COS-1 is a transformed cell line that was developed by Yakov Gluzman from the CV-1 African green monkey kidney fibroblast line, which was established in the mid-1960s. Two other similarly transformed lines, COS-3 and COS-7, were also initiated from the CV-1 line by Gluzman.

The COS-1 cell line was produced via transformation of the previously established line with an origin defective mutant of simian virus 40 (SV40) that codes for wild type large tumor antigen (T antigen). Integrated into COS-1 cells is a copy of the entire early region of the SV40 genome. The cells fully support the lytic growth of SV40 (tsA209 strain) when cultured at 40 degrees Celsius as well as the replication of mutants of SV 40 that exhibit deletions in the early region.

SV40 has been the subject of significant scientific interest over the last few decades and, consequently, COS-1 cells are a popular tool for research. SV40 is known to have been accidentally introduced to large segment of the human population during the mid-twentieth century through tainted polio vaccines produced in the kidney cells of African green monkeys and rhesus monkeys. In certain simian hosts, SV40, which is one of the Papovaviridae family of viruses, infects tissues, reproduces, and then destroys cells as newly produced viruses emerge. Studies have indicated, however, that when the virus invades certain mammalian cells, its reproduction is often hindered, but the virus may produce T-antigen and incite oncogenic transformation in the host. SV40 has been shown to incite tumor growth in rodents and may be linked with the development of mesothelioma and certain other kinds of cancer in humans.

The transformed African green monkey kidney cells presented in the digital image above were resident in an adherent culture immunofluorescently labeled with Alexa Fluor 488 and Alexa Fluor 568 conjugated to goat secondary antibodies that target mouse anti-fibrillarin (nucleoli) and rabbit anti-giantin (targeting the Golgi complex) primary antibodies, respectively. Nuclei were stained with Hoechst 33258. Images were recorded in grayscale with a 12-bit digital camera coupled to either a Nikon E-600 or 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.

Proximity of Mitochondria and Cytoskeletal F-Actin Framework in COS-1 Cells - The intracellular relationship between mitochondria and the filamentous actin network was visualized in a culture of COS-1 fibroblasts with MitoTracker Red CMXRos and Alexa Fluor 488 conjugated to phalloidin. Cell nuclei were counterstained with Hoechst 33342.

Transformed Monkey Kidney Fibroblasts Labeled with Soybean Agglutinin - Presented in this section is an adherent culture of COS-1 fibroblasts that was labeled with Alexa Fluor 488 conjugated to soybean agglutinin, a lectin that binds terminal alpha- and beta-N-acetylgalactosamine and galactopyranosyl residues. In addition, the cells were labeled with Texas Red conjugated to phalloidin and DAPI, targeting the cytoskeletal F-actin network and DNA, respectively.