Wnt8a and Wnt3a cooperate in the axial stem cell niche to promote mammalian body axis extension

Background: Vertebrate body axis extension occurs in a head‐to‐tail direction from a caudal progenitor zone that responds to interacting signals. Wnt/β‐catenin signaling is critical for generation of paraxial mesoderm, somite formation, and maintenance of the axial stem cell pool. Body axis extension requires Wnt8a in lower vertebrates, but in mammals Wnt3a is required, although the anterior trunk develops in the absence of Wnt3a. Results: We examined mouse Wnt8a^–/– and Wnt3a^–/– single and double mutants to explore whether mammalian Wnt8a contributes to body axis extension and to determine whether a posterior growth function for Wnt8a is conserved throughout the vertebrate lineage. We find that caudal Wnt8a is expressed only during early somite stages and is required for normal development of the anterior trunk in the absence of Wnt3a. During this time, we show that Wnt8a and Wnt3a cooperate to maintain Fgf8 expression and prevent premature Sox2 up‐regulation in the axial stem cell niche, critical for posterior growth. Similar to Fgf8, Wnt8a requires retinoic acid (RA) signaling to restrict its caudal expression boundary and possesses an upstream RA response element that binds RA receptors. Conclusions: These findings provide new insight into interaction of caudal Wnt‐FGF‐RA signals required for body axis extension. Developmental Dynamics 244:797–807, 2015. © 2015 Wiley Periodicals, Inc.     

Rare LRP6 Variants Identified in Spina Bifida Patients

Several single‐nucleotide variants (SNVs) in low‐density lipoprotein receptor‐related protein 6 (Lrp6) cause neural tube defects (NTDs) in mice. We therefore examined LRP6 in 192 unrelated infants from California with the NTD, spina bifida, and found four heterozygous missense SNVs, three of which were predicted to be deleterious, among NTD cases and not in 190 ethnically matched nonmalformed controls. Parents and siblings could not be tested because of the study design. Like Crooked tail and Ringleschwanz mouse variants, the p.Tyr544Cys Lrp6 protein failed to bind the chaperone protein mesoderm development and impaired Lrp6 subcellular localization to the plasma membrane of MDCK II cells. Only the p.Tyr544Cys Lrp6 variant downregulated canonical Wnt signaling in a TopFlash luciferase reporter in vitro assay. In contrast, three Lrp6 mutants (p.Ala3Val, p.Tyr544Cys, and p.Arg1574Leu) increased noncanonical Wnt/planar cell polarity (PCP) signaling in an Ap1‐luciferase assay. Thus, LRP6 variants outside of YWTD repeats could potentially predispose embryos to NTDs, whereas Lrp6 modulation of Wnt/PCP signaling would be more essential than its canonical pathway role in neural tube closure.     

Silicone rubber membrane with specific pore size enhances wound regeneration

A porous structure is critically important for wound dressing or tissue engineering scaffolds. However, the influence of the pore sizes on cell proliferation, tissue regeneration and the underlying mechanism remains unclear. In this study, silicone rubber membranes with different pore sizes were prepared using certain constituents of liquid silicone rubber precursor/liquid paraffin/hexane based on our previous studies. It was found that pore size had a significant impact on cell proliferation and wound healing. The CCK8 analysis revealed that the membrane with a certain pore size (110.47 μm, middle pore membrane, MPM) was suitable for cell proliferation compared with the membranes with other pore sizes (218.03 μm, large pore membrane, LPM; 5.27 μm, small pore membrane, SPM; non‐porous membrane, NPM). Further studies demonstrated that the MPM promoted cell proliferation via activating the Wnt/β‐catenin signalling pathway. More importantly, wound healing experiments showed that 7 days post‐wounding, the rate of wound healing was 89.25% with the MPM, which was significantly higher than with LPM, SPM or NPM. The in vivo data indicated that wound healing was accelerated by treatment with a silicone rubber membrane with a pore size of 110.47 μm. Our results strongly suggest that different pore structures might affect cell proliferation and wound healing and that a silicone rubber membrane with a specific pore size could potentially be used as a promising wound dressing. Copyright © 2017 John Wiley & Sons, Ltd.     

