Convergence and extension movements affect dynamic notochord‐somite interactions essential for zebrafish slow muscle morphogenesis

Abstract

During vertebrate gastrulation, convergence and extension (C&E) movements shape and position the somites that form the fast and slow muscles. In zebrafish knypek;trilobite non-canonical Wnt mutants, defective C&E movements cause misshapen somites and reduction of slow muscle precursors, the adaxial cells. Here, we demonstrate essential roles of C&E in slow muscle morphogenesis. During segmentation, the adaxial cells change shapes and migrate laterally to form slow muscles at the myotome surface. Using confocal imaging techniques, we show that the adaxial cells undergo three-step shape changes, including dorsoventral elongation, anterior-ward rotation, and anteroposterior elongation. The adaxial cells in knypek;trilobite double mutants maintain prolonged contact with the notochord and fail to rotate anteriorly. Such a defect was suppressed by physical removal of their notochord or by introducing wildtype notochord cells into the mutant. We propose that in the double mutants, impaired C&E movements disrupt notochord development, which impedes the adaxial cell shape changes. Developmental Dynamics

Extracellular matrix assembly and organization during zebrafish gastrulation

“…By contrast, of the 16-collagen isoforms thus far described in zebrafish, only col15a1 shows appreciable mRNA expression in the early embryo (Thisse et al, 2001;Pagnon-Minot et al, 2008). At the protein level, the earliest embryonic stage FN has been reported is 5 somites (11.5 h) where it was shown to localize at intersomitic regions and to the sheath of ECM adjacent to the notochord (Yin and Solnica-Krezel, 2007). Laminin protein (LN) was also shown to accumulate at somite boundaries during somitogenesis stages (Parsons et al, 2002) and to be enriched adjacent to the notochord at the tailbud stage (10 h) (Crawford et al, 2003).…”

Intracellular Golgi Complex organization reveals tissue specific polarity during zebrafish embryogenesis

“…Several morphologic features of the notochord suggest it may be organized with an apical‐basal epithelial polarity (Rodriguez‐Boulan and Macara, ). Extracellular matrix is deposited on the outside of the notochord and remodeled during gastrulation movements in vertebrates (Yin and Solnica‐Krezel, ; Davidson et al, ; Latimer and Jessen, ; Jessen, ). At early segmentation stages, notochord cells are shaped as flattened wedges partly spanning or disks fully spanning the notochord (Fig.…”

Rbm24a and Rbm24b Are Required for Normal Somitogenesis

“…We additionally evaluated whether observed rbm24a MO and rbm24b MO phenotypes were a consequence of gastrulation defects whose effects we were simply observing later in development [50]. We established if rbm24a and rbm24b are expressed prior to or during gastrulation.…”