| Summary: | Fibroblast growth factor 10 (FGF10) is a paracrine molecule, serving crucial mesenchymal-to-epithelial signalling roles during development and postnatally. FGF10 binds specifically to FGF-receptor 2 IIIb (FGFR2-IIIb) and their interaction results in signal transduction pathways, which promote epithelial proliferation, motility and survival. Human heterozygous mutations in the Fgf10 gene result in LADD (lacrimo-auriculo-dento-digital) and ALSG (aplasia of lacrimal and salivary glands) syndromes, which to date have been solely attributed to perturbed FGF10 paracrine function. However, the molecular dynamics undelaying LADD-causing G138E FGF10 mutation, which falls outside its receptor interaction interface, has remained enigmatic. Moreover, Fgf10 is expressed within mouse hypothalamus, which is not accompanied by expression of its cognate receptor, signifying FGF10 may have additional intracrine function. In this study, FGF10 was investigated in a context of nuclear translocation and putative endogenous function within mesenchymal and hypothalamic cells. Through interrogation of FGF10’s sequence and subcellular distribution, the protein was found to possess two putative nuclear localization sequences, termed NLS1 and NLS2, which were shown implicated in nuclear translocation of FGF10. Furthermore, the protein was found localising to the cell nucleolus. Subsequent examination of the LADD-causing G138E, through site-directed mutagenesis, revealed its curious positioning within NLS1 and its role in abrogation of both, nuclear and secretory function of the FGF10. Additionally, specific combinatorial mutations within NLS2 abolished the protein’s nuclear translocation, yet did not diminish the protein’s progression through the secretory pathway, showing importance of this motif in the nuclear transport of FGF10. Interestingly, endogenous FGF10 was shown to disrupt differentiation of mesenchymal chondrogenitors, whereas externally applied protein caused the opposite effect, promoting cell differentiation, suggesting contrary function of paracrine and nuclear FGF10. Moreover, novel culture of hypothalamic Fgf10 expressing tanycytes derived from transgenic mice was generated and characterised, showing that intracrine FGF10 may be potentially implicated in control of cell cycle of neural stem cells.
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