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Regulated SMAD signalling in development

ABSTRACT: Phosphorylation and subsequent nuclear translocation of SMAD proteins determine the cellular response to activin. Here we identify a novel means by which activin signalling is regulated to enable developmental stage-specific SMAD gene transcription. In response to activin A, immature proliferating mouse Sertoli cells exhibit nuclear accumulation of SMAD3, but not SMAD2, although both proteins are phosphorylated. In post-mitotic differentiating cells, both SMAD2 and SMAD3 accumulate in the nucleus. Furthermore, immature Sertoli cells are sensitive to activin dosage; at higher concentrations maximal SMAD3 nuclear accumulation is observed, accompanied by a small, but significant, increase in nuclear SMAD2. Microarray analysis confirmed that differential SMAD utilization correlated with altered transcriptional outcomes and identified new activin target genes, Gja1 and Serpina5, which are known to be required for Sertoli cell development and male fertility. In immature Sertoli cells, genetic or transient knockdown of SMAD3 enhanced SMAD2 nuclear accumulation in response to activin, with increased Serpina5 mRNA levels associated with nuclear localized SMAD2. In transgenic mice with altered activin bioactivity that display male fertility phenotypes, testicular Gja1 and Serpina5 mRNA levels reflected altered in vivo activin levels. We conclude that regulated nuclear accumulation of phosphorylated SMAD2 is a novel determinant of developmentally regulated activin signalling.

ORGANISM(S): Mus musculus

PROVIDER: GSE13106 | GEO | 2009/09/09

SECONDARY ACCESSION(S): PRJNA109939

REPOSITORIES: GEO

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Project description:TGF-b is an important pleiotropic cytokine with potent immunoregulatory properties. Although many previous reports have been proposed for the immunoregulatory functions of TGF-b on T cells, such as the suppression of cell proliferation, cytokine production and cytokine signaling, as well as the induction of apoptosis, it is not well elucidated whether the each effect of TGF-b on T cells is dependent on Smad signaling or Smad-independent other signaling pathways. The aim of the study was to clarify the involvement of Smad signaling and to investigate the redundancy of Smad2 and Smad3 on various TGF-b-mediated regulation of gene expression in CD4+ T cells. We used microarrays to detail the global program of gene expression regulated by TGF-b in CD4+ T cells, and identified distinct classes of up/down-regulated genes which are dependent on or independent of TGF-b-Smad signaling. Most of genes regulated by TGF-b were redundantly dependent on Smad2 and Smad3, including Foxp3 and IL-2. In addition, some genes were sufficiently regulated via Smad2 or Smad3 signaling alone. In contrast, TGF-b-mediated RORgt induction was independent of Smad signaling. CD4+CD25-CD44loCD62Lhi T cells (naive) were isolated from the spleens in wild-type (WT), T cell-specific Smad2 conditional knockout (Smad2KO or Smad2del/del), Smad3 knockout (Smad3KO or Smad3-/-) or Smad2del/delSmad3+/- mice by using a BD FACS ariaTM cell sorter (BD Bioscience) (purity: >98%). Freshly purified cells were then stimulated with anti-TCR stimuli in the absence or presence of TGF-b for 24 hr, respectively. A complete and precise experimental procedure is given in the "treatment protocol". It was very difficult to obtain the enough number of CD4+CD25-CD44loCD62Lhi naive T cells from Smad2del/delSmad3-/- mice because alomost all of CD4+ T cells were activated in Smad2del/delSmad3-/- mice. We confirmed that the several known Smad-regulated genes were almost out of control in Smad2del/delSmad3+/- CD4+ T cells by using quantitative RT-PCR. Furthermore, previous studies have reported the similar results in other cell types deficit in two alleles of Smad2 and one allele of Smad3. For these reasons, we substituted Smad2del/delSmad3+/- naive T cells for Smad2/3-deficient naive T cells. Cells were quickly collected 24 hr after culture for RNA extraction and hybridization on Affymetrix microarrays.

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Regulated SMAD signalling in development

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