含SrCaP涂层镁合金ZK60对小鼠前成骨细胞功能的影响

目的探讨含锶钙磷（SrCaP）涂层镁合金ZK60对小鼠前成骨细胞黏附、增殖和成骨分化等功能的影响。方法制备含SrCaP涂层的镁合金ZK60材料,以不含SrCaP涂层的ZK60和钛合金材料作为对照,扫描电镜观察材料表面的超微结构;以小鼠MC3T3-E1细胞为对象,扫描电镜、荧光显微镜、MTT法、p-NPP法等观察上述材料对细胞黏附、增殖和成骨分化的影响。结果扫描电镜可见含SrCaP涂层镁合金ZK60表面的粗糙多孔结构。与ZK60组相比,前成骨细胞在该材料上铺展面积更大,黏附更好;死活细胞染色显示培养24 h时SrCaP-ZK60组活细胞数最多;浸提液培养5 d时SrCaP涂层镁合金组细胞增殖显著高于钛合金组（P＜0.05）;培养7 d后,SrCaP涂层镁合金表面成骨细胞碱性磷酸酶表达显著高于ZK60组及钛合金组（P＜0.05）。结论含SrCaP涂层镁合金ZK60具有良好的促成骨细胞黏附、增殖和成骨分化作用。     

黄芩素通过BMP-2/Smad通路促进MC3T3-E1成骨作用的实验研究

目的 探讨黄芩素（BAI）对小鼠胚胎成骨细胞前体细胞（MC3T3-E1）成骨分化的作用及其分子机制。方法 将MC3T3-E1分为对照组（正常培养）和BAI组（以Baicalein处理）,在成骨分化条件培养下采用CCK-8检测BAI对MC3T3-E1细胞增殖的影响;分别以碱性磷酸酶染色（ALP）、茜素红染色（ARS）检测MC3T3-E1细胞成骨分化水平与矿化能力,实时荧光定量PCR检测成骨标志基因ALP、COL1A1、RUNX2、OSX的mRNA表达水平,通过免疫印迹法（Western-blot）检测MC3T3-E1细胞中BMP-2、Smad1、p-Smad1蛋白表达水平,通过免疫荧光技术（IF）检测RUNX2、COL1A1表达水平。结果 与对照组比较,BAI干预1 d后发现,BAI组COL1A1（P<0.001）、RUNX2（P <0.05）、OSX（P <0.05） mRNA表达水平在成骨分化中表达上升;干预3 d后发现,与对照组比较,BAI组ALP（P <0.05）、RUNX2（P <0.001）mRNA表达上升;干预7 d后发现,与对照组比较,BAI组COL1A1（P <0.05）mRNA表达水平较对照组上升,BMP-2、p-Smad1/Smad1蛋白表达水平上升（P <0.05）。免疫荧光中成骨标志蛋白RUNX2、COL1A1表达增多（P <0.05）。结论 BAI可通过激活BMP-2/Smad通路促进MC3T3-E1成骨分化。     

痩素对小鼠成骨细胞MC3T3-E1增殖及OPG/RANKL mRNA表达的影响

目的初步探讨瘦素对小鼠成骨细胞MC3T3-E1细胞增殖及骨保护蛋白、核因子κB激活受体配体mRNA表达的影响。方法以小鼠成骨细胞MC3T3-E1为体外实验模型,用MTT法检测瘦素作用MC3T3-E1细胞后的增殖情况,RT-PCR方法检测OPG、RANKL mRNA表达。结果瘦素（10、20、40、80和160ng.mL-1）作用于MC3T3-E1细胞24h后,可促进其增殖,OD值显著增加（P〈0.01）,增加骨保护蛋白mRNA表达,同时降低核因子κB激活受体配体mRNA表达,且呈浓度依赖性。结论瘦素促进MC3T3-E1细胞增殖,同时通过调节骨保护蛋白mRNA和核因子κB激活受体配体mRNA的表达,从而促进骨形成,抑制骨吸收。     

辐射对成骨细胞系MC3T3-E1细胞增殖和功能基因表达的影响

目的为了深入了解辐射对成骨细胞的影响,探讨成骨细胞系MC3T3-E1细胞受到辐射后的功能变化。方法将MC3T3-E1细胞体外培养,诱导成骨前体细胞和成骨细胞,经137Csγ射线照射后,用MTT法分析细胞的存活率,用实时定量PCR方法分析ALP、Run X2和M-CSF基因的mRNA表达。结果 MTT实验表明,随照射剂量增加,正常MC3T3-E1细胞生长率明显下降,而经过诱导分化的MC3T3-E1细胞生长率变化越来越不明显。实时定量PCR实验结果表明,经过137Csγ射线照射后,MC3T3-E1细胞的ALP,Run X2和M-CSF基因的mRNA表达出现明显的降低;经过诱导分化为成骨前体细胞的,ALP,Run X2和M-CSF基因的mRNA表达与相应的正常组相比没有明显的规律变化;经过诱导进一步分化成为成骨细胞的,ALP和Run X2表达下降,M-CSF表达呈现升高趋势。结论辐射抑制早期成骨细胞的增殖、发育和分化。随着成骨细胞的分化,辐射对成骨细胞的增殖和生长发育影响减小,但是对成骨细胞发挥调节破骨细胞功能的作用并没有减少。     

