Myostatin is an inhibitor of myogenic differentiation

Myostatin (MSTN), atransforming growth factor (TGF)- superfamily member, has been shownto negatively regulate muscle growth by inhibiting muscle precursorcell proliferation. Here, we stably transfectedC₂C₁₂ cells with mouse MSTN cDNA to investigateits possible role in myoblast differentiation. We found that MSTN cDNAoverexpression reversibly inhibits the myogenic process by downregulating mRNA levels of the muscle regulatory factors myoD andmyogenin, as well as the activity of their downstream target creatinekinase. Taking into consideration that MSTN expression duringdevelopment is restricted to muscle, our results suggest that MSTNprobably regulates myogenic differentiation by an autocrine mechanism.

     

Centaurea molesworthiae sp. nov. (Cardueae,Compositae) from southwest Spain

Centaurea molesworthiae E. López, Devesa & García Rojas (Cardueae, Compositae), a new species from southwest Spain is described and illustrated. The morphological variability of C. molesworthiae and the three closest species, C. prolongoi, C. crocata and C. occasus is analyzed and discussed. The chromosome number (2n = 40) of this new species is reported for the first time.     

First confirmation of a native bird-pollinated plant in Europe

The pollination of Anagyris foetida L. (Fabaceae), a Mediterranean species that is a relict of the Tertiary, was studied in two populations of SW Spain over a three-year period. Numerous censuses of birds and insects were carried out, the floral nectar was quantified, and specific tests were performed to determine the pollinators' pollen load, the pollen's effective transfer to the pistil, and spontaneous self-pollination. The most important pollinators were three species of passeriforms – Phylloscopus collybita Vieillot, Sylvia atricapilla L. and S. melanocephala Gmelin– a result coherent with findings in populations of S and E Spain. The negligible existence of insect visitors and pollinators of A. foetida flowers could be explained by the early flowering of this species during the autumn–winter, coinciding with the coolest and wettest months of the year (cold, high winds, almost daily mists that persist until nightfall, and above all, abundant rainfall). The pollen loads carried by the birds were high, as were also the loads transferred to the pistil. The fruit-set of bagged flowers was very low, evidence of the plant's need for the birds as pollinators. This is the first proof of the existence of a native European bird-pollinated plant, since besides its peculaliarities (flowers odourless, pseudotubular, with no landing platform, pendulous, diurnal populations were mainly pollinated by three passeriform species.     

Sexual reproduction in someScrophularia species (Scrophulariaceae) from the Iberian Peninsula and the Balearic Islands

The reproductive biology of someScrophularia species in the Iberian Peninsula and Balearic Islands has been studied. Levels of fruit-set in bagged and unbagged inflorescences, the production of seeds/capsule, the effectiveness of seed-set following cross-pollination in the genus and the pollen/ovule ratios have been analyzed.Some observations on floral and reproductive biology in some species ofScrophularia from the Iberian Peninsula and Balearic Islands. II. For first part seeOrtega Olivencia & Devesa 1993.     

Metabolic and hormonal parameters after insulin-induced hypoglycemia in man, comparison between biosynthetic human insulin and purified pork insulin

Although clinically undistinguishable, some authors have found important differences in the counterregulatory response between Biosynthetic Human Insulin (BHI) and Purified Pork Insulin (PPI). To reassess the problem 10 healthy volunteers of both sexes underwent paired iv insulin tolerance test with both BHI and PPI (0.10 U/kg b.w.). To check the humoral response the variations of glucose, free fatty acids (FFA), prolactin, growth hormone, ACTH and plasma renin activity were evaluated. Blood glucose depression and further recovery by BHI and PPI administration paralleled each other, so were, prolactin, FFA, and plasma renin activity. A slight section of ACTH, and GH was observed under BHI challenge. There were not statistically significant differences between both insulins on any of the six parameters studied. The data do not confirm earlier published reports indicating hormonal and metabolic differences between human and porcine insulin.     

