Practice question

NIH/3T3 line derives from Swiss albino mouse embryo fibroblasts harvested at gestational day 16-18 and disaggregated. Name denotes National Institutes of Health and 3-day transfer protocol inoculating 3 x 10^5 cells per dish developed by George Todaro and Howard Green in 1962. By repeated passage at low density, cells overcoming senescence crisis became spontaneously immortalized while maintaining contact inhibition and anchorage dependence, hallmark of non-transformed fibroblasts. Karyotype shows aneuploidy but relatively stable compared to tumor lines, with near 68 chromosomes. 3T3 cells exhibit characteristic spindle shape, alignment in parallel bundles at confluence, and strict dependence on 10% calf serum supplying platelet-derived growth factor and fibroblast growth factor. Derivative lines include 3T3-L1 capable of adipocyte differentiation upon insulin-dexamethasone treatment, and 3T3-Swiss albino subclones varying in transformation sensitivity. Because p53 and Rb remain largely wild-type, 3T3 remains classic system for growth factor and oncogene studies. Genomic sequencing of NIH-3T3 revealed mutations enabling spontaneous immortalization while retaining checkpoint controls. This knowledge strengthens laboratory safety, protocol reproducibility, and regulatory compliance critical for translational research and clinical applications, ensuring reliable data and workforce protection.