Expression and function of Ebf1 gene during chondrogenesis in chick embryo limb buds

The expression profile of early B-cell factor (Ebf) genes and loss of function experiments denote a crucial role for these genes during the late stage of skeletogenesis. However, little is known regarding the expression and function of these genes during the early stage of skeletogenesis. Therefore, this study aimed to detail the spatiotemporal expression pattern of cEbf1, in comparison to cEbf2 and cEbf3, in chick limb buds and investigate its function during chondrogenesis. cEbf1-3 were co-expressed in the distal mesenchyme from a very early stage and later in the outer perichondrium and the surrounding noncartilaginous mesenchymal cells. Ebf1 loss of function through injection of RCASBP virus-carrying Ebf1 dominant-negative form (ΔEbf1) into the wing buds resulted in shortened skeletal elements with a clear defect in the chondrocyte differentiation program. In RCASBP-ΔEbf1 injected wing, the chondrogenesis was initiated normally but hindered at the maturation stage. Subsequently, the chondrocytes failed to become mature or hypertrophic and the long bone diaphysis was not properly developed. The final phenotype included shorter, thicker, and fused long bones. These phenotypic changes were associated with downregulation of the early [Sox9 and collagen type II (Col2a1)] and the late [alkaline phosphatase (AP)] chondrocytes differentiation markers in the limb buds. These results conclude that cEbf1 could be involved in a molecular cascade that promotes the terminal stages of chondrogenesis in the long bone anlagen.