Filling the gap - COI barcode resolution in eastern Palearctic birds

Background

Many fish species experience long periods of fasting in nature often associated with seasonal reductions in water temperature and prey availability or spawning migrations. During periods of nutrient restriction, changes in metabolism occur to provide cellular energy via catabolic processes. Muscle is particularly affected by prolonged fasting as myofibrillar proteins act as a major energy source. To investigate the mechanisms of metabolic reorganisation with fasting and refeeding in a saltwater stage of Atlantic salmon (Salmo salar L.) we analysed the expression of genes involved in myogenesis, growth signalling, lipid biosynthesis and myofibrillar protein degradation and synthesis pathways using qPCR.

Results

Hierarchical clustering of gene expression data revealed three clusters. The first cluster comprised genes involved in lipid metabolism and triacylglycerol synthesis (ALDOB, DGAT1 and LPL) which had peak expression 3-14d after refeeding. The second cluster comprised ADIPOQ, MLC2, IGF-I and TALDO1, with peak expression 14-32d after refeeding. Cluster III contained genes strongly down regulated as an initial response to feeding and included the ubiquitin ligases MuRF1 and MAFbx, myogenic regulatory factors and some metabolic genes.

Conclusion

Early responses to refeeding in fasted salmon included the synthesis of triacylglycerols and activation of the adipogenic differentiation program. Inhibition of MuRF1 and MAFbx respectively may result in decreased degradation and concomitant increased production of myofibrillar proteins. Both of these processes preceded any increase in expression of myogenic regulatory factors and IGF-I. These responses could be a necessary strategy for an animal adapted to long periods of food deprivation whereby energy reserves are replenished prior to the resumption of myogenesis.     

Effect of N-acetylaspartic acid on the diffusion coefficient of water: a proton magnetic resonance phantom method for measurement of osmolyte-obligated water

N-acetyl-L-aspartic acid (NAA) is an amino acid present in the vertebrate brain that is synthesized and stored primarily in neurons, although it cannot be hydrolyzed in these cells. Nonetheless, neuronal NAA is dynamic and turns over more than once each day by cycling, via extracellular fluids (ECF), between neurons and catabolic compartments in oligodendrocytes. One important role of the NAA intercompartmental cycle appears to be osmoregulatory, and in this role it may be the primary mechanism for the removal of metabolic water, against a water gradient, from myelinated neurons. However, the number of water molecules that might be cotransported to ECF per NAA molecule released is as yet unclear. In this investigation, using a proton nuclear magnetic resonance method and diffusion measurements at two magnetic field strengths on water and NAA phantoms in vitro, the effect of NAA on the diffusion coefficient of water has been measured, and a ratio (K) of obligated water molecules per molecule of NAA has been determined. For NAA measured at 100mM and 3 Tesla K=24 and at 7 Tesla K=14. Based on these results, apparent K(NAA) varies inversely with field strength, and with a computed field strength factor of 2.55mmol water/unit Tesla, K(NAA) in the absence of any applied magnetic field strength would be 32.     

Expression of the Auxin-Inducible GH3 Promoter/GUS Fusion Gene as a Useful Molecular Marker for Auxin Physiology

Expression of the GH3 promoter/GUS reporter (GH3/GUS) gene intransgenic tobacco is silent in most vegetative tissues andorgans, but can be specifically induced by auxin in all celltypes throughout the plant, indicating that auxin is a limitingfactor for activation of the GH3/GUS gene. In the absence ofexogenous auxin, expression of the GH3/GUS gene either correlateswith physiological events which are presumably mediated by auxinor occurs in cells where relatively high levels of endogenousauxin are expected. For example, the GH3/GUS gene is expressedin dormant lateral buds, tips of adventitious roots, and stemparenchyma cells where adventitious roots are initiating. TheGH3/GUS gene is activated at the cut surface nearest the tipof a leaf from which a strip of tissue has been excised, andin the basal end of an excised shoot segment. Also, the GH3/GUSgene is expressed predominantly in the lower side of a gravistimulatedshoot and in the dark side of a unilateral light-stimulatedshoot. Furthermore, the expression pattern of the GH3/GUS geneis similar to the distribution pattern of ¹⁴C-IAA that is appliedat the apical end of the gravistimulated shoot. Thus, the resultsreported here provide additional support for a crucial roleof auxin in shoot gravi- and photo-tropisms and adventitiousroot formation. Furthermore, the data presented in this reportalso indicate that expression of the GH3/GUS gene is an excellentmolecular marker for studying auxin transport and for monitoringchanges in either auxin concentration or cellular sensitivityto auxin in planta. ¹ This work was supported by NASA grant NAG10-0189 and a subgrantof NASA NAGW-1197 to YL, and NSF grant IBN9003956 to TG andGH.