Dynamic myosin phosphorylation regulates contractile pulses and tissue integrity during epithelial morphogenesis

Apical constriction is a cell shape change that promotes epithelial bending. Activation of nonmuscle myosin II (Myo-II) by kinases such as Rho-associated kinase (Rok) is important to generate contractile force during apical constriction. Cycles of Myo-II assembly and disassembly, or pulses, are associated with apical constriction during Drosophila melanogaster gastrulation. It is not understood whether Myo-II phosphoregulation organizes contractile pulses or whether pulses are important for tissue morphogenesis. Here, we show that Myo-II pulses are associated with pulses of apical Rok. Mutants that mimic Myo-II light chain phosphorylation or depletion of myosin phosphatase inhibit Myo-II contractile pulses, disrupting both actomyosin coalescence into apical foci and cycles of Myo-II assembly/disassembly. Thus, coupling dynamic Myo-II phosphorylation to upstream signals organizes contractile Myo-II pulses in both space and time. Mutants that mimic Myo-II phosphorylation undergo continuous, rather than incremental, apical constriction. These mutants fail to maintain intercellular actomyosin network connections during tissue invagination, suggesting that Myo-II pulses are required for tissue integrity during morphogenesis.National Institute of General Medical Sciences (U.S.) (Transgenic RNAi Project at Harvard Medical School, (R01-GM084947)

Gut Hormones and Regulation of Food Intake in Birds

Gut hormones act as appetite regulatory hormones in mammals. For example, the hunger hormone ghrelin, which is released from the stomach before food intake, stimulates appetite. In contrast, satiety hormones such as cholecystokinin, glucagon-like peptide-1, and peptide YY, which are released from the intestines after food intake, suppress appetite. The effects of these peptides on food intake have been shown to be similar in both mammals and fishes. However, evidence suggests that the physiological roles of these gut hormones may be different between birds and other vertebrates. This review summarizes the current information on the roles of gut hormones in the regulation of food intake in birds, especially in chickens

Myostatin Increases Smad2 Phosphorylation and Atrogin-1 Expression in Chick Embryonic Myotubes

Skeletal muscle mass is an important trait in poultry meat production. In mammals, myostatin, a negative regulator of skeletal muscle growth, activates Smad transcription factors and induces the expression of atrogin-1 by regulating the Akt/FOXO pathway. Although the amino acid sequence of chicken myostatin is known to be completely identical to its mammalian counterpart, previous studies in chicken skeletal muscles have implied that the physiological roles of chicken myostatin are different from those of mammals. Furthermore, it remains to be elucidated whether myostatin affects cellular signaling factors and atrogin-1 expression. In this study, using chick embryonic myotubes, we found that myostatin significantly increased the phosphorylation rate of Smad2 and mRNA levels of atrogin-1. No significant change was observed in the phosphorylation of Akt and FOXO1. These in vitro results suggest that the molecular mechanisms underlying myostatin-induced expression of atrogin-1 might be different between chickens and mammals

Effects of Dietary Fat Levels on Nutrient Digestibility at Different Sites of Chicken Intestines

The present study was conducted to investigate the effects of varying dietary fat levels (3%-10%) on the digestibilities of crude protein, crude fat (CF), nitrogen-free extract and ash at different sites of fistulized chicken intestines. Chickens were fistulized to either the middle part of the jejunum (MJ), the distal end of the jejunum (DJ), the middle part of the ileum, the distal end of the ileum or the distal end of the rectum. Intestinal digesta were collected from each site of intestine, and contents of crude protein, crude fat, nitrogen-free extract and ash were measured. The true digestibility of crude protein in intestinal digesta at MJ in the 10% CF group was significantly lower than that in other groups. The digestibility of crude fat in intestinal digesta at MJ in the 10% CF group was also significantly lower than that in other groups. The digestibility of nitrogen-free extract at MJ and DJ in the 10% CF group was significantly lower than that in other groups. There were no significant differences in digestibility of ash among groups. These results clearly demonstrate that dietary fat levels influence the digestibility of protein, fat, and carbohydrate at MJ in chicken

Effects of Dietary Protein Levels on the Nutrient Digestibility at Different Sites of Chicken Intestines

The present study was conducted to investigate the effects of dietary protein levels (0, 10, 15, 20 and 30%) on the digestibilities of crude protein, crude fat, nitrogen-free extract and ash at different sites of fistulized chicken intestines. Chickens were fistulized to either the middle part of jejunum (MJ), distal end of jejunum (DJ), middle part of ileum, distal end of ileum or distal end of rectum. Intestinal digesta were collected from each site of intestine, and contents of crude protein, crude fat, nitrogen-free extract and ash were measured. The true digestibility of crude protein in intestinal digesta at MJ and DJ in the 10% group and at MJ in the 15% group was significantly lower than those in the 30% group. The digestibility of crude fat in intestinal digesta at MJ and DJ in both the 0 and 10% groups were significantly lower than those in other groups. The digestibility of nitrogen-free extract at MJ and DJ in the 0% group and at MJ in the 10% group were significantly lower than those in other groups. The digestibility of ash at all sites of intestines in the 0% group showed the lowest value among groups. These results clearly demonstrate that dietary protein level influences the digestibilities of protein, fat, carbohydrate and ash in chicken intestines

Effects of Dietary Protein Levels on Amino Acid Digestibility at Different Sites of Male Adult Chicken Intestines

The present study was conducted to investigate the effects of varying dietary protein levels on amino acid digestibility at different sites of fistulized chicken intestines. Chickens were fistulized to either the middle part of the jejunum (MJ), the distal end of the jejunum, the middle part of the ileum, the distal end of the ileum or the distal end of the rectum (DR). Intestinal digesta were collected from each site of the intestine, and contents of amino acids were measured. The true digestibilities of all amino acids in intestinal digesta at MJ were significantly lower than those at DR in the 10% protein group. In the 15% protein group, the true digestibilities of Asp, Thr, Glu, Pro, Gly, Val, Met and Ile in intestinal digesta at MJ were significantly lower than those at DR. The true digestibility of Ser in intestinal digesta at MJ was significantly lower than that at DR in the 20% protein group. In the 30% protein group, there was no significant difference in the true digestibilities of amino acids in intestinal digesta between the sites of the intestine. The true digestibilities of all amino acids in intestinal digesta at MJ in the 10% protein group were significantly lower than those in other groups. These results clearly demonstrated that dietary protein levels influence amino acid digestibility at MJ in chickens