A single cell transcriptional atlas of early synovial joint development

Synovial joint development begins with the formation of the interzone, a region of condensed mesenchymal cells at the site of the prospective joint. Recently, lineage tracing strategies have revealed that Gdf5-lineage cells native to and from outside the interzone contribute to most, if not all, of the major joint components. However, there is limited knowledge of the specific transcriptional and signaling programs that regulate interzone formation and fate diversification of synovial joint constituents. To address this, we have performed single cell RNA-Seq analysis of 7,329 synovial joint progenitor cells from the developing murine knee joint from E12.5 to E15.5. By using a combination of computational analytics, in situ hybridization, and in vitro characterization of prospectively isolated populations, we have identified the transcriptional profiles of the major developmental paths for joint progenitors. Our freely available single cell transcriptional atlas will serve as a resource for the community to uncover transcriptional programs and cell interactions that regulate synovial joint development. We sampled Gdf5-lineage cells of the murine knee at embryonic time points e12.5, e13.5, e14.5, and e15.5 and subjected them to single cell RNAseq analysis via 10x.滑膜关节（synovial joint）的发育始于间区（interzone）的形成，该结构是未来关节位点处的致密间充质细胞区域。近年来，谱系示踪策略已证实，源自间区内外的Gdf5谱系细胞可参与构成关节绝大多数（乃至全部）主要组成组分。然而，目前学界对于调控间区形成以及滑膜关节组成细胞命运分化的特异性转录与信号通路程序，认知仍较为有限。为填补这一研究空白，我们对胚胎发育阶段E12.5至E15.5的小鼠膝关节发育过程中的7329个滑膜关节祖细胞开展了单细胞RNA测序（single cell RNA-Seq）分析。我们结合计算分析、原位杂交（in situ hybridization）以及对前瞻性分选细胞群体的体外（in vitro）表征，明确了关节祖细胞主要发育路径的转录谱特征。本研究公开免费提供的单细胞转录图谱将为全球科研共同体提供宝贵的研究资源，助力揭示调控滑膜关节发育的转录程序与细胞互作机制。我们采集了胚胎时间点E12.5、E13.5、E14.5及E15.5的小鼠膝关节Gdf5谱系细胞，并通过10x技术对其进行了单细胞RNA测序分析。