No abstract

Zebrafish regenerate their fins via the formation of a population of progenitor cells, the blastema. Wnt/β-catenin signaling is essential for blastemal cell proliferation and patterning of the overlying epidermis. Yet, we find that β-catenin signaling is neither active in the epidermis nor the majority of the proliferative blastemal cells. Rather, tissue-specific pathway interference indicates that Wnt signaling in the nonproliferative distal blastema is required for cell proliferation in the proximal blastema, and signaling in cells lining the osteoblasts directs osteoblast differentiation. Thus, Wnt signaling regulates epidermal patterning, blastemal cell proliferation, and osteoblast maturation indirectly via secondary signals. Gene expression profiling, chromatin immunoprecipitation, and functional rescue experiments suggest that Wnt/β-catenin signaling acts through Fgf and Bmp signaling to control epidermal patterning, whereas retinoic acid and Hedgehog signals mediate its effects on blastemal cell proliferation. We propose that Wnt signaling orchestrates fin regeneration by defining organizing centers that instruct cellular behaviors of adjacent tissues.

Wnt/β-catenin signaling plays critical roles during embryogenesis, tissue homeostasis, and regeneration. How Wnt-receptor complex activity is regulated is not yet fully understood. Here, we identify the Ly6 family protein LY6/PLAUR domain-containing 6 (Lypd6) as a positive feedback regulator of Wnt/β-catenin signaling. lypd6 enhances Wnt signaling in zebrafish and Xenopus embryos and in mammalian cells, and it is required for wnt8-mediated patterning of the mesoderm and neuroectoderm during zebrafish gastrulation. Lypd6 is GPI anchored to the plasma membrane and physically interacts with the Wnt receptor Frizzled8 and the coreceptor Lrp6. Biophysical and biochemical evidence indicates that Lypd6 preferentially localizes to raft membrane domains, where Lrp6 is phosphorylated upon Wnt stimulation. lypd6 knockdown or mislocalization of the Lypd6 protein to nonraft membrane domains shifts Lrp6 phosphorylation to these domains and inhibits Wnt signaling. Thus, Lypd6 appears to control Lrp6 activation specifically in membrane rafts, which is essential for downstream signaling.

Key Points• UTX regulates migration and hematopoiesis.• Female UTX-KO mice show key features of myelodysplastic syndrome with chromosomal instability.Regulated migration of hematopoietic stem cells is fundamental for hematopoiesis. The molecular mechanisms underlying stem cell trafficking are poorly defined. Based on a short hairpin RNA library and stromal cell-derived factor-1 (SDF-1) migration screening assay, we identified the histone 3 lysine 27 demethylase UTX (Kdm6a) as a novel regulator for hematopoietic cell migration. Using hematopoietic stem and progenitor cells from our conditional UTX knockout (KO) mice, we were able to confirm the regulatory function of UTX on cell migration. Moreover, adult female conditional UTX KO mice displayed myelodysplasia and splenic erythropoiesis, whereas UTX KO males showed no phenotype. During development, all UTX KO female and a portion of UTX KO male embryos developed a cardiac defect, cranioschisis, and died in utero. Therefore, UTY, the male homolog of UTX, can compensate for UTX in adults and partially during development. Additionally, we found that UTX knockdown in zebrafish significantly impairs SDF-1/CXCR4-dependent migration of primordial germ cells. Our data suggest that UTX is a critical regulator for stem cell migration and hematopoiesis. (Blood. 2013;121(13):2462-2473

The diffusion dynamics of lipids and GPI-anchored proteins is investigated using superresolution STED microscopy combined with single-molecule fluorescence correlation spectroscopy in the cellular membranes. The actin cytoskeleton is shown to play an essential role in the diffusion characteristics of molecules.