Mesenchyme-specific loss of Dot1L histone methyltransferase leads to skeletal dysplasia phenotype in mice.

Chromatin modifying enzymes play essential roles in skeletal development and bone maintenance, and deregulation of epigenetic mechanisms can lead to skeletal growth and malformation disorders. Here, we report a novel skeletal dysplasia phenotype in mice with conditional loss of Disruptor of telomeric silencing 1-like (Dot1L) histone methyltransferase in limb mesenchymal progenitors and downstream descendants. Phenotypic characterizations of mice with Dot1L inactivation by Prrx1-Cre (Dot1L-cKO) revealed limb shortening, abnormal bone morphologies, and forelimb dislocations. Our in vivo and in vitro data support a crucial role for Dot1L in regulating growth plate chondrocyte proliferation and differentiation, extracellular matrix production, and secondary ossification center formation. Micro-computed tomography analysis of femurs revealed that partial loss of Dot1L expression is sufficient to impair trabecular bone formation and microarchitecture in young mice. Moreover, RNAseq analysis of Dot1L deficient chondrocytes implicated Dot1L in the regulation of key genes and pathways necessary to promote cell cycle regulation and skeletal growth. Collectively, our data show that early expression of Dot1L in limb mesenchyme provides essential regulatory control of endochondral bone morphology, growth, and stability.