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Krüppel-like factor 5 (Klf5) is a zinc-finger transcription factor that controls various biological processes, including cell proliferation and differentiation. We show that Klf5 is also an essential mediator of skeletal muscle regeneration and myogenic differentiation. During muscle regeneration after injury (cardiotoxin injection), Klf5 was induced in the nuclei of differentiating myoblasts and newly formed myofibers expressing myogenin in vivo. Satellite cell-specific Klf5 deletion severely impaired muscle regeneration, and myotube formation was suppressed in Klf5-deleted cultured C2C12 myoblasts and satellite cells. Klf5 knockdown suppressed induction of muscle differentiation-related genes, including myogenin. Klf5 ChIP-seq revealed that Klf5 binding overlaps that of MyoD and Mef2, and Klf5 physically associates with both MyoD and Mef2. In addition, MyoD recruitment was greatly reduced in the absence of Klf5. These results indicate that Klf5 is an essential regulator of skeletal muscle differentiation, acting in concert with myogenic transcription factors such as MyoD and Mef2.DOI: http://dx.doi.org/10.7554/eLife.17462.001

Aspergillus nidulans can utilize carbon sources that result in the production of TCA cycle intermediates, thereby requiring gluconeogenesis. We have cloned the acuG gene encoding fructose-1,6 bisphosphatase and found that expression of this gene is regulated by carbon catabolite repression as well as by induction by a TCA cycle intermediate similar to the induction of the previously studied acuF gene encoding phosphoenolpyruvate carboxykinase. The acuN356 mutation results in loss of growth on gluconeogenic carbon sources. Cloning of acuN has shown that it encodes enolase, an enzyme involved in both glycolysis and gluconeogenesis. The acuN356 mutation is a translocation with a breakpoint in the 59 untranslated region resulting in loss of expression in response to gluconeogenic but not glycolytic carbon sources. Mutations in the acuK and acuM genes affect growth on carbon sources requiring gluconeogenesis and result in loss of induction of the acuF, acuN, and acuG genes by sources of TCA cycle intermediates. Isolation and sequencing of these genes has shown that they encode proteins with similar but distinct Zn(2) Cys(6) DNA-binding domains, suggesting a direct role in transcriptional control of gluconeogenic genes. These genes are conserved in other filamentous ascomycetes, indicating their significance for the regulation of carbon source utilization.

Summary The ability of fungi to use carbon sources metabolized via the TCA cycle requires gluconeogenesis. In Aspergillus nidulans the AcuK and AcuM transcription factors regulate the expression of the gluconeogenic genes acuF, encoding phosphoenolpyruvate carboxykinase, and acuG, encoding fructose‐1,6‐bisphosphatase. Expressed proteins containing the AcuK/AcuM N‐terminal DNA‐binding domains bind together in vitro to motifs containing repeats of CGG separated by seven bases (CCGN7CCG) and the functionality of these sequences was verified in vivo by acuF–lacZ reporter studies. Chromatin immunoprecipitation analysis showed inter‐dependent DNA binding of the proteins to the promoters of gluconeogenic genes in vivo independent of the carbon source. Deletion of the mdhC gene encoding a cytoplasmic/peroxisomal malate dehydrogenase showed that this activity is not essential for gluconeogenesis and indicated that induction of AcuK/AcuM regulated genes might result from malate accumulation. Deletion of the gene for the alternative oxidase did not affect growth on gluconeogenic carbon sources; however, expression was absolutely dependent on AcuK and AcuM. Orthologues of AcuK and AcuM, are present in a wide range of fungal taxa and the CCGN7CCG motif is present in the 5′ of many genes involved in gluconeogenesis indicating a fundamental role for these transcription factors in reprogramming fungal carbon metabolism.

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