Serum Response Factor Contributes Selectively to Lymphocyte Development

Anne Fleige,Siegfried Alberti,Lothar Groöbe,Ursula Frischmann,Robert Geffers,Werner Muöller,Alfred Nordheim,Angela Schippers

doi:10.1074/jbc.m703119200

Abstract

Serum response factor (SRF), is a crucial transcription factor for murine embryonic development and for the function of muscle cells and neurons. Gene expression data show that SRF and its transcriptional cofactors are also expressed in lymphocyte precursors and mature lymphocytes. However, the role of SRF in lymphocyte development has not been addressed in vivo so far, attributed in part to early embryonic lethality of conventional Srf-null mice. To determine the in vivo role of SRF in developing lymphocytes, we specifically inactivated the murine Srf gene during T or B cell development using lymphocyte-specific Cre transgenic mouse lines. T cell-specific Srf deletion led to a severe block in thymocyte development at the transition from CD4/CD8 double to single positive stage. The few residual T cells detectable in the periphery retained at least one functional Srf allele, thereby demonstrating the importance of SRF in T cell development. In contrast, deletion of Srf in developing B cells did not interfere with the growth and survival of B cells in general, yet led to a complete loss of marginal zone B cells and a marked reduction of the CD5+ B cell subset. Our study also revealed a contribution of SRF to the expression of the surface molecules IgM, CD19, and the chemokine receptor 4 in B lymphocytes. We conclude that SRF fulfills essential and distinct functions in the differentiation of different types of lymphocytes.

Highlights

Serum response factor (SRF)2 [1] is a widely expressed transcription factor belonging to an ancient family of DNA-binding
Our study revealed a contribution of SRF to the expression of the surface molecules IgM, CD19, and the chemokine receptor 4 in B lymphocytes
SRF interacts directly with at least two classes of signal-regulated cofactors, the ternary complex factor (TCF) subfamily of Ets domain proteins (SAP-1, Elk-1, and Net) which respond to mitogen-activated protein kinase (MAPK) signaling [3] and members of the myocardin-related transcription factor (MRTF) family (4 – 6), which may be regulated through Rho GTPase/actin signaling

Summary

EXPERIMENTAL PROCEDURES

Lymphocyte Specific Deletion of Srf in Mice—Animals were bred at the Helmholtz Centre for Infection Research under specific pathogen-free conditions and all animal experiments were performed in accordance with institutional guidelines. A T cell-specific anti-CD3 antibody showed a striking decrease of CD3-positive cells, as compared with control specimen (Fig. 1A) This was verified by FACS analysis, which showed decreased numbers of peripheral T cells in spleen, blood, and lymph nodes of CD4-. To address this question we sorted T and B cells from scaled to a target intensity of 150, otherwise using the default thymus and spleen and performed Southern blot analysis to values of the Microarray Suite. Consistent with the absence of CD4 promoter increase or decrease of 1.5, the statistical parameter for a signif- activity in B cells, only the Srf fl, but not the deleted Srf lx allele icant change was less than 0.001 or greater than 0.999, and the could be detected in B cells from spleens of CD4-CreSrf fl/fl signal difference of a certain gene was greater than 40. The Srf fl allele was completely recombined to Srf lx in CD4ϩCD8ϩ DP cells from

RESULTS

B Cell-specific Srf Deletion Leads to a Decrease in B Cell