Abstract
Dynamic changes in neuronal morphology and transcriptional regulation play crucial roles in the neuronal network and function. Accumulating evidence suggests that the megakaryoblastic leukemia (MKL) family members, which function not only as actin-binding proteins but also as serum response factor (SRF) transcriptional coactivators, regulate neuronal morphology. However, the extracellular ligands and signaling pathways, which activate MKL-mediated morphological changes in neurons, remain unresolved. Here, we demonstrate that in addition to MKL1, MKL2, highly enriched in the forebrain, strongly contributes to the dendritic complexity, and this process is triggered by stimulation with activin, a member of the transforming growth factor β (TGF-β) superfamily. Activin promoted dendritic complexity in a SRF- and MKL-dependent manner without drastically affecting MKL localization and protein levels. In contrast, activin promoted the nuclear export of suppressor of cancer cell invasion (SCAI), which is a corepressor for SRF and MKL. Furthermore, overexpression of SCAI blocked activin-induced SRF transcriptional responses and dendritic complexity. Collectively, these results strongly suggest that activin-SCAI-MKL signaling is a novel pathway that regulates the dendritic morphology of rat cortical neurons by excluding SCAI from the nucleus and activating MKL/SRF-mediated gene expression.
Highlights
Serum response factor (SRF)4 is a transcription factor that binds to a consensus sequence CC(A/T)6GG
Quantitative PCR analysis with cDNA derived from several tissues revealed that, unlike the broad distribution of MKL1 mRNA, MKL2 plasm (Fig. 7A)
SCAI protein was endogenously expressed that MKL2 is selectively expressed in several forebrain areas in cortical neurons
Summary
Reagents, Plasmids, and Antibodies—These materials are described in the supplemental Experimental Procedures. Dependent cytoskeletal genes or Smad3-dependent genes via In Situ Hybridization—In situ hybridization was performed nuclear translocation of MKL This process may be involved as described previously [28]. To control for the specificity of the hybridization Western Blotting—Protein extracts from NIH3T3 cells, corsignal, parallel experiments were performed in the pres- tical neurons, and brain tissues were prepared according to the ence of a 50-fold excess of an unlabeled oligonucleotide probe. Cytoplaswas performed in an ABI PRISM 7700 sequence detection sys- mic and nuclear extracts of cortical neurons were prepared as tem (Applied Biosystems) using the SYBR Green PCR master described previously [32, 33]. After cells were exposed to the trans- plasmids are described in the supplemental Experimental fection reagents for 4 h, the transfection medium was replaced Procedures. To check the effect of MKL2 on neuronal morphology, an MKL2-expressing construct was cotransfected with a green fluores-
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
