The FU gene and its possible protein isoforms

BACKGROUND: FU is the human homologue of the Drosophila gene fused whose product fused is a positive regulator of the transcription factor Cubitus interruptus (Ci). Thus, FU may act as a regulator of the human counterparts of Ci, the GLI transcription factors. Since Ci and GLI are targets of Hedgehog signaling in development and morphogenesis, it is expected that FU plays an important role in Sonic, Desert and/or Indian Hedgehog induced cellular signaling. RESULTS: The FU gene was identified on chromosome 2q35 at 217.56 Mb and its exon-intron organization determined. The human developmental disorder Syndactyly type 1 (SD1) maps to this region on chromosome 2 and the FU coding region was sequenced using genomic DNA from an affected individual in a linked family. While no FU mutations were found, three single nucleotide polymorphisms were identified. The expression pattern of FU was thoroughly investigated and all examined tissues express FU. It is also clear that different tissues express transcripts of different sizes and some tissues express more than one transcript. By means of nested PCR of specific regions in RT/PCR generated cDNA, it was possible to verify two alternative splicing events. This also suggests the existence of at least two additional protein isoforms besides the FU protein that has previously been described. This long FU and a much shorter isoform were compared for the ability to regulate GLI1 and GLI2. None of the FU isoforms showed any effects on GLI1 induced transcription but the long form can enhance GLI2 activity. Apparently FU did not have any effect on SUFU induced inhibition of GLI. CONCLUSIONS: The FU gene and its genomic structure was identified. FU is a candidate gene for SD1, but we have not identified a pathogenic mutation in the FU coding region in a family with SD1. The sequence information and expression analyses show that transcripts of different sizes are expressed and subjected to alternative splicing. Thus, mRNAs may contain different 5'UTRs and encode different protein isoforms. Furthermore, FU is able to enhance the activity of GLI2 but not of GLI1, implicating FU in some aspects of Hedgehog signaling

Maintenance of Taste Organs Is Strictly Dependent on Epithelial Hedgehog/GLI Signaling

<div><p>For homeostasis, lingual taste papilla organs require regulation of epithelial cell survival and renewal, with sustained innervation and stromal interactions. To investigate a role for Hedgehog/GLI signaling in adult taste organs we used a panel of conditional mouse models to manipulate GLI activity within epithelial cells of the fungiform and circumvallate papillae. Hedgehog signaling suppression rapidly led to taste bud loss, papilla disruption, and decreased proliferation in domains of papilla epithelium that contribute to taste cells. Hedgehog responding cells were eliminated from the epithelium but retained in the papilla stromal core. Despite papilla disruption and loss of taste buds that are a major source of Hedgehog ligand, innervation to taste papillae was maintained, and not misdirected, even after prolonged GLI blockade. Further, vimentin-positive fibroblasts remained in the papilla core. However, retained innervation and stromal cells were not sufficient to maintain taste bud cells in the context of compromised epithelial Hedgehog signaling. Importantly taste organ disruption after GLI blockade was reversible in papillae that retained some taste bud cell remnants where reactivation of Hedgehog signaling led to regeneration of papilla epithelium and taste buds. Therefore, taste bud progenitors were either retained during epithelial GLI blockade or readily repopulated during recovery, and were poised to regenerate taste buds once Hedgehog signaling was restored, with innervation and papilla connective tissue elements in place. Our data argue that Hedgehog signaling is essential for adult tongue tissue maintenance and that taste papilla epithelial cells represent the key targets for physiologic Hedgehog-dependent regulation of taste organ homeostasis. Because disruption of GLI transcriptional activity in taste papilla epithelium is sufficient to drive taste organ loss, similar to pharmacologic Hedgehog pathway inhibition, the findings suggest that taste alterations in cancer patients using systemic Hedgehog pathway inhibitors result principally from interruption of signaling activity in taste papillae.</p></div

Distinct mechanisms for sebaceous gland self-renewal and regeneration provide durability in response to injury

Summary: Sebaceous glands (SGs) release oils that protect our skin, but how these glands respond to injury has not been previously examined. Here, we report that SGs are largely self-renewed by dedicated stem cell pools during homeostasis. Using targeted single-cell RNA sequencing, we uncovered both direct and indirect paths by which resident SG progenitors ordinarily differentiate into sebocytes, including transit through a Krt5+PPARγ+ transitional basal cell state. Upon skin injury, however, SG progenitors depart their niche, reepithelialize the wound, and are replaced by hair-follicle-derived stem cells. Furthermore, following targeted genetic ablation of >99% of SGs from dorsal skin, these glands unexpectedly regenerate within weeks. This regenerative process is mediated by alternative stem cells originating from the hair follicle bulge, is dependent upon FGFR2 signaling, and can be accelerated by inducing hair growth. Altogether, our studies demonstrate that stem cell plasticity promotes SG durability following injury

Innervation to fungiform papillae and taste buds is retained in epithelial HH/GLI suppression models.

<p><b>A,C,E,G. Chorda/Lingual</b>: K8 immunostaining to label taste bud cells and neurofilament (NF) to label fibers of the chorda tympani/lingual nerve innervation to FP and TB. <b>A</b>. In Control the Chorda/lingual innervation is throughout the FP core and forms a dense ‘basket’ under the TB at the apex of the papilla core. With HH/GLI suppression at specified time points in <i>K5GliR</i> (<b>C</b>), <i>epiGliR</i> (<b>E</b>), and <i>Gli2cKO</i> (<b>G</b>) mice, NF-positive fibers are retained in the FP even though papillae are of atypical morphology and TBs are lost (E) or much reduced (G). At the illustrated time points in all models there are substantial morphological effects, as seen in Figs <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1006442#pgen.1006442.g001" target="_blank">1</a> and <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1006442#pgen.1006442.g002" target="_blank">2</a>. <b>B,D,F,H</b>. <b>Chorda tympani</b>: K8 immunostaining to label taste bud cells and P2X3 to label fibers of the chorda tympani nerve innervation to FP and TB. <b>B</b>. In Control for Chorda tympani innervation the P2X3-positive label is within fibers in the papilla core (arrow) and within the TB. With HH/GLI suppression at specified time points in <i>K5GliR</i> (<b>D</b>), <i>epiGliR</i> (<b>F</b>), and <i>Gli2cKO</i> (<b>H</b>) mice, P2X3-positive fibers (arrows) are retained in the FP and TB cells even though papillae are of atypical morphology and TBs are lost (F) or much reduced (H). Scale bar in H applies to all panels. * in H indicate areas of nonspecific staining in the surface epithelial cells.</p