Adult Prg4+ progenitors repair long-term articular cartilage wounds in vivo.

The identity and origin of the stem/progenitor cells for adult joint cartilage repair remain unknown, impeding therapeutic development. Simulating the common therapeutic modality for cartilage repair in humans, i.e., full-thickness microfracture joint surgery, we combined the mouse full-thickness injury model with lineage tracing and identified a distinct skeletal progenitor cell type enabling long-term (beyond 7 days after injury) articular cartilage repair in vivo. Deriving from a population with active Prg4 expression in adulthood while lacking aggrecan expression, these progenitors proliferate, differentiate to express aggrecan and type II collagen, and predominate in long-term articular cartilage wounds, where they represent the principal repair progenitors in situ under native repair conditions without cellular transplantation. They originate outside the adult bone marrow or superficial zone articular cartilage. These findings have implications for skeletal biology and regenerative medicine for joint injury repair.

NC10 bacteria in marine oxygen minimum zones.

Bacteria of the NC10 phylum link anaerobic methane oxidation to nitrite denitrification through a unique O2-producing intra-aerobic methanotrophy pathway. A niche for NC10 in the pelagic ocean has not been confirmed. We show that NC10 bacteria are present and transcriptionally active in oceanic oxygen minimum zones (OMZs) off northern Mexico and Costa Rica. NC10 16S rRNA genes were detected at all sites, peaking in abundance in the anoxic zone with elevated nitrite and methane concentrations. Phylogenetic analysis of particulate methane monooxygenase genes further confirmed the presence of NC10. rRNA and mRNA transcripts assignable to NC10 peaked within the OMZ and included genes of the putative nitrite-dependent intra-aerobic pathway, with high representation of transcripts containing the unique motif structure of the nitric oxide (NO) reductase of NC10 bacteria, hypothesized to participate in O2-producing NO dismutation. These findings confirm pelagic OMZs as a niche for NC10, suggesting a role for this group in OMZ nitrogen, methane and oxygen cycling.