Molecular Cloning and Construction of agp Gene Deletion-mutant in Cyanobacterium Synechocystis sp. PCC 6803

The agp gene encoding the ADP-glucose pyrophosphorylase involved in cyanobacterial glycogen synthesis was amplified by PCR. The resulting agp fragment was cloned in plasmid pUC118 to generate plasmid pUCA. Part of the fragment within the agp DNA was deleted and replaced by an erythromycin resistance cassette to generate plasmid pUCAE, which was used to transform the Synechocystis sp. PCC 6803 wild-type strain and a mutant with resistance to erythromycin was obtained. PCR analysis of the genomic DNA from the resulting mutant indicated that the appropriate deletion and insertion indeed had occurred. The cell growth and Chl a, glycogen content in the mutant showed difference from those in the wild-type strain. The obtained biomass as well as the Chl a content in the mutant strain was higher than that of the wild-type strain, which suggested that the photosynthesis efficiency in the agp(-) strain was higher than that in the wild-type strain. No glycogen was found in the mutant, providing evidence for the correction of the mutant in physiological level.

Loss of hnRNP A1 in murine skeletal muscle exacerbates high-fat diet-induced onset of insulin resistance and hepatic steatosis

Impairment of glucose(Glu)uptake and storage by skeletal muscle is a prime risk factor for the development of metabolic diseases.Heterogeneous nuclear ribonucleoprotein A1(hnRNP Al)is a highly abundant RNA-binding protein that has been implicated in diverse cellular functions.The aim of this study was to investigate the function of hnRNP A1 on muscle tissue insulin sensitivity and systemic Glu homeostasis.Our results showed that conditional deletion of hnRNP Al in the muscle gave rise to a severe insulin resistance phenotype in mice fed a high-fat diet(HFD).Conditional knockout mice fed a HFD showed exacerbated obesity,insulin resistance,and hepatic steatosis.In vitro interference of hnRNP Al in C2C12 myotubes impaired insulin signal transduction and inhibited Glu uptake,whereas hnRNP Al overexpression in C2C12 myotubes protected against insulin resistance induced by supraphysiological concentrations of insulin.The expression and stability of glycogen synthase(gysl)mRNA were also decreased in the absence of hnRNP A l.Mechanistically,hnRNP Al interacted with gys l and stabilized its mRNA,thereby promoting glycogen synthesis and maintaining the insulin sensitivity in muscle tissue.Taken together,our findings are the first to show that reduced expression of hnRNP Al in skeletal muscle affects the metabolic properties and systemic insulin sensitivity by inhibiting glycogen synthesis.