Attention to Background Strain Is Essential for Metabolic Research: C57BL/6 and the International Knockout Mouse Consortium

Abstract

The International Knockout Mouse Consortium (IKMC) introduces its targeted constructs into C57BL/6N embryonic stem cells. However, breeding with a Cre-recombinase and/or Flp-recombinase mouse is required for the generation of a null allele with the IKMC cassette. Many recombinase strains are in the C57BL/6J background, resulting in knockout animals on a mixed strain background. This can lead to variability in metabolic data and the use of improper control groups. While C57BL/6N and C57BL/6J are derived from the same parental C57BL/6 strain, there are key genotypic and phenotypic differences between these substrains. Many researchers may not even be aware of these differences, as the shorthand C57BL/6 is often used to describe both substrains. We found that 58% of articles involving genetically modified mouse models did not completely address background strain. This review will describe these two substrains and highlight the importance of separate consideration in mouse model development. Our aim is to increase awareness of this issue in the diabetes research community and to provide practical strategies to enable researchers to avoid mixed strain animals when using IKMC knockout mice.

Microglia mediate postoperative hippocampal inflammation and cognitive decline in mice

“…LCR rats do not adequately resolve postoperative inflammation and develop cognitive decline that persists for months (37). We now show that LXA 4 levels do not rise appropriately following aseptic trauma in C57BL/6 mice with DIO, which also have reduced glycemic control and other features of metabolic syndrome (38). This finding indicates that, like LCR rats, mice with DIO fail to properly resolve postoperative inflammation.…”

A Direct Comparison of Metabolic Responses to High-Fat Diet in C57BL/6J and C57BL/6NJ Mice

“…Hyperinsulinemia was the most notable of these markers, as 6J mice appear relatively resistant to elevations in blood insulin over the course of a short-term HFD. These findings highlight the overt differences between 6N and 6J mice, which are often mistakenly referred to interchangeably as “C57BL/6” mice (12). Future metabolic studies incorporating the 6J line, specifically those involving genetic manipulations, should consider the interplay of the gene of interest in the context of background strain, particularly as it relates to NNT loss of function.…”

“…Despite clear genotypic and phenotypic disparity between 6J and 6N mice, the two lines are often referred to interchangeably as “C57BL/6” mice, creating both discrepancy and confusion within the field. To this point, in a recent review of the literature, Fontaine and Davis (12) reported that <50% of studies incorporating a genetic mouse model conducted over the last several years have specifically detailed the background strain used (12). Moreover, because embryonic stem cells derived from 6J mice have low rates of germline transmission, embryonic stem cells derived from 6N donors have at times been used with 6J mice, thus leading to the generation of knockout mice on a mixed background (12).…”

“…To this point, in a recent review of the literature, Fontaine and Davis (12) reported that <50% of studies incorporating a genetic mouse model conducted over the last several years have specifically detailed the background strain used (12). Moreover, because embryonic stem cells derived from 6J mice have low rates of germline transmission, embryonic stem cells derived from 6N donors have at times been used with 6J mice, thus leading to the generation of knockout mice on a mixed background (12). This issue becomes increasingly problematic when selecting the proper control strain, as evidence exists in the literature in which opposite disease susceptibility phenotypes have been observed when comparing a knockout mouse model to wild-type controls on a 6J versus 6N background (13).…”

The Contribution of Nicotinamide Nucleotide Transhydrogenase to Peroxide Detoxification Is Dependent on the Respiratory State and Counterbalanced by Other Sources of NADPH in Liver Mitochondria

“…Indeed, we recently described redox and permeability transition dysfunctions in liver mitochondria from Nnt-mutated C57BL/6J mice (which are homozygous for an allele named Nnt C57BL/6J ) (16). This study provided novel findings that shed light on the theoretical scientific drawbacks of using widely spread Nnt-mutated mice substrains in biomedical research (9,11,12). In this study, we investigated the function of NNT by developing a congenic mouse model (derived from C57BL/6 substrains) bearing the three Nnt genotypes (i.e.…”