Gamma irradiation prevents compensatory hypertrophy of overloaded mouse extensor digitorum longus muscle.

Mouse extensor digitorum longus (EDL) muscle was subjected to a dose of gamma irradiation that causes reproductive death of satellite cells and/or to chronic compensatory overload, achieved by removal of the distal portion of the tibialis anterior muscle. Four weeks later the mass, fiber type percentage, and fiber size of the EDL muscle were measured. Both the irradiated + overloaded and the irradiated only EDL muscles were significantly lighter and contained significantly smaller fibers than untreated muscle or muscle subjected to chronic overload only. Overload muscle, whether irradiated or not, had a larger percentage of type IIx fibers and a smaller percentage of type IIb fibers than muscle that had not been overloaded. The results confirm that satellite cell proliferation is a prerequisite for muscle hypertrophy induced by synergist incapacitation, but it appears not to be required for the maintenance of, or change in, normal muscle fiber myosin heavy chain phenotype expression.     

Neuregulin3 alters cell fate in the epidermis and mammary gland

Background  

The Neuregulin family of ligands and their receptors, the Erbb tyrosine kinases, have important roles in epidermal and mammary gland development as well as during carcinogenesis. Previously, we demonstrated that Neuregulin3 (Nrg3) is a specification signal for mammary placode formation in mice. Nrg3 is a growth factor, which binds and activates Erbb4, a receptor tyrosine kinase that regulates cell proliferation and differentiation. To understand the role of Neuregulin3 in epidermal morphogenesis, we have developed a transgenic mouse model that expresses Nrg3 throughout the basal layer (progenitor/stem cell compartment) of mouse epidermis and the outer root sheath of developing hair follicles.     

Biochemical characterization of VlmL, a Seryl-tRNA synthetase encoded by the valanimycin biosynthetic gene cluster

Previous studies have shown that the valanimycin producer Streptomyces viridifaciens contains two genes encoding proteins that are similar to seryl-tRNA synthetases (SerRSs). One of these proteins (SvsR) is presumed to function in protein biosynthesis, because it exhibits a high degree of similarity to the single SerRS of Streptomyces coelicolor. The second protein (VlmL), which exhibits a low similarity to the S. coelicolor SerRS, is hypothesized to play a role in valanimycin biosynthesis, because the vlmL gene resides within the valanimycin biosynthetic gene cluster. To investigate the role of VlmL in valanimycin biosynthesis, VlmL and SvsR have been overproduced in soluble form in Escherichia coli, and the biochemical properties of both proteins have been analyzed and compared. Both proteins were found to catalyze a serine-dependent exchange of 32P-labeled pyrophosphate into ATP and to aminoacylate total E. coli tRNA with L-serine. Kinetic parameters for the two enzymes show that SvsR is catalytically more efficient than VlmL. The results of these experiments suggest that the role of VlmL in valanimycin biosynthesis is to produce seryl-tRNA, which is then utilized for a subsequent step in the biosynthetic pathway. Orthologs of VlmL were identified in two other actinomycetes species that also contain orthologs of the S. coelicolor SerRS. The significance of these findings is herein discussed.     

Characterization of a nonspecific phosphopantetheinyl transferase from Pseudomonas syringae pv. syringae FF5

The 4'-phosphopantetheinyl transferases (PPTases) catalyze the transfer of a 4'-phosphopantetheine moiety from coenzyme A to phosphopantetheine-dependent carrier proteins. The carrier proteins (CPs) are required for the biosynthesis of peptides synthesized by nonribosomal peptide synthases and the biosynthesis of fatty acids and polyketides. A single PPTase (PcpS) is present in the pathogenic bacterium Pseudomonas aeruginosa. Several pathovars of Pseudomonas syringae produce the chlorosis-inducing phytotoxin coronatine. Structural genes for coronatine biosynthesis include two ACPs, two ACP domains, and one peptidyl carrier protein (PCP) domain. To gain insight into factors affecting coronatine biosynthesis, the PPTase of P. syringae pv. syringae FF5 has been investigated. A single PPTase gene (pspT) was amplified from this organism by PCR. The translation product PspT exhibited 62% identity to PcpS as well as higher levels of identity to other, uncharacterized Pseudomonad PPTases. PspT was overproduced in soluble form in Escherichia coli and its enzymatic properties were compared with those of PcpS. PspT exhibited broad substrate specificity, and it displayed the highest activity with a PCP domain. In contrast, the most efficient substrates for PcpS are CPs from primary metabolism. These results indicate phosphopantetheinyl transferases from different Pseudomonas sp. may vary significantly in their enzymatic properties.