C57BL/6 mice, often referred to as “black six” or “B6,” are the most widely used inbred strain in biomedical research. They are routinely employed across various disciplines, contributing to our understanding of human health and disease. Their consistent use has solidified their place as a standard model in laboratories globally.
What Makes C57BL/6 Mice Unique
C57BL/6 mice have distinct characteristics valuable for scientific investigation. They are easily recognizable by their dark brown, almost black, glossy coats. Beyond their appearance, these mice exhibit specific behavioral patterns, such as being more sensitive to noise and odors compared to other laboratory strains, and they may be more prone to biting than more docile strains like BALB/c.
Physiologically, C57BL/6 mice have several predispositions relevant to human health. They show a notable susceptibility to diet-induced obesity, type 2 diabetes, and atherosclerosis, especially when fed high-fat diets. These mice are also prone to age-related hearing loss, which begins at high frequencies and progresses over time, making them a model for this common human condition. They also have a high preference for alcohol, making them suitable for studies on alcoholism and addiction.
Why C57BL/6 Mice Are Essential for Science
The widespread use of C57BL/6 mice in research stems from their remarkable genetic homogeneity. As an inbred strain, C57BL/6 mice are nearly genetically identical. This genetic uniformity enables scientific reproducibility, minimizing variability that could otherwise confound experimental results across studies and laboratories.
Their robust nature and ease of breeding further contribute to their status as a standard research model. C57BL/6 mice have a median lifespan of 27–29 months, with a maximum lifespan around 36 months, providing a sufficient window for long-term studies. Their ready availability from commercial suppliers worldwide simplifies access for researchers, allowing for standardized research models to be implemented broadly. This combination of genetic consistency, hardiness, and accessibility makes them a valuable resource for generating reliable and comparable data in biomedical investigations.
Major Research Applications
C57BL/6 mice are used across many scientific disciplines due to their biological characteristics. In immunology, they are employed to study immune responses, including cell-mediated immunity and Natural Killer (NK) cell activity, which is relatively high in this strain. This makes them valuable for vaccine development and understanding autoimmune diseases.
In cancer research, C57BL/6 mice serve as models for tumor development and testing new therapies. While they have a low natural incidence of certain cancers, they are a common genetic background for creating genetically modified mice that model various human cancers, allowing for the study of tumor growth and therapeutic interventions. Their susceptibility to metabolic disorders makes them suitable for investigations into diabetes and obesity, particularly diet-induced models. C57BL/6 mice are also used in neuroscience to study neurodegenerative diseases and various behaviors, including anxiety and depression.
Important Considerations for Researchers
While C57BL/6 mice are widely used, researchers must consider their specific nuances. Different substrains, such as C57BL/6J and C57BL/6N, have accumulated genetic and phenotypic differences since their separation in 1951. These subtle genetic variations can influence experimental outcomes, meaning results from one substrain may not be directly transferable to another without careful consideration.
C57BL/6 mice exhibit specific behavioral patterns, such as “barbering” where dominant males remove hair from cage mates, which could influence behavioral studies. Their heightened sensitivity to pain and cold, and reduced effectiveness of some pain medications, requires careful attention in experimental design. Their unique genetic background means that findings from C57BL/6 mice may not always be universally applicable to all other mouse strains or humans without further validation. Researchers should also be mindful of environmental factors, like noise and odors, and the mouse’s microbiome, as these can impact study results.