芍药苷促进小鼠成骨分化抗骨质疏松作用的实验研究

目的 探讨芍药苷对MC3T3-E1成骨细胞分化以及小鼠骨质疏松模型的影响。 方法 体外细胞实验分为对照组、不同剂量芍药苷干预组。通过CCK-8法检测芍药苷对MC3T3-E1成骨细胞活力的影响;采用碱性磷酸酶（ALP）染色以及活性检测芍药苷促进MC3T3-E1成骨分化能力;通过茜素红染色检测芍药苷促矿化能力;运用荧光定量PCR、Western blot检测Runx2、OPG、RANKL、Col1α1的mRNA以及蛋白表达情况。选取8周龄C57BL/6小鼠24只,分为假手术组、骨质疏松模型组、药物干预组。选取各小鼠左侧股骨远端以及胫骨近端的区域进行苏木素-伊红（HE）染色、Runx2免疫组织化学以及micro-CT扫描。 结果 中、高剂量芍药苷干预组可以促进MC3T3-E1细胞ALP的活性（P<0.05）;高剂量芍药苷能够促进MC3T3-E1细胞的矿化能力（P<0.01）;同时中、高剂量能够促进OPG、Runx2蛋白的表达（P<0.05）,抑制RANKL的表达（P<0.05）。与假手术组比较,OVX组骨微结构破坏明显,Runx2蛋白表达显著减少（P<0.01）;芍药苷干预后骨质疏松模型小鼠骨小梁数量以及厚度显著增加（P<0.01）,骨小梁间隔减少明显（P<0.01）,Runx2蛋白提升明显（P<0.01）。 结论 芍药苷能够促进成骨细胞的分化,上调成骨分化基因,改善骨质疏松模型小鼠的骨微结构,具有抗骨质疏松治疗的潜在价值。     

Pluronic F-127表面修饰生物衍生骨的体外实验研究

目的：探讨成骨细胞复合PluronicF-127表面修饰生物衍生骨的三维培养，对成骨细胞活力及功能表达的影响。方法：将新鲜猪肋骨加工制成生物生骨，应用PluronicF-127对生物衍生骨进行表面修饰，然后体外复合第3代成骨细胞三维培养，实验为A、B和C组，A组为单纯生物衍生骨复合成骨细胞组，B组为PluronicF-127表面修饰生物衍生骨复合成骨细胞组，C组为单纯成骨细胞组，应用倒置相差显微镜和扫描电镜对各组成骨细胞生长及黏附进行观察，并对其细胞活力碱性磷酸酶（ALP）活性进行检测，结果：B组成骨细胞在支架材料上黏附，伸展及生长良好，成骨细胞活力和ALP活性表达与A组成骨细胞比较均无统计学意义（P＞0．05）；A、B组与C组比较，成骨细胞活性和ALP活性均明显降低，有统计学意义（P＜0．01）。结论：生物衍生骨经PluronicF-127表面修饰后具有良好的细胞相容性，可作为负载生物活性分子的载体修饰生物衍生骨。     

负载丹酚酸B的破骨前体细胞膜纳米颗粒对成骨细胞和破骨细胞分化的影响

目的 通过制备破骨前体细胞膜纳米颗粒（nanoparticles，NPs）负载丹酚酸B（salvianolic acid，SalB），构建载药纳米颗粒SalB-NPs，观察其对破骨细胞及成骨细胞分化的影响。方法 采用超声裂解、挤膜的方法制备NPs，并将NPs与SalB共孵育后，使用200 nm聚碳酸酯膜挤出，获得SalB-NPs。在诱导小鼠原代破骨细胞分化和成骨前体细胞（MC3T3-E1）成骨分化的过程中，按照处理方式不同，分为对照组、SalB组、SalB-NPs组。采用透射电镜、纳米粒度及ZETA电位仪和Western Blot对材料进行表征，采用噻唑蓝检测试剂盒检测材料对RAW 264.7和MC3T3-E1细胞活力的影响，采用高效液相色谱法检测SalB的释放率和装载率。采用抗酒石酸酸性磷酸酶（TRAP）染色评价破骨细胞分化能力，通过碱性磷酸酶（ALP）染色和茜素红染色评估成骨分化能力，采用Real time-PCR检测破骨细胞分化及成骨分化相关基因表达水平。结果 制备的纳米颗粒直径在200 nm左右，同时表达RANK蛋白。TRAP染色显示SalB-NPs显著抑制破骨细胞的形成，下调破骨分化相关基因水平，与对照组和SalB组相比，差异有统计学意义（P＜0.05）。使用成骨诱导培养基诱导MC3T3-E1细胞成骨分化，14 d ALP染色和21 d茜素红染色均显示SalB-NPs组ALP活性和钙盐沉积量较SalB组明显增加，差异有统计学意义（P＜0.05）。结论 SalB-NPs体外发挥促进成骨分化、抑制破骨细胞形成双重功效，作为骨质疏松的治疗药物开发，有很好的应用前景，未来仍需在骨质疏松模型动物进一步验证其治疗效果。     

