Beyond Chondrocytes: Progenitor-like Cells Drive Cartilage Development in the Quail Embryo Model.

Cartilage regeneration remains a significant challenge due to the tissue's avascular nature and limited chondrocyte regenerative capacity. While mesenchymal stromal cells (MSCs) offer therapeutic promise, their specific role in cartilage remains undefined. This study characterized mesenchymal-like cells in quail embryo cartilage using histochemical staining, immunohistochemistry, and transmission electron microscopy (TEM). A unique population of cartilage-resident progenitor-like cells with flattened, migratory morphologies was identified. These cells co-expressed stemness markers (CD117, CD34), vascularization (VEGF), remodeling (MMP-9), phagocytosis (CD68), and the chondrogenic marker type II collagen. TEM revealed abundant rough endoplasmic reticulum and lysosomes, confirming active metabolic states. Quantitative analysis showed significant differences in marker expression, with CD34 showing the highest expression (p < 0.05). While these findings demonstrate a multifunctional profile, the study remains primarily descriptive and observational. It provides a foundation for future functional investigations and suggests a previously underappreciated role for this progenitor population, offering a mechanistic basis for advancing MSC-based cartilage regeneration therapies.