Fine-tuned SRF activity controls asymmetrical neuronal outgrowth: implications for cortical migration, neural tissue lamination and circuit assembly

Abstract

The stimulus-regulated transcription factor Serum Response Factor (SRF) plays an important role in diverse neurodevelopmental processes related to structural plasticity and motile functions, although its precise mechanism of action has not yet been established. To further define the role of SRF in neural development and distinguish between cell-autonomous and non cell-autonomous effects, we bidirectionally manipulated SRF activity through gene transduction assays that allow the visualization of individual neurons and their comparison with neighboring control cells. In vitro assays showed that SRF promotes survival and filopodia formation and is required for normal asymmetric neurite outgrowth, indicating that its activation favors dendrite enlargement versus branching. In turn, in vivo experiments demonstrated that SRF-dependent regulation of neuronal morphology has important consequences in the developing cortex and retina, affecting neuronal migration, dendritic and axonal arborization and cell positioning in these laminated tissues. Overall, our results show that the controlled and timely activation of SRF is essential for the coordinated growth of neuronal processes, suggesting that this event regulates the switch between neuronal growth and branching during developmental processes.

SRF and SRFΔ5 Splicing Isoform Recruit Corepressor LSD1/KDM1A Modifying Structural Neuroplasticity and Environmental Stress Response

“…These results indicate that in resting conditions both SRF and SRFD5 act as negative modifiers of spines-related structural plasticity. This result only apparently contrasts previous data scoring SRF as a positive regulator of spine density [46]. Indeed, to our knowledge, we are the first to overexpress full length SRF in neurons to evaluate spine density in basal conditions.…”

“…SRF is known to represent a master regulator of neuronal structural plasticity by virtue of its ability to guide a transcriptional program of gene expression aimed at regulating actin dynamics [17,45,46]. To assess neuroplastic implications of SRFD5 in primary hippocampal neurons we overexpressed recombinant myc-tagged SRF and SRFD5 vectors along with GFP, and analyzed neurites arborization at day in vitro 8 (DIV8) during in vitro maturation, and spine density in more mature neurons at DIV18 using confocal microscopy.…”

“…Indeed, to our knowledge, we are the first to overexpress full length SRF in neurons to evaluate spine density in basal conditions. Every other work describing SRF as a positive spine regulator either used overexpression of a constitutively active SRF (gain-of-function generated by fusing SRF with potent VP16 transactivation domain) [46,47], or performed the experiments upon conditions of neuronal activation [48].…”

Translating intracarotid artery transplantation of bone marrow-derived NCS-01 cells for ischemic stroke: Behavioral and histological readouts and mechanistic insights into stem cell therapy

“…Similarly, overexpression of transmembrane glycoprotein CD44 in vitro promotes the elongation, spread, and number of filopodia of cultured neural precursor cells, while in vivo accelerates the transendothelial migration and facilitates the invasion of certain perivascular sites . Filopodia formation and cell motility, especially transendothelial migration, may be facilitated by adhesion molecules, such as Ninjurin 1, and transcription factors, including serum response factor . Understanding the putative role of these transmembrane glycoproteins, adhesion molecules, and regulatory factors may improve filopodia formation, as well as the resulting therapeutic outcome of NCS‐01 cells in stroke.…”

“…45 Filopodia formation and cell motility, especially transendothelial migration, may be facilitated by adhesion molecules, such as Ninjurin 1, 46 and transcription factors, including serum response factor. 47 Understanding the putative role of these transmembrane glycoproteins, adhesion molecules, and regulatory factors may improve filopodia formation, as well as the resulting therapeutic outcome of NCS-01 cells in stroke.…”