Pectoral Fin Anomalies in Knockdown Zebrafish Embryos Related to the Cascade Effect of N-Cadherin and Extracellular Matrix Formation.

Functional knockdown of zebrafish causes hypoplasia or aplasia of pectoral fins. This study aimed to assess developmental pectoral fin anomalies in morpholino knockdown zebrafish embryos. The expression of cartilage-related genes in the morphant was analyzed by DNA microarray, immunostaining, and thin-section histology to examine the detailed distribution of the extracellular matrix (ECM) during different pectoral fin developmental stages. Chondrogenic condensation (CC) in the morpholino knockdown group was barely recognizable at 37 h postfertilization (hpf); the process from CC to endoskeleton formation was disrupted at 48 hpf, and the endoskeleton was only loosely formed at 72 hpf. Microarrays identified 18 downregulated genes in -deficient embryos, including 2 fin morphogenesis-related (, ), 4 fin development-related (, , , ), and 12 cartilage development-related (, , , , , , , , , , , , ) genes, at 24 and 30 hpf. The increase in apoptosis-related proteins (BAD and BCL2) in the morphant influenced the cellular component of pectoral fins and resulted in chondrocyte reduction throughout the different CC phases. Furthermore, knockdown interfered with ECM formation in pectoral fins, affecting glycosaminoglycans, fibronectin, hyaluronic acid (HA), and N-cadherin. Our results provide evidence that the pectoral fin phenotypic anomaly induced by knockdown is related to disruption of the mesoderm and ECM, consequently interfering with mesoderm migration, CC, and subsequent endoskeleton formation.