Reconstructing the chondro-osteoblastic lineage by single cell RNA-seq

Abstract

Reconstructing the chondro-osteoblastic lineage by single cell RNA-seq Kwok Yeung Tsang1, Xiangyu Li2, Jin Gu2, Danny Chan1, Michael Q. Zhang2,3, Kathryn SE Cheah1 1School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China. 2Bioinformatics Division, Center for Synthetic and Systems Biology, TNLIST, Tsinghua University, Beijing, China. 3Department of Molecular and Cell Biology, Center for Systems Biology, The University of Texas at Dallas, Richardson, TX, 75080, U.S.A. During mammalian endochondral bone formation, growth plate cartilage laid down by chondrocytes is replaced with bone produced by osteoblasts. Although these two cell types were thought to be distinct lineages that are descendants of a common mesenchymal progenitor, we and others have recently revealed a chondrocyte-osteoblast continuum during endochondral bone formation. In this process hypertrophic chondrocytes survive during the cartilage-to-bone transition and contribute to all osteoblast lineages. However, molecular control of the lineage progression is unclear. We have applied single cell transcriptomics to identify lineage intermediates during the chondrocyte to osteoblast transition. We manually isolated fluorescently-tagged single cells of this lineage from the proximal tibias of three neonatal pups, and then generated transcriptomic data for 101 single cells. Principal component analysis and hierarchical clustering identified subpopulations expressing distinct chondrocyte-like, osteoblast-like and intermediate molecular signatures. Amongst these subpopulations were some cells which are proliferating progenitors and expressed mesenchymal/stromal cell markers. Therefore, single cell transcriptome analysis serves as a powerful tool to elucidate lineage hierarchy and provides important insights into the transition from chondrocyte to osteoblastic lineage in bone development.