Steroids and neuroendocrine function in anorexia nervosa

Anorexia nervosa is a primarily psychiatric syndrome of self-induced weight loss due to an intense fear of becoming obese. Numerous endocrine abnormalities occur in anorexia nervosa patients, and in many respects these alterations reflects the endocrinology of reduced energy intake. However, the basic mechanisms of those alterations are far from being understood. In an attempt to understand the disrupted mechanisms of the hypogonadotropic hypogonadism of the anorectic state, we studied 10 anorectic women in the acute phase of their illness; all met the DSM III criteria. On each patient, two tests were performed with either saline as control or infusion of the opioid antagonist naloxone, and both LH and FSH levels were measured. Four mg of naloxone as bolus was used, followed by a naloxone infusion of 2 mg/h for 4 h. Compared with the pattern of normal women, naloxone did not increase in the anorectic patients either LH or FSH levels nor pulsatility. This result suggests that endogenous opioid peptides are not implicated in the low gonadotropic situation of anorexia nervosa. An alternative explanation could be that the low estrogenic "milieu" of these patients could mask the opioid action. To test this second possibility, another group of 7 anorectic women after partial weight recovery were challenged with estrogen administration. Compared with the pattern of normal women volunteers, all the anorectic patients but one presented an abnormal response in both LH and FSH levels after estrogen administration. In fact, the negative feedback and the delayed positive feedback of LH after estrogen were absent in these patients. Interestingly enough, the only patient with near-normal LH response to estrogen was considered fully recovered by the Psychiatric Unit. Several alterations in the hypothalamic-pituitary-adrenal axis has been reported in anorexia nervosa. Seven anorectic patients and 7 aged-matched women were challenged by ACTH 1-24, 250 micrograms (i.v.) and the ratio of increments in adrenal steroid products to precursors monitored. ACTH-induced increments in cortisol with respect to increments in 17-OH-progesterone was similar in anorectics and controls. On the contrary, the ratio of increments of androstenedione with respect to increments in 17-OH-progesterone were greater in anorexia nervosa than controls. These results suggest that in anorexia nervosa the 11-beta-21-alpha-hydroxylase system is normal but a deficient 17-20 desmolase system is present. Finally, the altered pattern of GH secretion in anorexia was studied using GHRH (1 microgram/kg) as stimulus of pituitary GH secretion.(ABSTRACT TRUNCATED AT 400 WORDS)     

Myostatin expression is regulated by underfeeding and neonatal programming in rats

Confusing results have been reported regarding the influence of nutritional status on myostatin levels. Some studies indicate that short-term fasting results in increased myostatin mRNA levels in skeletal muscle, evident in several species. In contrast, other studies have demonstrated either a decrease or no change in myostatin levels during fasting. In the present study, we investigated the effect of different patterns of food deprivation on muscle myostatin expression in both newborn and adult rats. Adjustment of litter size in neonatal rats is a well-established model to study the effect of early overfeeding or underfeeding on body composition and in this study resulted in modifications in the pattern of muscle myostatin expression. Rat pups growing in large litters (22–24 newborns) showed a decrease in muscle myostatin mRNA and protein levels at 24 days of age. Interestingly, these effects were maintained at 60 days of age despite rats having free access to food since weaning, thus suggesting that changes in myostatin expression induced by neonatal reduction of food intake are long-lasting. In contrast, no changes in myostatin mRNA levels were observed in adult rats when food intake was decreased during 7 days by either food restriction or central leptin treatment. Similar results were obtained when food restriction was maintained in adult rats for a longer period (7 weeks), despite significant muscle loss. Overall, these data suggest that myostatin gene expression is programmed by nutritional status in neonatal life.     

Myostatin regulates cell survival during C2C12 myogenesis

During the myogenic process in vitro, proliferating myoblasts withdraw irreversible from the cell cycle, acquire an apoptosis-resistant phenotype, and fuse into mature myotubes. The key factor regulating both myocyte cell cycle exit and viability during this transition is the the cyclin-dependent kinase inhibitor p21(cip1). Here we show that the expression of myostatin, a TGF-beta superfamily member known to act as a negative regulator of muscle growth, is upregulated in the course of C2C12 cells myogenesis. We also show that transient transfection of C2C12 myobasts with an expression vector encoding mouse myostatin cDNA efficiently inhibits cell proliferation. Paradoxically, myostatin cDNA overexpression also enhances the survival of differentiating C2C12 myocytes, probably by a mechanism involving, at least in part, upregulation of p21(cip1) mRNA. Our results suggest that myostatin role in myogenesis is more complex than initially suggested and involves another level of regulation apart from inhibition of myoblast proliferation.     

The CDK regulators Cdh1 and Sic1 promote efficient usage of DNA replication origins to prevent chromosomal instability at a chromosome arm

Robustness and completion of DNA replication rely on redundant DNA replication origins. Reduced efficiency of origin licensing is proposed to contribute to chromosome instability in CDK-deregulated cell cycles, a frequent alteration in oncogenesis. However, the mechanism by which this instability occurs is largely unknown. Current models suggest that limited origin numbers would reduce fork density favouring chromosome rearrangements, but experimental support in CDK-deregulated cells is lacking. We have investigated the pattern of origin firing efficiency in budding yeast cells lacking the CDK regulators Cdh1 and Sic1. We show that each regulator is required for efficient origin activity, and that both cooperate non-redundantly. Notably, origins are differentially sensitive to CDK deregulation. Origin sensitivity is independent on normal origin efficiency, firing timing or chromosomal location. Interestingly, at a chromosome arm, there is a shortage of origin firing involving active and dormant origins, and the extent of shortage correlates with the severity of CDK deregulation and chromosome instability. We therefore propose that CDK deregulation in G1 phase compromises origin redundancy by decreasing the number of active and dormant origins, leading to origin shortage and increased chromosome instability.