A novel reporter mouse line for studying alveolar macrophages

Alveolar macrophages(AMs)are self-maintained immune cells that play vital roles in lung homeostasis and immunity.Although reporter mice and culture systems have been established for studying macrophages,an accurate and specific reporter line for alveolar macrophage study is still not available.Here we reported a novel Rspo1-tdTomato gene reporter mouse line that could specifically label mouse AMs in a cell-intrinsic manner.Using this reporter system,we visualized the dynamics of alveolar macrophages intravitally under steady state and characterized the alveolar macrophage differentiation under in vitro condition.By performing ATAC-seq,we found that insertion of the tdTomato cassette in the Rspo1 locus increased the accessibility of a PPARE motif within the Rspo1 locus and revealed a potential regulation by key transcription factor PPAR-γfor alveolar macrophage differentiation in vitro and in vivo.Consistently,perturbation of PPAR-γby its agonist rosiglitazone or inhibitor GW9662 resulted in corresponding alteration of tdTomato expression in alveolar macrophages together with the transcription of PPAR-γdownstream target genes.Furthermore,global transcriptomic analyses of AMs from the wild type mice and the Rspo1-tdTomato mice showed comparable gene expression profiles,especially those AM-specific genes,confirming that the insertion of the tdTomato cassette in the Rspo1 locus does not impact the cell identity and biological function of AMs under normal condition.Taken together,our study provides an alternative tool for in vivo and in vitro labeling of alveolar macrophages with high specificity which could also be utilized as an indicator of PPAR-γactivity for future development of PPAR-γspecific targeting drugs.

Genetic reporter analysis reveals an expandable reservoir of OCT4+cells in adult skin

The transcription factor Oct4(Pou5f1)is a critical regulator of pluripotency in embryonic and induced pluripotent stem cells.Therefore,Oct4 expression might identify somatic stem cell populations with inherent multipotent potential or a propensity for facilitated reprogramming.However,analysis of Oct4 expression is confounded by Oct4 pseudogenes or non-pluripotency-related isoforms.Systematic analysis of a transgenic Oct4-EGFP reporter mouse identified testis and skin as two principle sources of Oct4^(+)cells in postnatal mice.While the prevalence of GFP^(+)cells in testis rapidly declined with age,the skin-resident GFP^(+)population expanded in a cyclical fashion.These cells were identified as epidermal stem cells dwelling in the stem cell niche of the hair follicle,which endogenously expressed all principle reprogramming factors at low levels.Interestingly,skin wounding or non-traumatic hair removal robustly expanded the GFP^(+)epidermal cell pool not only locally,but also in uninjured skin areas,demonstrating the existence of a systemic response.Thus,the epithelial stem cell niche of the hair follicle harbors an expandable pool of Oct4^(+)stem cells,which might be useful for therapeutic cell transfer or facilitated reprogramming.