The Histidine Triad Protein Hint Is Not Required for Murine Development or Cdk7 Function

Abstract

The histidine triad (HIT) protein Hint has been found to associate with mammalian Cdk7, as well as to interact both physically and genetically with the budding yeast Cdk7 homologue Kin28. To study the function of Hint and to explore its possible role in modulating Cdk7 activity in vivo, we have characterized the expression pattern of murine Hint and generated Hint-deficient (Hint^−/−) mice. Hint was widely expressed during mouse development, with pronounced expression in several neuronal ganglia, epithelia, hearts, and testes from embryonic day 15 onward. Despite this widespread expression, disruption of Hint did not impair murine development. Moreover, Hint-deficient mice had a normal life span and were apparently healthy. Histological examination of tissues with high Hint expression in wild-type animals did not show signs of abnormal pathology in Hint ^−/− mice. Functional redundancy within the HIT family was addressed by crossing Hint ^−/− mice with mice lacking the related HIT protein, Fhit, and by assaying the expression levels of the HIT protein gene family members Hint2 and Hint3 in Hint ^+/+ and Hint ^−/− tissues. Finally, Cdk7 kinase activity and cell cycle kinetics were found to be comparable in wild-type and Hint ^−/− mouse embryonic fibroblasts, suggesting that Hint may not be a key regulator of Cdk7 activity.

ACKNOWLEDGMENTS

We thank Peter Lonai for the PGK-Cre mice, Pierre Plateau for the HNT2 S. cerevisiae disruptant strain, and Bernard Weinstein for Hint antibodies. Ari Ristimäki, Matti Haltia, and Kirsi Sainio are acknowledged for consultation. Birgitta Tjäder, Susanna Räsänen, and Sanna Kihlberg are acknowledged for excellent technical assistance.

N.K. and D.J.R contributed equally to this work.

This study was supported by grants from Biocentrum Helsinki, the Finnish Cancer Organization, the Sigrid Juselius Foundation, TEKES, and the Academy of Finland. N.K. was supported by the Helsinki Graduate School in Biotechnology and Molecular Biology, and D.J.R. was supported by the Helsinki Biomedical Graduate School.