Effects of frequent machine milking and suckling in early lactation on blood plasma ion homoeostasis in high-yielding dairy cows

SUMMARY Groups of nine or ten cows were assigned, after calving, to treatments in which they were (i) machine milked three times daily (M3), (ii) machine milked six times daily (M6) or (iii) suckled three times daily in addition to being machine milked three times daily (S). Treatments were administered during the first 6 weeks postpartum. On one day, at weeks 1 and 6 postpartum, blood samples were collected from all cows at 30-min intervals between 06.00 and 13.00 h and these were analysed for plasma osmolality and plasma concentrations of Na + , K + and Cl − . Milk yield was significantly higher in suckled cows than in cows milked six times daily, but significantly lower in cows milked three times daily. In cows milked six times daily, and to a greater extent in suckled cows, there was a reduction in plasma osmolality and monovalent ion concentrations (Na + , K + and Cl − ), which could increase the susceptibility of the cows to water intoxication. Moreover, suckling or milking the cows six times daily was associated with increased fluctuations in plasma osmolality and plasma Cl − concentrations. The decrease in plasma osmolality and ion concentration and the increased variation in plasma osmolality and Cl − were probably related to increased water intake and may be indicative of a severe challenge to homoeostasis regulation

Crystal structure of the Ego1-Ego2-Ego3 complex and its role in promoting Rag GTPase-dependent TORC1 signaling

The target of rapamycin complex 1 (TORC1) integrates various hormonal and nutrient signals to regulate cell growth, proliferation, and differentiation. Amino acid-dependent activation of TORC1 is mediated via the yeast EGO complex (EGOC) consisting of Gtr1, Gtr2, Ego1, and Ego3. Here, we identify the previously uncharacterized Ycr075w-a/Ego2 protein as an additional EGOC component that is required for the integrity and localization of the heterodimeric Gtr1-Gtr2 GTPases, equivalent to mammalian Rag GTPases. We also report the crystal structure of the Ego1-Ego2-Ego3 ternary complex (EGO-TC) at 2.4 Å resolution, in which Ego2 and Ego3 form a heterodimer flanked along one side by Ego1. Structural data also reveal the structural conservation of protein components between the yeast EGO-TC and the human Ragulator, which acts as a GEF for Rag GTPases. Interestingly, however, artificial tethering of Gtr1-Gtr2 to the vacuolar membrane is sufficient to activate TORC1 in response to amino acids even in the absence of the EGO-TC. Our structural and functional data therefore support a model in which the EGO-TC acts as a scaffold for Rag GTPases in TORC1 signaling

AMP-activated protein kinase - not just an energy sensor

Orthologues of AMP-activated protein kinase (AMPK) occur in essentially all eukaryotes as heterotrimeric complexes comprising catalytic α subunits and regulatory β and γ subunits. The canonical role of AMPK is as an energy sensor, monitoring levels of the nucleotides AMP, ADP, and ATP that bind competitively to the γ subunit. Once activated, AMPK acts to restore energy homeostasis by switching on alternate ATP-generating catabolic pathways while switching off ATP-consuming anabolic pathways. However, its ancestral role in unicellular eukaryotes may have been in sensing of glucose rather than energy. In this article, we discuss a few interesting recent developments in the AMPK field. Firstly, we review recent findings on the canonical pathway by which AMPK is regulated by adenine nucleotides. Secondly, AMPK is now known to be activated in mammalian cells by glucose starvation by a mechanism that occurs in the absence of changes in adenine nucleotides, involving the formation of complexes with Axin and LKB1 on the surface of the lysosome. Thirdly, in addition to containing the nucleotide-binding sites on the γ subunits, AMPK heterotrimers contain a site for binding of allosteric activators termed the allosteric drug and metabolite (ADaM) site. A large number of synthetic activators, some of which show promise as hypoglycaemic agents in pre-clinical studies, have now been shown to bind there. Fourthly, some kinase inhibitors paradoxically activate AMPK, including one (SU6656) that binds in the catalytic site. Finally, although downstream targets originally identified for AMPK were mainly concerned with metabolism, recently identified targets have roles in such diverse areas as mitochondrial fission, integrity of epithelial cell layers, and angiogenesis