黄芪多糖对MC3T3-E1细胞增殖及成骨分化的影响

目的 分析黄芪多糖（AP）对小鼠成骨细胞系MC3T3-E1的成骨分化作用机制。 方法 MC3T3-E1细胞经成骨诱导后分别加入浓度为0、5、10 μmol/L 的AP进行干预,持续1、3、5、7 d后使用MTT法观察AP对细胞增殖的影响;干预14 d后,通过ALP及茜素红染色观察AP的促成骨分化作用;成骨相关mRNA表达水平经实时荧光定量PCR测定,其中包括Runt相关转录因子2(Runx2)、β-连环蛋白(β-catenin)、骨钙素（osteocalcin）、I型胶原蛋白（collagen I）;并使用Western blot法检测β-catenin、osteocalcin、Runx2蛋白表达水平,以及免疫荧光检测β-catenin的核易位情况。 结果 加入5、10 μmol/L 的AP后可有效促进MC3T3-E1增殖,且药物浓度越高效果越明显;同时AP亦可提高ALP、茜素红染色的阳性率,以及β-catenin、osteocalcin、Runx2、collagen I mRNA的表达水平（P<0.05）;Western blot结果也显示AP可有效促进β-catenin、osteocalcin、Runx2蛋白表达（P<0.05）,以及促进β-catenin入核。 结论 AP可促进MC3T3-E1细胞增殖及成骨分化,机制可能涉及促进相关成骨标志物表达以及β-catenin入核。     

高铁培养环境对小鼠前成骨细胞MC3T3-E1增殖、分化的影响

目的 观察高铁培养环境下小鼠前成骨样细胞MC3T3-E1增殖、分化指标的变化趋势,探讨铁离子对 成骨细胞增殖、分化的影响。方法 小鼠前成骨样细胞MC3T3-E1在37℃条件下体外培养,在10mmol/Lβ-甘 油磷酸和50μg /mL抗坏血酸的诱导分化的作用下,分化为成骨细胞,同时用不同浓度(50、100、 200μmol/L)枸橼酸铁铵(FAC)干预,用MTT法检测细胞的增殖活性,RT-PCR法检测成骨细胞分化基因成骨 相关转录因子(Runx2) 、锌指结构转录因子(Osterix) 、骨唾液酸蛋白(BSP)和骨钙素(OC)的表达,碱性 磷酸酶(ALP)活性试剂盒检测细胞碱性磷酸酶活性。结果 MC3T3-E1细胞的增殖活性、成骨分化相关基因的 表达以及ALP水平随FAC干预浓度的增加呈剂量依赖性降低(P<0.05)。结论 高铁培养环境可明显抑制小鼠 前成骨样细胞MC3T3-E1的增殖和分化。     

续苓健骨汤含药血清对MC3T3-E1细胞分化及增殖的影响

目的探讨续苓健骨汤含药血清对MC3T3-E1成骨细胞分化及增殖的影响。方法制备续苓健骨汤含药血清,实验分为空白对照组、含药血清低剂量组、中剂量组和高剂量组。采用CCK-8法和流式细胞术检测续苓健骨汤含药血清对MC3T3-E1细胞增殖和细胞周期的影响;碱性磷酸酶(ALP)活性测定MC3T3-E1细胞的成骨分化能力;茜素红染色检测MC3T3-E1细胞的矿化能力;实时荧光定量PCR检测成骨分化基因Runx2、OC、Bmp2、Col1a1mRNA水平。结果与空白对照组比较,中、高剂量续苓健骨汤含药血清能促进MC3T3-E1细胞增殖、S期细胞比率和细胞增殖指数,并且呈现一定的剂量依赖性;同时中高剂量续苓健骨汤含药血清组能明显提高MC3T3-E1细胞ALP活性(P0.01)和钙化能力(P0.01),促进Runx2、OC、Bmp2、Col1a1 mRNA的表达(P0.05)。结论续苓健骨汤含药血清能促进成骨细胞MC3T3-E1的增殖,并通过上调骨形成相关基因Runx2、OC、BMP2、Col1a1的表达水平,提高MC3T3-E1细胞的成骨能力。     

