae) subgenus Epiglottis: a pollen and seed allocation approach

The correlation between pollen/ovule (P/O) ratio and breeding system has generally been accounted for either on the basis that P/O reflects pollination efficiency, or in terms of the sex allocation theory. The following were assessed for taxa belonging to genus Astragalus subgenus Epiglottis: 1) Degree of correlation between P/O and the breeding system, measured by means of autofertility; 2) The absence or existence of correlation between P/O and pollen grain size; and 3) The ability of various theories to account for the results obtained. Results showed a minimal correlation between P/O and autofertility, and between P/O and pollen grain size in the taxa studied. Analysis of these results in terms of the sex allocation theory enabled this correlation to be explained as a function of the variation existing between taxa with respect to the resources invested in each pollen grain and in each ovule. The predictive capacity of this theory, which has moreover proven valuable in explaining the structural peculiarities of the androecium in these taxa, was also highlighted. The type of self-pollination applicable was also discussed, as was the phenotypic model of selection of self-fertilization considered most plausible for these taxa.     

Inhibition of protein kinase C zeta subspecies blocks the activation of an NF-kappa B-like activity in Xenopus laevis oocytes.

Nuclear factor kappa B (NF-kappa B) plays a critical role in the regulation of a large variety of cellular genes. However, the mechanism whereby this nuclear factor is activated remains to be determined. In this report, we present evidence that in oocytes from Xenopus laevis, (i) ras p21- and phospholipase C (PLC)-mediated phosphatidylcholine (PC) hydrolysis activates NF-kappa B and (ii) protein kinase C zeta subspecies is involved in the activation of NF-kappa B in response to insulin/ras p21/PC-PLC. Thus, the microinjection of either ras p21 or PC-PLC, or the exposure of oocytes to insulin, promotes a significant translocation to the nucleus of an NF-kappa B-like activity. This effect is not observed when oocytes are incubated with phorbol myristate acetate or progesterone, both of which utilize a ras p21-independent pathway for oocyte activation. These data strongly suggest a critical role of the insulin/ras p21/PC-PLC/protein kinase C zeta pathway in the control of NF-kappa B activation.     

Inequalities in income and long-term disability in Spain: analysis of recent hypotheses using cross sectional study based on individual data.

OBJECTIVE: To compare the relation between inequalities in long-term disability and income in the 17 regions of Spain. DESIGN: Data were taken from the survey on impairments, disabilities, and handicaps that was carried out in Spain in 1986. For each region the inequality in long-term disability associated with income was calculated as the odds ratio associated with reducing monthly household income by 10,000 pesetas (about Ponds 50) (estimate of effect of inequality of income) and the odds ratio for the inequality in long-term disability between those at the bottom and those at the top of the income hierarchy (relative index of inequality). MAIN OUTCOME MEASURE: Prevalence of long-term disability. RESULTS: Five of the eight regions where lowering income had a greater effect on long-term disability were among those with the lowest income per head, while six of the remaining nine regions where the effect was smaller were among those with the highest income per head. Three regions with the highest estimate of relative index of inequality had the highest estimate of effect, and another three regions with the lowest estimate of relative index of inequality had the lowest estimate of effect. In contrast, the relative position of the remaining 11 regions varied from one measure to another. CONCLUSIONS: These results support the theory that additional increments in material wellbeing have a negligible effect on health in countries with high socioeconomic development. However, inequality in income distribution did not determine inequality in health between those at the bottom and those at the top of the income hierarchy in many Spanish regions.     

Susceptibility of heterochromatin to aphidicolin-induced chromosomal breakage

The distribution of aphidicolin-induced chromosomal lesions was analyzed to determine the relative breakage susceptibility of euchromatin and heterochromatin in the cactus mouse, Peromyscus eremicus. The observed breakage was tested against expected distributions corresponding to the karyotypic proportions of autosomal euchromatin, autosomal heterochromatin, X-chromosomal euchromatin, and X-chromosomal heterochromatin. The distribution of induced breakage was independent of sex but dependent on the individual. In all individuals, there was a highly significant (P0.0001) deficiency in the number of breaks observed as compared to expected in autosomal heterochromatin. Sparse observations in the X chromosome and the absence of breaks in the Y chromosome precluded valid statistical tests of the sex-chromosomal distribution of induced breakage. These data indicate that the autosomal heterochromatin of Peromyscus is resistant to aphidicolin-induced chromosomal breakage and argue against a simple relationship between late replication and a general mechanism for chromosomal fragility.     

Mechanisms of appearance of the Pasteur effect in Saccharomyces cerevisiae: inactivation of sugar transport systems.

Saccharomyces cerevisiae does not show a noticeable Pasteur effect (activation of sugar catabolism by anaerobiosis) when growing with an excess of sugar and nitrogen source, but it does do so after exhaustion of the nitrogen source in the medium (resting state). We have found that this different behavior of growing and resting S. cerevisiae seems due to differences in the contribution of respiration to catabolism under both states. Growing S. cerevisiae respired only 3 to 20% of the catabolized sugar, depending on the sugar present; the remainder was fermented. In contrast, resting S. cerevisiae respired as much as 25 to 100% of the catabolized sugar. These results suggest that a shift to anaerobiosis would have much greater energetic consequences in resting than in growing S. cerevisiae. In resting S. cerevisiae anaerobiosis would strongly decrease the formation of ATP; as a consequence, various regulatory mechanisms would switch on, producing the observed increase of the rate of glycolysis. The greater significance that respiration reached in resting cells was not due to an increase of the respiratory capacity itself, but to a loss of fermentation which turned respiration into the main catabolic pathway. The main mechanism involved in the loss of fermentation observed during nitrogen starvation was a progressive inactivation of the sugar transport systems that reduced the rate of fermentation to less than 10% of the value observed in growing cells. Inactivation of the sugar transports seems a consequence of the turnover of the sugar carriers whose apparent half-lives were 2 to 7 h.     

Mutants of Saccharomyces cerevisiae cell division cycle defective in cytokinesis. Biosynthesis of the cell wall and morphology

The four temperature-sensitive mutants of Saccharomyces cerevisiae in the cell division cycle defective in cytokinesis (cdc, 3, 10, 11 and 12), have been analyzed with respect to the biosynthesis of the cell wall polymers. After 3 hours of incubation at the non-permissive temperature (37°C) these strains stop growing. The synthesis of glucan, mannan and chitin (wall polymers) level off in a similar time, but glucan, mannan and chitin synthases remained active for at least 4 hours.If the mutants are analyzed by transmission and scanning electron microscopy different pictures emerge. Two of the mutants cdc 10 and cdc 12, after 3 hours of incubation at 37°C present apparently normal cytoplasms and cell wall surfaces with multiple elongated buds. The other two mutants, cdc 3 and cdc 11, present a completely disarranged cytoplasmic content and damage at the level of the plasma membrane is evident.These and other observations, suggest that between the execution points of cdc 3 (0.27) and cdc 10 (0.58), essential processes in the assembly of cell membrane occur.This work was supported in part by a grant from la Comisión de Investigación Científica y Técnica of the Spanish Ministerio de Educación y Ciencia (Project no. 4593-1980).