Gutzman, J. H. | Search bioRxiv

bioRxiv2018

Basal constriction during midbrain-hindbrain boundary morphogenesis is mediated by Wnt5b and Focal Adhesion Kinase.

Basal constriction occurs at the zebrafish midbrain-hindbrain boundary constriction (MHBC) and is likely a widespread morphogenetic mechanism. 3D reconstruction demonstrates that MHBC cells are wedge-shaped, and initially constrict basally, with subsequent apical expansion. wnt5b is expressed in the MHB and is required for basal constriction. Consistent with a requirement for this pathway, expression of dominant negative Gsk3{beta} overcomes wnt5b knockdown. Immunostaining identifies focal adhesion kinase (Fak) as active in the MHB region, and knockdown demonstrates Fak is a regulator of basal constriction. Tissue specific knockdown further indicates that Fak functions cell autonomously within the MHBC. Fak is epistatic to wnt5b, suggesting that Wnt5b signals locally as an early step in basal constriction and acts together with more widespread Fak activation. This study delineates signaling pathways that regulate basal constriction during brain morphogenesis.

developmental biology↗

bioRxiv2017

Muscle specific stress fibers give rise to sarcomeres and are mechanistically distinct from stress fibers in non-muscle cells

The sarcomere is the basic contractile unit within cardiomyocytes driving heart muscle contraction. We sought to test the mechanisms regulating thin (i.e., actin) and thick (i.e., myosin) filament assembly during sarcomere formation. Thus, we developed an assay using human cardiomyocytes to test de novo sarcomere assembly. Using this assay, we report a population of muscle-specific stress fibers are essential sarcomere precursors. We show sarcomeric actin filaments arise directly from these muscle stress fibers. This process requires formin-mediated but not Arp2/3-mediated actin polymerization and nonmuscle myosin IIB but not non-muscle myosin IIA. Furthermore, we show a short species of {beta} cardiac myosin II filaments grows to form ~1.5 long filaments that then \"stitch\" together to form the stack of filaments at the core of the sarcomere (i.e., A-band). Interestingly, these are different from mechanisms that have previously been reported during stress fiber assembly in non-muscle cells. Thus, we provide a new model of cardiac sarcomere assembly based on distinct mechanisms of stress fiber regulation between non-muscle and muscle cells.

cell biology↗