Avian Serum Response Factor Expression Restricted Primarily to Muscle Cell Lineages Is Required for α-Actin Gene Transcription

Abstract

Serum response factor (SRF) gene expression in avian embryonic muscle lineages plays a central role in activating alpha-actin gene activity. In early stage HH 6 avian embryos, SRF mRNA expression showed strong localization to the neural groove, primitive streak, lateral plate mesoderm, and Hensen's node, while distinct SRF expression was seen later in the neural folds and the somites by HH stage 8. SRF transcripts appeared in the precardiac splanchnic mesoderm in stage HH 9 embryos and was detected at higher levels in the myocardium, somites, and lateral mesoderm of HH 11 embryos. SRF antibody staining demonstrated significant SRF protein accumulation in the myocardium of the developing heart and the myotomal portion of somites. During primary myogenesis in culture, SRF transcripts and nuclear SRF protein content increased about 40-fold, as primary myoblasts withdrew from the cell cycle, reaching their highest levels prior to the upregulation of the skeletal alpha-actin gene. A dominant-negative SRF mutant, SRFpm1, which inhibited DNA binding, but not dimerization of monomeric SRF subunits, blocked transcriptional activation of a skeletal alpha-actin promoter-luciferase reporter gene during myogenesis. Transcriptional blockade was reversed by co-transfections of a wild-type SRF expression vector, but was not rescued by the expression of other myogenic factors, such as MyoD and Mef-2C. Thus, SRF displayed an embryonic expression pattern restricted primarily to striated muscle cell lineages, in which increased mass of nuclear SRF was obligatory for alpha-actin gene transcription.

Stem cells and the formation of the myocardium in the vertebrate embryo

“…During these latter stages, a large number of transcription factors become expressed in the cardiogenic mesoderm in a pattern that demarcates this merging tissue. Among the genes expressed in the early cardiogenic mesoderm of the vertebrate embryo are Nkx.2.5, Nkx.2.6, Nkx.2.8, GATA4, GATA5, GATA6, Tbx2, Tbx3, Tbx5, MEF2a, MEF2c, serum response factor (SRF), the homeodomain molecule HOP, and the histone deacetylase-dependent transcriptional repressor Bop (Edmondson et al, 1994;Schultheiss et al, 1995;Croissant et al, 1996;Brand et al, 1997;Reecy et al, 1997;Biben et al, 1998;Jiang et al, 1998;Buchberger and Arnold, 1999;Yamada et al, 2000;Chen et al, 2002;Gottlieb et al, 2002;Shin et al, 2002). Two points need to be kept in mind when understanding the function of these molecules for cardiac differentiation.…”

Cell-specific nuclear import of plasmid DNA

“…The human SRF gene was removed from pCGN-SRF 16,35,36 and inserted into the multiple cloning site of pBK-CMV (Stratagene) to create pBK-SRF.…”

Expression of the SRF gene occurs through a Ras/Sp/SRF-mediated-mechanism in response to serum growth signals

“…SRF also regulates transcription mediated by treatment of cells with neurotrophins (Sheng et al, 1988;Visvader et al, 1988), neurotransmitters and agents that raise intracellular calcium levels (Bading et al, 1993;McDonough et al, 1997;Misra et al, 1994), stress agents, and viral activators (Avantaggiati et al, 1993;Fujii et al, 1992Fujii et al, , 1994. A variety of experiments indicate that SRF is a key transcription factor controlling genes that are involved in cell cycle progression, di erentiation, and development (Arsenian et al, 1998;Croissant et al, 1996;Gauthier-Rouviere et al, 1991;Vandromme et al, 1992). Understanding both the mechanism by which SRF mediates the activation of genes and regulation of the SRF gene itself will therefore be important for understanding these processes.…”