CCN家族在Wnt3a抑制多潜能干细胞C3H10T1/2细胞脂肪分化中的作用

目的:探究CCN家族在Wnt3a抑制鼠胚胎间充质干细胞C3H10T1/2细胞脂肪分化过程中的作用,为干预肥胖提供新思路。方法:用激素混合物(IDM)诱导多潜能干细胞C3H10T1/2向脂肪细胞分化,观察Wnt3a对脂肪分化的抑制作用及脂肪细胞分化过程CCN家族的作用。实时定量RT-PCR分析CCN家族和PPARγ基因表达,用油红O染色观察脂肪分化程度,免疫荧光观察脂肪分化过程中细胞间基质的变化。结果:Wnt3a抑制由IDM诱导的脂肪细胞分化。分子水平上,Wnt3a显著抑制脂肪分化关键因子PPARγ的基因和蛋白表达;而IDM诱导CCN家族,尤其是CCN5基因表达的丧失,可部分被Wnt3a所逆转。结论:Wnt3a抑制C3H10T1/2的脂肪分化,至少部分归结于其对由IDM诱导的CCN家族,尤其是CCN5表达丧失的逆转。     

Rapamycin attenuates articular cartilage degeneration by inhibiting β-catenin in a murine model of osteoarthritis

Purpose: To investigate whether systemic injection of rapamycin attenuates articular cartilage degeneration by inhibiting β-catenin in a murine model of osteoarthritis (OA).

Materials and methods: Ten-week-old male C57BL/6j wild-type (WT) mice and SOST-knockout (SOST^?/?) mice were randomized to a sham group, a vehicle-treated group, and a rapamycin-treated group. Mice in the vehicle-treated group underwent destabilizing of the medial meniscus (DMM) in the right knee, and were then treated with vehicle. Mice in the rapamycin treatment group underwent DMM and were treated with rapamycin. Safranin O-Fast green staining and Osteoarthritis Research Society International (OARSI) modified Mankin score were used to evaluate the histopathological features of the articular cartilage in the knee. The expression of light chain 3 (LC3) was evaluated by immunofluorescence, whereas the expression of ATG5, matrix metallopeptidase 13 (MMP-13), vascular endothelial growth factor (VEGF), sclerostin, and β-catenin were evaluated by immunohistochemistry. TUNEL staining was used to determine apoptosis of chondrocytes.

Results: In vehicle-treated mice when compared with mice in the sham group, the OARSI scores, expression of MMP-13, VEGF, sclerostin, β-catenin, and chondrocyte apoptosis were significantly increased, whereas the expression of LC3 and ATG5 were significantly decreased. A systemic injection of rapamycin activated chondrocyte autophagy, which increased the expression of LC3 and ATG-5, and reduced OARSI scores, the expression of β-catenin, MMP-13, and VEGF, and chondrocyte apoptosis in rapamycin treated mice when compared with vehicle-treated mice.

Conclusions: Systemic injection of rapamycin attenuated articular cartilage degeneration by inhibiting β-catenin in a murine model of OA.     

Over- and Ectopic Expression of Wnt3 Causes Progressive Loss of Ameloblasts in Postnatal Mouse Incisor Teeth

Intercellular signaling is essential for the development of teeth during embryogenesis and in maintenance of the continuously growing incisor teeth in postnatal rodents. WNT intercellular signaling molecules have been implicated in the regulation of tooth development, and the Wnt3 gene shows specific expression in the enamel knot at the cap stage. We demonstrate here that Wnt3 also is expressed in specific epithelial cell layers in postnatal incisor teeth. To begin to delineate the functions of Wnt3 in developing and postnatal teeth, we determined the effects of over- and ectopic expression of Wnt3 in the tooth epithelium of mice carrying a keratin 14- Wnt3 transgene. Expression of the transgene caused a progressive loss of ameloblasts from postnatal lower incisor teeth. Loss of ameloblasts may be due to defective proliferation or differentiation of ameloblast precursors, progressive apoptosis of ameloblasts, or loss of ameloblast stem cells.     

Fgf20 governs formation of primary and secondary dermal condensations in developing hair follicles

In hair follicle development, a placode-derived signal is believed to induce formation of the dermal condensation, an essential component of ectodermal organs. However, the identity of this signal is unknown. Furthermore, although induction and patterning of hair follicles are intimately linked, it is not known whether the mesenchymal condensation is necessary for inducing the initial epithelial pattern. Here, we show that fibroblast growth factor 20 (Fgf20) is expressed in hair placodes and is induced by and functions downstream from epithelial ectodysplasin (Eda)/Edar and Wnt/β-Catenin signaling to initiate formation of the underlying dermal condensation. Fgf20 governs formation of primary and secondary dermal condensations in developing hair follicles and subsequent formation of guard, awl, and auchene hairs. Although primary dermal condensations are absent in Fgf20 mutant mice, a regular array of hair placodes is formed, demonstrating that the epithelial patterning process is independent of known histological and molecular markers of underlying mesenchymal patterns during the initial stages of hair follicle development.