Expression of activin receptor-like kinase 7 in adipose tissues.

The tissue distribution of activin receptor-like kinase 7 (Alk7) expression, the signaling ability of Alk7 variants, and Alk7 expression in response to ß3-adrenergic receptor activation were examined. Expression levels of Alk7 varied greatly among tissues but were highest in white adipose tissue and brown adipose tissue. In addition to full-length Alk7 (Alk7-v1), Alk7-v3, an Alk7 variant, was expressed in adipose tissues, brain, and ovary. Nodal transmits signals via Alk7 in cooperation with its coreceptor, Cripto. Evaluation of the ability of Alk7 variants to confer Nodal signaling using luciferase-based reporter assays showed that Alk7-v3 does not transmit Nodal-Cripto-mediated signals. Expression of Alk7 was down-regulated in brown but not in white adipose tissue treated with CL316,243, a ß3-adrenergic receptor agonist. These results suggest involvement of Alk7 in modulation of metabolism in the adipose tissues in response to ß3-adrenergic receptor activation.

Microphthalmia-associated transcription factor is required for mature myotube formation.

BACKGROUND: The roles of microphthalmia-associated transcription factor (Mitf) in the skeletal muscle and during myogenesis are unclear. METHODS: Expression of Mitf in mouse tissues and during myogenesis was evaluated. Effects of Mitf knockdown on myogenesis and gene expression related to myogenesis were subsequently explored. Furthermore, effects of p21, a cyclin-dependent kinase inhibitor, and integrin α9 (Itga9) were examined. RESULTS: Mitf was highly expressed in the skeletal muscle; Mitf-A and -J were expressed. Mitf expression increased after differentiation stimulation in C2C12 myogenic cells. Down-regulation of Mitf expression by transfection of siRNA for common Mitf inhibited myotube formation, which was reproduced by Mitf-A knockdown. Morphometric analyses indicated that both multinucleated cell number and the proportion of myotubes with more than 6 nuclei were decreased in Mitf-knockdown cells, suggesting that Mitf is required for not only the formation of nascent myotubes but also their maturation. Searching for genes positively regulated by Mitf revealed p21 and Itga9; decreasing Mitf expression inhibited up-regulation of p21 expression after differentiation stimulation and blocked the induction of Itga9 expression in response to differentiation. Knockdown of p21 decreased the number of multinucleated cells, whereas Itga9 knockdown did not affect the myotube number. Both p21 knockdown and Itga9 knockdown decreased the proportion of myotubes with more than 6 nuclei. GENERAL SIGNIFICANCE: Mitf positively regulates skeletal muscle formation; Mitf is significantly expressed during myogenesis, and is required for efficient myotube formation through expression of p21 and Itga9.

Nucleotide sequence of canine Smad3.

The whole genome sequence of a Boxer dog suggested that the amino acid sequence of the carboxyl terminus of a putative Smad3 is SSVF-(COOH), not SSVS-(COOH) as in all Smad3 sequences identified in many species. Because phosphorylation of the last two serines at the carboxyl terminus is generally indispensable for Smad3-mediated signaling, the role of Smad3 may be unique in dogs. The present study determines the nucleotide sequence of the coding region of canine Smad3 and deduces the carboxyl terminal amino acids of Smad3 in several breeds. Except for the Boxer, the deduced amino acid sequence was SSVS-(COOH) in all dogs examined. In addition, the nucleotide at position 1204 in the Boxer was different from that of the other dogs. Furthermore, there was a SNP at nt 240. The present study indicates that the carboxyl terminal amino acid of canine Smad3 is not unique, although it is unknown in the Boxer breed.

A JNK inhibitor SP600125 induces defective cytokinesis and enlargement in P19 embryonal carcinoma cells.

While analyzing the role of c-Jun NH(2)-terminal kinase (JNK) in neurogenesis in P19 embryonal carcinoma cells, we noticed that treatment with SP600125, a JNK inhibitor, increased the cell size markedly. SP600125-induced enlargement of P19 cells was time- and dose-dependent. The increased cell size in response to SP600125 was also detected in B6mt-1 embryonic stem cells. SP600125 treatment inhibited cell growth and increased DNA contents, indicating the inhibition of cell proliferation resulting from endoreduplication. Concurrently, the gene expression of p21, a regulator of G2/M arrest as well as G1 arrest, was increased in cells treated with SP600125. The increased cell size in response to SP600125 was detected even in P19 cells treated with colcemide, an inhibitor of cell cycle progression at the metaphase. The present study suggests that treatment with SP600125 progresses the cell cycle, skipping cytokinesis in P19 cells.

Gene expression of the TGF-beta family in rat brain infected with Borna disease virus.

CRNP5, a variant of Borna disease virus (BDV), has stronger pathogenesis in rats than the related variant CRP3, although only 4 amino acids in the whole genome are different. As a first step to clarify the differential pathogenesis between the variants, the present study focused on examining the expression of the transforming growth factor (TGF)-beta family in the brain of rats infected with BDV. The main results were as follows. (1) BDV infection, irrespective of the variant, up-regulates TGF-beta1 expression in the brain, (2) the expressions of signal receptors for TGF-beta1 are also increased, (3) the expression of brain inhibin/activin betaE is up-regulated by BDV infection, and (4) the expression of brain inhibin/activin betaC tends to be higher in rats exhibiting severe Borna disease. These results indicate that members of the TGF-beta family are involved in neuronal disorders induced by BDV infection in a ligand-dependent manner. In particular, up-regulation of inhibin/activin betaC may be a key event responsible for induction of the stronger pathogenesis of the CRNP5 variant of BDV.