Absence of Evidence Is Not Evidence of Absence
Pitfalls of Cre Knock-Ins in the c-Kit Locus
c-Kit+ Cells Minimally Contribute Cardiomyocytes to the Heart van Berlo et al Nature. 2014;509:337–341.
A recent article by Jeffrey Molkentin’s group using mice with Cre/lox knockin in the c-kit locus concludes that, contrary to other reports, c-kit+ cells minimally contribute cardiomyocytes to the heart. We think that the interpretation of the results of the author is problematic because critical data to support their conclusions have not been provided.
Recently, van Berlo et al1 published an article in Nature entitled c-kit+ Cells Minimally Contribute Cardiomyocytes to the Heart, in which they assessed the contribution of c-kit–expressing cell lineages to the formation of cardiomyocytes and microvasculature in the myocardium during development, aging, and after myocardial infarction. The authors knocked in the c-kit locus, a constitutive Cre-IRES-nGFP (cyclic recombination enzyme linked to an internal ribosome entry site driving a nuclear green fluorescent protein), in one line of mice and a tamoxifen-inducible mER (membrane estrogen receptor)-Cre-mER in another line. Both gene knockins placed the CRE sequence in frame with the ATG start codon in exon 1 of the Kit gene. These mice were cross-bred with the ROSA26 reporter (R26R) mutated mice carrying a floxed (and Cre dependent) reporter gene (either green fluorescent protein or mT/mG construct). On the basis of a limited set of experiments, the authors concluded that although cardiac c-kit+ cells contribute cardiomyocytes, they do so minimally (from ≈0.001% to ≈0.02%) and, therefore, it was considered to be functionally insignificant. By contrast, c-kit+ cells amply generated cardiac endothelial cells. From these data, the authors concluded that the use of c-kit+ cells in myocardial repair and regeneration protocols should be reconsidered.
Interestingly, this article comes out at a particularly propitious time to challenge the regenerative properties of the c-kit+ cardiac progenitor cells. During the past several months, a flurry of negative reports in the scientific and lay press has predicted the demise of stem cell–based regenerative …