Akt1 regulates Hox gene expression in mouse embryonic fibroblast
Dept. of Medical Science/박사
In mammals, precise spatiotemporal expressions of Hox genes control body pattern and provide positional information along the body axis during embryogenesis. However, the mechanism by which the Hox genes are regulated is poorly understood. To search for novel regulators of the Hox genes, archived gene expression profiles were analyzed from the Gene Expression Omnibus (GEO) database. In a particular dataset, clustered Hox gene expressions were largely altered in Akt1-/- mouse embryonic fibroblasts (MEFs) compared to the wild type, suggesting the hypothesis that Akt1 is required for the proper expression of Hox genes during mouse embryonic development. Therefore, the expressions of all 39 Hox genes were examined with quantitative RT-PCR and it was found that the transcripts of the 5′ Hoxc genes, Hoxc10, 11, 12 and 13 including a noncoding RNA, were upregulated in Akt1 null MEFs. Particularly, the upregulation of Hoxc11 was further confirmed in the Akt1 null embryonic limbs with quantitative RT-PCR and in situ hybridization. To elucidate the molecular mechanism, first, whether forkhead box O (FoxO), an Akt downstream transcription factor, was involved in the expression of the 5’ Hoxc gene in Akt1-/- MEFs was investigated. Knockdown of Foxo1 and Foxo3 failed to repress Hox gene expression in Akt null MEFs. However, epigenetic modifications correlated with Hox gene transcription; DNA hypomethylation at promoter regions and hyperacetylation of histone H3K9, underlined the upregulation of Hoxc11 and 12 in Akt1 null MEFs. From the inhibitor-treated experiment, histone deacetylases (HDAC) might be required for the repression of 5’ Hoxc transcription in Akt1+/+ MEFs. Moreover, histone H3K9 acetyltransferase, GCN5 might have an effect on Hoxc11 expression in Akt1 null MEFs. These results suggest that Akt1 is necessary for the epigenetic regulation of a group of Hox genes during embryogenesis.