MSX1+PDGFRAlow limb mesenchyme-like cells as an efficient stem cell source for human cartilage regeneration.

Degenerative bone disorders have a significant impact on global health, and regeneration of articular cartilage remains a challenge. Existing cell therapies using mesenchymal stromal cells (MSCs) have shown limited efficacy, highlighting the necessity for alternative stem cell sources. Here, we have identified and characterized MSX1+ mesenchymal progenitor cells in the developing limb bud with remarkable osteochondral-regenerative and microenvironment-adaptive capabilities. Single-cell sequencing further revealed the presence of two major cell compositions within the MSX1+ cells, where a distinct PDGFRAlow subset retained the strongest osteochondral competency and could efficiently regenerate articular cartilage in vivo. Furthermore, a strategy was developed to generate MSX1+PDGFRAlow limb mesenchyme-like (LML) cells from human pluripotent stem cells that closely resembled their mouse counterparts, which were bipotential in vitro and could directly regenerate damaged cartilage in a mouse injury model. Together, our results indicated that MSX1+PDGFRAlow LML cells might be a prominent stem cell source for human cartilage regeneration.

CRISPR-GRANT: a cross-platform graphical analysis tool for high-throughput CRISPR-based genome editing evaluation.

BACKGROUD: CRISPR/Cas is an efficient genome editing system that has been widely used for functional genetic studies and exhibits high potential in biomedical translational applications. Indel analysis has thus become one of the most common practices in the lab to evaluate DNA editing events generated by CRISPR/Cas. Several indel analysis tools have been reported, however, it is often required that users have certain bioinformatics training and basic command-line processing capability. RESULTS: Here, we developed CRISPR-GRANT, a stand-alone graphical CRISPR indel analysis tool, which could be easily installed for multi-platforms, including Linux, Windows, and macOS. CRISPR-GRANT offered a straightforward GUI by simple click-and-run for genome editing analysis of single or pooled amplicons and one-step analysis for whole-genome sequencing without the need of data pre-processing, making it ideal for novice lab scientists. Moreover, it also exhibited shorter run-time compared with tools currently available. CONCLUSION: Therefore, CRISPR-GRANT is a valuable addition to the current CRISPR toolkits that significantly lower the barrier for wet-lab researchers to conduct indel analysis from large NGS datasets. CRISPR-GRANT binaries are freely available for Linux (above Ubuntu 16.04), macOS (above High Sierra 10.13) and Windows (above Windows 7) at https://github.com/fuhuancheng/CRISPR-GRANT . CRISPR-GRANT source code is licensed under the GPLv3 license and free to download and use.

Dental niche cells directly contribute to tooth reconstitution and morphogenesis.

Mammalian teeth develop from the inductive epithelial-mesenchymal interaction, an important mechanism shared by many organs. The cellular basis for such interaction remains elusive. Here, we generate a dual-fluorescence model to track and analyze dental cells from embryonic to postnatal stages, in which Pitx2+ epithelium and Msx1+ mesenchyme are sufficient for tooth reconstitution. Single-cell RNA sequencing and spatial mapping further revealed critical cellular dynamics during molar development, where tooth germs are organized by Msx1+Sdc1+ dental papilla and surrounding dental niche. Surprisingly, niche cells are more efficient in tooth reconstitution and can directly regenerate papilla cells through interaction with dental epithelium. Finally, from the dental niche, we identify a group of previously unappreciated migratory Msx1+ Sox9+ cells as the potential cell origin for dental papilla. Our results indicate that the dental niche cells directly contribute to tooth organogenesis and provide critical insights into the essential cell composition for tooth engineering.

Scramblases and virus infection.

The asymmetric distribution of lipids, maintained by flippases/floppases and scramblases, plays a pivotal role in various physiologic processes. Scramblases are proteins that move phospholipids between the leaflets of the lipid bilayer of the cellular membrane in an energy-independent manner. Recent studies have indicated that viral infection is closely related to cellular lipid distribution. The level and distribution of phosphatidylserine (PtdSer) in cells have been demonstrated to be critical regulators of viral infections. Previous studies have supported that the infection of human immunodeficiency virus (HIV), Zika virus, Ebola virus (EBOV), influenza virus, and dengue fever virus require the externalization of phospholipids mediated by scramblases, which are also involved in the pathogenicity of the pandemic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In this review, we review the relationship of scramblases with viruses and the potential viral effector proteins that might utilize host scramblases.