Multiple roles of the actin and microtubule-regulating formins in the developing brain.

Dynamic control of the actin and microtubule cytoskeletons underlie nearly every critical process during neural development, and requires multiple dimensions of regulation. Formins are a family of fifteen proteins that functions as a major class of linear actin nucleators and regulates both actin and microtubule dynamics. The fact that several closely-related formins show complementary expression patterns during neural development and non-overlapping cytoskeletal functions indicates the need to identify the specialized cellular activities of individual formin members in different neural cell subtypes. In this review, we briefly introduce the known biochemical and regulatory functions of formins in the context of neural development, and summarize their cellular functions in the developing brain.

Dendritic Self-Avoidance and Morphological Development of Cerebellar Purkinje Cells.

Cerebellar Purkinje cells arborize unique dendrites that exhibit a planar, fan shape. The dendritic branches fill the space of their receptive field with little overlap. This dendritic arrangement is well-suited to form numerous synapses with the afferent parallel fibers of the cerebellar granule cells in a non-redundant manner. Purkinje cell dendritic arbor morphology is achieved by a combination of dynamic local branch growth behaviors, including elongation, branching, and retraction. Impacting these behaviors, the self-avoidance of each branch terminal is essential to form the non-overlapping dendritic configuration. This review outlines recent advances in our understanding of the cellular and molecular mechanisms of dendrite formation during cerebellar Purkinje cell development.

MTSS1 Regulation of Actin-Nucleating Formin DAAM1 in Dendritic Filopodia Determines Final Dendritic Configuration of Purkinje Cells.

Dendritic filopodia of developing neurons function as environmental sensors, regulating the spatial organization of dendrites and proper targeting to presynaptic partners. Dendritic filopodia morphology is determined by the balance of F-actin assembled via two major nucleating pathways, the ARP2/3 complex and formins. The inverse-BAR protein MTSS1 is highly expressed in Purkinje cells (PCs) and has been shown to upregulate ARP2/3 activity. PCs in MTSS1 conditional knockout mice showed dendrite hypoplasia due to excessive contact-induced retraction during development. This phenotype was concomitant with elongated dendritic filopodia and was phenocopied by overactivation of the actin nucleator formin DAAM1 localized in the tips of PC dendritic protrusions. Cell biology assays including single-molecule speckle microscopy demonstrated that MTSS1's C terminus binds to DAAM1 and paused DAAM1-mediated F-actin polymerization. Thus, MTSS1 plays a dual role as a formin inhibitor and ARP2/3 activator in dendritic filopodia, determining final neuronal morphology.

Surface chemistry for cytosolic gene delivery and photothermal transgene expression by gold nanorods.

Light-inducible gene regulation has great potential for remote and noninvasive control of the fate and function of target cells. One method to achieve such control is delivery of heat shock protein (HSP) promoter-driven protein expression vectors and photothermal heaters into the cells, followed by activation by illumination. In this study, we show that gold nanorods (AuNRs) functionalized with two conventional lipids, oleate and 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP), are capable of efficient transfection and quick photoactivation of the HSP promoter. Use of our AuNRs (DOTAP-AuNRs) was comparable to Lipofectamine 2000 in terms of transfection efficiency, while lower in cytotoxicity. Subsequent near-infrared laser (NIR) illumination of the cells transfected by DOTAP-AuNRs for 10 s induced time- and site-specific transgene expression without significant phototoxicity, to a degree similar to that of heating the entire culture dish for 30 min. Our mechanistic studies suggest that efficient transfection and quick photoactivation of the HSP promoter (HSP70b') are due to the promoted endosomal escape of DOTAP-AuNRs. We propose a novel protocol for NIR-inducible, site-directed gene expression using an unprecedented complex of the three conventional components capable of both transfection and photothermal heating.