High Confluency Induced Differentiation of C2C12 Myoblasts into Myotubes in Plain DMEM Without Horse Serum

The murine C2C12 myoblast cell line is widely used to study skeletal muscle differentiation, regeneration, and disease. Standard protocols induce differentiation by replacing growth medium with low-serum medium containing 2% horse serum (HS). However, HS introduces biological variability, reduces reproducibility, and raises costs, limiting its utility for applications requiring chemically defined conditions. Here, we present a simplified, cost-effective method for inducing C2C12 differentiation without serum or commercial supplements. We show that when C2C12 cultures reach high confluence (≥ 95%), continued incubation in plain DMEM, without HS or additives, efficiently drives myogenic differentiation. Phase contrast microscopy revealed hallmark morphological changes such as elongation, alignment, and multinucleation. Fusion index analysis confirmed that differentiation levels matched those achieved with traditional HS protocols. This method requires only basic culture conditions and imaging, making it accessible to laboratories lacking advanced microscopy or staining resources. By eliminating serum, the protocol reduces experimental noise and provides a clearer view of intrinsic regulatory mechanisms driving myogenesis. Our findings highlight the endogenous capacity of high-density C2C12 cultures to differentiate without exogenous cues, offering a practical, reproducible alternative to serum-based protocols for muscle research, tissue engineering, and studies of cell-density–dependent signalling.