Histone variants are key players in shaping chromatin structure, and, thus, in regulating fundamental cellular processes such as chromosome segregation and gene expression. Emerging evidence points towards a role for histone variants in contributing to tumor progression, and, recently, the first cancer-associated mutation in a histone variant-encoding gene was reported. In addition, genetic alterations of the histone chaperones that specifically regulate chromatin incorporation of histone variants are rapidly being uncovered in numerous cancers. Collectively, these findings implicate histone variants as potential drivers of cancer initiation and/or progression, and, therefore, targeting histone deposition or the chromatin remodeling machinery may be of therapeutic value. Here, we review the mammalian histone variants of the H2A and H3 families in their respective cellular functions, and their involvement in tumor biology.

SUMMARY How dermal papilla (DP) niche cells regulate hair follicle progenitors to control hair growth remains unclear. Using Tbx18Cre to target embryonic DP precursors, we ablate the transcription factor Sox2 early and efficiently, resulting in diminished hair shaft outgrowth. We find that DP niche expression of Sox2 controls the migration rate of differentiating hair shaft progenitors. Transcriptional profiling of Sox2 null DPs reveals increased Bmp6 and decreased Bmp inhibitor Sostdc1, a direct Sox2 transcriptional target. Subsequently, we identify upregulated Bmp signaling in knockout hair shaft progenitors and demonstrate that Bmps inhibit cell migration, an effect that can be attenuated by Sostdc1. A shorter and Sox2-negative hair type lacks Sostdc1 in the DP and shows reduced migration and increased Bmp activity of hair shaft progenitors. Collectively, our data identify Sox2 as a key regulator of hair growth that controls progenitor migration by fine-tuning Bmp-mediated mesenchymal-epithelial crosstalk.

Cell state reprogramming during tumor progression complicates accurate diagnosis, compromises therapeutic effectiveness, and fuels metastatic dissemination. We used chromatin accessibility assays and transcriptional profiling during mammary development as an agnostic approach to identify factors that mediate cancer cell state interconversions. We show that fetal and adult basal cells share epigenetic features consistent with multi-lineage differentiation potential. We find that DNA-binding motifs for SOX transcription factors are enriched in chromatin that is accessible in stem/progenitor cells and inaccessible in differentiated cells. In both mouse and human tumors, SOX10 expression correlates with stem/progenitor identity, dedifferentiation, and invasive characteristics. Strikingly, we demonstrate that SOX10 binds to genes that regulate neural crest cell identity, and that SOX10-positive tumor cells exhibit neural crest cell features.

Highlights d Performed single-nucleus (sn)ATAC-seq profiling of fetal and adult mammary cells d snATAC-seq reveals chromatin changes correlating with basal or luminal cell states d Cells with luminal-or basal-oriented chromatin features are evident before birth d A web resource for single-cell profile of embryonic and postnatal mammary development

Choroid plexus epithelial cells (CPECs) have essential developmental and homeostatic roles related to the cerebrospinal fluid (CSF) and blood-CSF barrier they produce. Accordingly, CPEC dysfunction has been implicated in many neurological disorders, such as Alzheimer’s disease, and transplant studies have provided proof-of-concept for CPEC-based therapies. However, such therapies have been hindered by the inability to expand or generate CPECs in culture. During development, CPECs differentiate from preneurogenic neuroepithelial cells and require Bone Morphogenetic Protein (BMP) signaling, but whether BMPs suffice for CPEC induction is unknown. Here we provide evidence for BMP4 sufficiency to induce CPEC fate from neural progenitors derived from mouse embryonic stem cells (ESCs). CPEC specification by BMP4 was restricted to an early time period after neural induction in culture, with peak CPEC competency correlating to neuroepithelial cells rather than radial glia. In addition to molecular, cellular, and ultrastructural criteria, derived CPECs (dCPECs) had functions that were indistinguishable from primary CPECs, including self-assembly into secretory vesicles and integration into endogenous choroid plexus epithelium following intraventricular injection. We then used BMP4 to generate dCPECs from human ESC-derived neuroepithelial cells. These findings demonstrate BMP4 sufficiency to instruct CPEC fate, expand the repertoire of stem cell-derived neural derivatives in culture, and herald dCPEC-based therapeutic applications aimed at the unique interface between blood, CSF, and brain governed by CPECs.