Fibroblast growth factor 10 (FGF10) is well established as a mesenchyme-derived growth factor and a critical regulator of fetal organ development in mice and humans. Using a single-cell RNA sequencing (RNA-seq) atlas of salivary gland (SG) and a tamoxifen inducible Fgf10CreERT2:R26-tdTomato mouse, we show that FGF10pos cells are exclusively mesenchymal until postnatal day 5 (P5) but, after P7, there is a switch in expression and only epithelial FGF10pos cells are observed after P15. Further RNA-seq analysis of sorted mesenchymal and epithelial FGF10pos cells shows that the epithelial FGF10pos population express the hallmarks of ancient ionocyte signature Forkhead box i1 and 2 (Foxi1, Foxi2), Achaete-scute homolog 3 (Ascl3), and the cystic fibrosis transmembrane conductance regulator (Cftr). We propose that epithelial FGF10pos cells are specialized SG ionocytes located in ducts and important for the ionic modification of saliva. In addition, they maintain FGF10-dependent gland homeostasis via communication with FGFR2bpos ductal and myoepithelial cells.
Phago- and endocytosis have been studied in the colourless flagellate T. lauterborni using electron microscope. The coated pits are formed on the dorsal surface of the cells and in the flagellar pocket; then they are transformed into coated vesicles and transported into the ventral part of the cell loosing their clathrin coat. The storing of small vesicles in the ventral groove region is constant. To begin to feed a flagellate stops and produces within several seconds long ramified filopodia from the ventral groove. These filopodia serve to phagocyte bacteria. Small ventral vesicles represent the membrane pull which is necessary for a quick formation of the vast surface of filopodia. By means of peroxidase reaction in was shown that these vesicles were of endocytotic origin, rather than being the product of the Golgi apparatus functioning.
Uncontrolled fibroblast growth factor (FGF) signaling can lead to human diseases, necessitating multiple layers of self-regulatory control mechanisms to keep its activity in check. Herein, we demonstrate that FGF9 and FGF20 ligands undergo a reversible homodimerization, occluding their key receptor binding sites. To test the role of dimerization in ligand autoinhibition, we introduced structure-based mutations into the dimer interfaces of FGF9 and FGF20. The mutations weakened the ability of the ligands to dimerize, effectively increasing the concentrations of monomeric ligands capable of binding and activating their cognate FGF receptor in vitro and in living cells. Interestingly, the monomeric ligands exhibit reduced heparin binding, resulting in their increased radii of heparan sulfate-dependent diffusion and biologic action, as evidenced by the wider dilation area of ex vivo lung cultures in response to implanted mutant FGF9-loaded beads. Hence, our data demonstrate that homodimerization autoregulates FGF9 and FGF20's receptor binding and concentration gradients in the extracellular matrix. Our study is the first to implicate ligand dimerization as an autoregulatory mechanism for growth factor bioactivity and sets the stage for engineering modified FGF9 subfamily ligands, with desired activity for use in both basic and translational research.
Recent studies have shown that various neural and embryonic stem cells cultured in 1-8% oxygen (O(2)), levels lower than those typically used in cell culture (20.9%), displayed increased rates of proliferation; however, the molecular mechanisms underlying these changes are largely undefined. In this study, using rigorously controlled O(2) levels, we found that neural stem cells (NSCs) from embryonic day 15 rat cortex increased their rate of proliferation and migration in 1% O(2) relative to 20% O(2) without changes in viability. We sought to identify molecular changes in NSCs grown in 1% O(2) that might account for these increases. In 1% O(2), levels of the hypoxia-inducible transcription factor HIF-1α were transiently increased. Reduced adherence of NSCs in 1% O(2) to basement membrane-coated plates was observed, and quantitative RT-PCR analysis confirmed that the levels of mRNA for an assortment of cell adhesion and extracellular matrix molecules were altered. Most notable was a 5-fold increase in matrix metalloproteinase (MMP)-9 mRNA. Specific inhibition of MMP-9 activity, verified using a fluorescent substrate assay, prevented the increase in proliferation and migration in 1% O(2). The canonical Wnt pathway was recently shown to be activated in stem cells in low O(2) via HIF-1α. Inhibition of Wnt signaling by DKK-1 also prevented the increase in proliferation, migration, and MMP-9 expression. Thus, MMP-9 is a key molecular effector, downstream of HIF-1α and Wnt activation, responsible for increased rates of NSC proliferation and migration in 1% O(2).
Aging is a complex biological process in which many organs are pathologically affected. We previously reported that aged C57BL/6J had increased lacrimal gland (LG) lymphoid infiltrates that suggest ectopic lymphoid structures. However, these ectopic lymphoid structures have not been fully investigated. Using C57BL/6J mice of different ages, we analyzed the transcriptome of aged murine LGs and characterized the B and T cell populations. Age-related changes in the LG include increased differentially expressed genes associated with B and T cell activation, germinal center formation, and infiltration by marginal zone-like B cells. We also identified an age-related increase in B1
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