Four A-10 embryonic rat thoracic aorta myoblasts form a thin sheet across the field of view during the high speed playback of this time-lapse sequence. The cells appear to have formed relatively stable connections between each other and with the substratum. Similar to most other cells in culture, the in vitro behavior of the myoblasts reflects their normal activity in the vertebrate body. Myoblasts are the precursor cells of multinucleated myotubes, the building blocks of muscle tissue. Upon their differentiation in the body, myoblasts adhere to one another and fuse to form myotubes. This process can occur in culture as well, though some myoblast cell lines will continue to divide indefinitely, rather than differentiating, when they are cultured in the presence of fibroblast growth factor.

The two times that a parent cell undergoes mitosis in the video, tiny segments of cytoplasm are left behind when the myoblast rapidly retracts its surface extensions in preparation for the process. The debris can be found at sites of former focal adhesions, regions along the cell surface that are anchored to the substratum via actin-rich stress fibers. Numerous stress fibers, the attachments of which are mediated by transmembrane proteins, can be observed in the myoblasts. The contractile structures also contain myosin and appear as long striations in the flattened lamellipodia of the cells.

Following cell division, the new daughter cells settle upon the surface of the imaging chamber by extending out broad lamellipodia. As the skirt-like protrusions and small, narrower filopodia pass over the sites of former focal adhesions held between the parent cell and the substratum, some of the cell debris becomes incorporated into the daughter cells. The rapidly advancing surface extensions seem to actively seek the exiled material, perhaps due to information obtained by the wildly branching filopodia, which can serve as feelers for animal cells as well as functioning in locomotion.