The CV-1 cell line was initiated in the 1960s from African green monkey (Cercopithecus aethiops) kidney tissue. Since that time, several other lines have been developed from the popular fibroblast line. The COS-7 line was established by Yakov Gluzman in the early 1980s by transformation of the normal CV-1 cells with an origin defective mutant of simian virus 40 (SV40) that codes for the wild-type virus T-antigen. COS-7 cells are commonly utilized by researchers, especially for transfection experiments with recombinant plasmids. The cells grow adherently to both glass and plastic culture dishes.

SV40 is a small DNA tumor virus with a genome that can be readily manipulated by scientists because of its simplicity. The capsid of SV40 is spherical and has such limited space that the genome is only large enough to encode a few functions. Space restraints further require overlapping reading frames for the production of capsid proteins, meaning that the terminal nucleotide sequence of the gene for one protein also serves as the first portion of the gene for another protein. SV40 DNA also encodes the T-antigen protein, which in many primate cells normally controls the replication and packaging of the virus. In some cells, however, T-antigen can bind to p53 and Rb proteins, interfering with their ability to regulate growth and potentially causing tumors to arise in affected tissues.

Filamentous actin and the mitochondrial network were targeted in a culture of transformed African green monkey kidney (COS-7) cells with Alexa Fluor 488 conjugated to phalloidin and MitoTracker Red CMXRos, respectively (illustrated above). DAPI was employed as a nuclear counterstain. Images were recorded in grayscale with a 12-bit digital camera coupled to a Nikon Eclipse 80i microscope equipped with bandpass emission fluorescence filter optical blocks. During the processing stage, individual image channels were pseudocolored with RGB values corresponding to each of the fluorophore emission spectral profiles.