Uhrf1 is indispensable for normal limb growth by regulating chondrocyte differentiation

Chondrocyte differentiation is regulated at a transcriptional level and by various hormonal stimuli. Since chondrocyte differentiation is important for normal skeletal growth, inadequate amounts of differentiation can lead to pathological conditions such as osteoarthritis. Transcriptional regulation can be tightly orchestrated by epigenetic regulators. Among these, ubiquitin-like with PHD and RING finger domains 1 (Uhrf1) is reported to have diverse epigenetic functions, including regulation of DNA methylation. However, the physiological functions of Uhrf1 in skeletal tissues remain unclear. Here we show that limb mesenchymal cell-specific Uhrf1 conditional knockout mice (Uhrf1?Limb/?Limb) exhibit shortened long bones that have morphological deformities due to impaired chondrocyte differentiation and proliferation. RNA-seq performed on primary cultured chondrocytes obtained from control and Uhrf1?Limb/?Limb mice revealed that expression levels of proliferative chondrocyte marker genes were downregulated, whereas hypertrophic chondrocyte marker genes were upregulated. In addition, gene ontology analyses and Gene Set Enrichment Analysis (GSEA) suggested that limb growth retardation due to compromised chondrocyte differentiation might be caused by increased activity of the focal adhesion signaling pathway. These results indicated that Uhrf1 has a crucial role in normal skeletal maturation by coordinating transcriptional regulatory networks during chondrocyte differentiation. Overall design: mRNA profiles of primary chondrocytes obtained from 3-day old Control and Uhrf1 cKO mice were generated by deep sequencing, in triplicate, using Illumina Miseq. Sequence data were mapped on the mouse genome (mm10) using Tophat and analyzed by Cufflinks.