Highlights d Loss of CDR1as expression promotes melanoma invasion and metastasis d CDR1as arises from a lncRNA that is epigenetically silenced by EZH2/PRC2 d CDR1as interactor, IGF2BP3, largely mediates the effects of CDR1as loss in melanoma d CDR1as levels associate with cell states and therapeutic sensitivities

The total hyaluronan content has been determined in rats. The animals were frozen and sectioned in a cryostat before digestion with papain and pronase. The hyaluronan content was determined by a specific radioassay and it was found that 250 g rats contained 40-60 mg of the polysaccharide. The recovery from the preparation procedure was close to 100%, as determined from tracer experiments. More than half of the hyaluronan was found in skin, approximately one quarter in the skeleton and supporting structures and less than one tenth in skeletal muscle. Based on calculated lymph flow and lymph concentration of hyaluronan, it seems that a significant fraction of the total hyaluronan in skin (greater than 1%) is removed via the lymphatics in a 24 h period. An attempt was made to isolate undegraded hyaluronan from rat skin by gentle methods giving full recovery in order to estimate the molecular weight of the polysaccharide. Hyaluronan was recovered quantitatively, but as determined from added tracer, it had been degraded. Correction for the estimated degradation gave a molecular weight of several millions for the endogenous hyaluronan.

A radioassay for sodium hyaluronate using high-affinity binding protein from bovine cartilage has been modified for serum analysis. The accuracy of the method was checked by isotope dilution experiments and by recovery studies with exogenous hyaluronate. The between-assay standard deviation in the determination is 15-20%. The concentration of sodium hyaluronate in healthy adults (blood donors) is in the range of 10 to 100 micrograms/l with a mean value in the order of 30 to 40 micrograms/l. This is a lower concentration than previously reported. The same level was found in young people. Higher hyaluronate concentrations were noted in persons above 50 years of age. Analysis of plasma showed a slightly higher average hyaluronate level (5%) than in serum from the same persons. There were no notable sex differences. Analysis of serum and plasma from adult animals (rat, rabbit, dog, pig, goat, sheep, cow and horse) gave hyaluronate concentrations of the same order or higher than in human serum.

Human lymph was collected from patients with leaking lymph vessels after thoracic surgery. Ovine lymph was obtained from the mesenteric, lumbar, popliteal and prescapular lymph ducts by cannulation. The concentration of hyaluronate varied considerably (between 0.2 and 50 mg/l) and the highest concentrations were found in mesenteric lymph. The Mr of the polysaccharide showed a great polydispersity and variation between individuals and in different regions of the lymphatic system. High-Mr hyaluronate (greater than 10(6) was present in lymph both from man and sheep. Hyaluronate was also isolated by affinity chromatography in 70-80% yield from human serum and plasma obtained from healthy individuals and patients with rheumatoid arthritis and primary biliary cirrhosis. The weight (Mw)- and number (Mn)-average relative molecular masses were roughly the same in the three groups [(1.4-2.7) X 10(5) and (2.1-5.7) X 10(4) respectively]. The low Mr of hyaluronate in blood compared with that in lymph is explained by a preferential uptake of the large molecules by the liver endothelial cells.

Mechanisms of plasticity to acquire different cell fates are critical for adult stem cell (SC) potential, yet are poorly understood. Reduced global histone methylation is an epigenetic state known to mediate plasticity in cultured embryonic SCs and T-cell progenitors. Here we find histone H3 K4/K9/K27me3 levels actively reduced in adult mouse skin and hair follicle stem cells (HFSCs) during G0 quiescence. The level of marks over specific gene promoters did not correlate to mRNA level changes in quiescent HFSCs. Skin hypomethylation during quiescence was necessary for subsequent progression of hair homeostasis (cycle). Inhibiting BMP signal, a known HFSC anti-proliferative factor, elevated HFSC methylation in vivo during quiescence prior to proliferation onset. Furthermore, removal of proliferation factors and addition of BMP4 reduced histone methylases and increased demethylases mRNAs in cultured skin epithelial cells. We conclude that signalling couples hair follicle stem cell quiescence with reduced H3 K4/K9/K27me3 levels for proper tissue homeostasis.

Runx1 controls timing of adult HSFC and short-term progenitor emergence in the embryonic epithelium and HFSC differentiation and long-term skin integrity in embryonic mesenchyme.

Pluripotent stem cells (PSC) hold great promise for the treatment of human skeletal muscle diseases. However, it remains challenging to convert PSC to skeletal muscle cells, and the mechanisms by which the master regulatory transcription factor, Pax7, promotes muscle stem (satellite) cell identity are not yet understood. We have taken advantage of PSC-derived skeletal muscle precursor cells (iPax7), wherein the induced expression of Pax7 robustly initiates the muscle program and enables the in vitro generation of precursors that seed the satellite cell compartment upon transplantation. Remarkably, we found that chromatin accessibility in myogenic precursors pre-figures subsequent activation of myogenic differentiation genes. We also found that Pax7 binding is generally restricted to euchromatic regions and excluded from H3K27 tri-methylated regions in muscle cells, suggesting that recruitment of this factor is circumscribed by chromatin state. Further, we show that Pax7 binding induces dramatic, localized remodeling of chromatin characterized by the acquisition of histone marks associated with enhancer activity and induction of chromatin accessibility in both muscle precursors and lineage-committed myoblasts. Conversely, removal of Pax7 leads to rapid reversal of these features on a subset of enhancers. Interestingly, another cluster of Pax7 binding sites is associated with a durably accessible and remodeled chromatin state after removal of Pax7, and persistent enhancer accessibility is associated with subsequent, proximal binding by the muscle regulatory factors, MyoD1 and myogenin. Our studies provide new insights into the epigenetic landscape of skeletal muscle stem cells and precursors and the role of Pax7 in satellite cell specification.

Mechanisms of tissue stem cell (SC) quiescence control are important for normal homeostasis and for preventing cancer. Cyclin-dependent kinase inhibitors (CDKis) are known inhibitors of cell cycle progression. We document CDKis expression in vivo during hair follicle stem cell (HFSC) homeostasis and find p21 (cyclin-dependent kinase inhibitor 1a, Cdkn1a), p57, and p15 up-regulated at quiescence onset. p21 appears important for HFSC timely onset of quiescence. Conversely, we find that Runx1 (runt related transcription factor 1), which is known for promoting HFSC proliferation, represses p21, p27, p57, and p15 transcription in HFSC in vivo. Intriguingly, in cell culture, tumors, and normal homeostasis, Runx1 and p21 interplay modulates proliferation in opposing directions under the different conditions. Unexpectedly, Runx1 and p21 synergistically limit the extent of HFSC quiescence in vivo, which antagonizes the role of p21 as a cell cycle inhibitor. Importantly, we find in cultured keratinocytes that Runx1 and p21 bind to the p15 promoter and synergistically repress p15 mRNA transcription, thereby restraining cell cycle arrest. This documents a surprising ability of a CDKi (p21) to act as a direct transcriptional repressor of another CDKi (p15). We unveil a robust in vivo mechanism that enforces quiescence of HFSCs, and a context-dependent role of a CDKi (p21) to limit quiescence of SCs, potentially by directly down-regulating mRNA levels of (an)other CDKi(s).AML1 | skin | malignancy | pulse-chase | H2B-GFP