Microfilaments were visualized in the human bone osteosarcoma cells featured in the digital video sequences in this section with mCherry fused to Lifeact. Also known as actin filaments, microfilaments are usually nucleated at the plasma membrane, unlike microtubules, which typically extend from centrosomes. Thus the cell periphery is generally the cellular region containing the highest concentration of microfilaments. A variety of external factors, however, and a collection of specialized proteins strongly influence the characteristics of microfilaments. C-Src was also targeted in the featured cells with mCherry, one of the red members of the "mFruit" family of fluorescent proteins.