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Cellular localization and dendritic function of rat isoforms of the SRF coactivator MKL1 in cortical neurons

Mitsuru Ishikawa1, Jun Shiota, Yuta Ishibashi

  • 1aLaboratory of Molecular Neurobiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama bDepartment of Neurobiology and Behavior, Gunma University, Graduate School of Medicine, Maebashi cDivision of Pharmacology, Biological Safety Research Center, National Institute of Health Sciences, Tokyo, Japan dSolomon H. Snyder Department of Neuroscience, Johns Hopkins University, School of Medicine, Baltimore, Maryland, USA.

Neuroreport
|March 5, 2014
PubMed

Insights

The number of actin-binding motifs in megakaryoblastic leukemia 1 (MKL1) isoforms influences their nuclear entry and regulation of serum response factor (SRF) gene expression, impacting dendritic morphology.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Neuroscience

Background:

  • Megakaryoblastic leukemia 1 (MKL1) acts as a serum response factor (SRF) coactivator, regulated by G-actin binding via RPEL motifs.
  • MKL1 localization shifts from cytoplasm to nucleus upon dissociation from G-actin, activating SRF-mediated gene expression.
  • Several MKL1 isoforms exist, differing in RPEL motif number and potentially function.

Purpose of the Study:

  • To investigate how different MKL1 isoforms, varying in RPEL motif count, affect subcellular localization, transcriptional activity, and neuronal morphology.
  • To determine if the number of RPEL motifs dictates MKL1 isoform function in SRF-mediated gene expression and neuronal development.

Main Methods:

  • Cultured cortical neurons were transfected with FLAG-tagged MKL1 isoforms.
  • Immunofluorescent staining was used to assess subcellular localization of MKL1 isoforms.
  • SRF-mediated transcriptional activity and neuronal morphology (dendritic number, axonal length) were quantified after isoform overexpression.

Main Results:

  • All MKL1 isoforms localized to both cytoplasm and nucleus, with MKL1met (2 RPEL motifs) showing enhanced nuclear presence compared to isoforms with 3 RPEL motifs.
  • Overexpression of MKL1met, but not other isoforms, significantly increased SRF-mediated transcription and reduced dendritic number.
  • Axonal length remained unaffected by any MKL1 isoform overexpression.

Conclusions:

  • The number of RPEL motifs in MKL1 isoforms regulates their subcellular localization, influencing SRF-mediated gene expression.
  • MKL1 isoform localization dictates their impact on dendritic morphology, with MKL1met inhibiting dendritic growth.
  • These findings highlight the role of actin-binding motifs in MKL1 function and neuronal development.

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