pcDNA3-hBMP2转染对成纤维细胞 生物学性状的影响

目的 探讨人BMP2基因转染对成纤维细胞NIH3T3生物学性状的影响。方法 构建重组真核表达载体pcDNA3-hBMP2,并在脂质体介导下,将其导入NIH3T3成纤维细胞,通过G418筛选获得阳性克隆,用细胞原位杂交和免疫组织化学方法检测hBMP2基因在NIH3T3成纤维细胞内的表达情况;MTT法和FCM检测pcDNA3-hBMP2转染pcDNA3-hBMP2后成纤维细胞超微结构的改变,碱性磷酸酶的检测观察转染pcDNA3-hBMP2后成纤维细胞向成骨细胞分化情况。结果 转染pcvDNA3-hBMP2后的NIH3T3细胞内有大量hBMP2mRNA的转录及其蛋白的表达;转染pcDNA3-hBMP2对成纤维细胞增殖和细胞周期无影响;转染pcDNA3-hBMP2后的成纤维细胞超微结构可见粗面内质网丰富,囊腔扩张明显其内充满中等电子密度的蛋白分泌物;碱性磷酸酶活性显著上升。结论 pcDNA3-hBMP2转染对成纤维细胞NIH3T3增殖和细胞周期无影响。转染后的成纤维细胞不仅可形成BMP2,而且具有向成骨细胞系分化的特性。     

Choledochal cysts: Part 3 of 3: Management

Much about the etiology, pathophysiology, natural course and optimal treatment of cystic disease of the biliary tree remains under debate. Gastroenterologists, surgeons and radiologists alike still strive to optimize their roles in the management of choledochal cysts. To that end, much has been written about this disease entity, and the purpose of this 3-part review is to organize the available literature and present the various theories currently argued by the experts. In part 3, we discuss the management of choledochal cysts, thus completing our comprehensive review.     

H3K4m3和H3K9m3修饰对胰岛组织特异性基因表达的影响

目的 通过比较不同细胞类型之间胰腺十二指肠同源盒1(Pdx-1)、配对盒基因4(Pax4)、MafA(mast cell function associated antigen)和Nkx6.1等胰岛组织特异性基因其转录起始区的H3K4m3和H3K9m3修饰的差异,探讨H3K4m3和H3K9m3修饰对胰岛组织特异性基因表达的作用.方法 采用染色质免疫共沉淀一实时定量聚合酶链反应(PCR)法检测小鼠胚胎干细胞(mES,1×10~7)、小鼠成纤维细胞株NIH3T3细胞(1×10~7)和小鼠β细胞株NIT-1细胞(1×10~7)三者中的胰岛组织特异性基因、Oct4基因和MLH1基因转录起始区H3K4m3和H3K9m3修饰的状况.同时采用实时定量逆转录(RT)-PCR检测上述3种细胞各基因mRNA表达水平.分析H3K4m3和H3K9m3修饰改变与基因表达之间的关系.结果 NIT-1细胞中Pdx-1、Pax4、MafA、Nkx6.1等胰岛组织特异性基因转录起始区的H3K4m的修饰水平分别为:(4.84±0.05)%、(9.91±1.33)%、(10.64±0.87)%、(0.23±0.03)%,与mES细胞比较明显增高(P<0.05),基因表达;NIH3T3细胞中Pdx-1、Pax4、MafA、Nkx6.1等胰岛组织特异性基因转录起始区的H3K9m3的修饰水平分别为:(0.64±0.21)%、(7.04±1.29)%、(0.39±0.10)%、(2.35±0.81)%,与mES细胞比较明显增高(P<0.05),基因不表达.结论 H3K4m3与H3K9m3修饰能相互协调,共同调控胰岛组织特异性基因的表达.     

Overexpression of EIF3S3 promotes cancer cell growth

BACKGROUND: Amplification and overexpression of EIF3S3 gene has been demonstrated in breast and prostate cancer. Here, our goal was to study the effect of EIF3S3 on cell growth. METHODS: The effect of EIF3S3 on growth of NIH 3T3 murine fibroblasts as well as breast (SK-Br-3 and ZR-75-1) and prostate (PC-3 and LNCaP) cancer cell lines was examined by using transfection with inducible pTet-Off system and siRNAs. RESULTS: NIH 3T3 cells with overexpression of EIF3S3 grew significantly faster than cells transfected with empty vector and survived longer when grown in soft agar. The EIF3S3 overexpression was associated with increased fraction of cells in S-phase and with phosphorylation of retinoblastoma (Rb) protein. siRNA treatment inhibited significantly (P = 0.0022) the growth of all breast and prostate cancer cell lines studied. CONCLUSIONS: The results suggest that EIF3S3 regulates cell growth and viability, and that overexpression of the gene may provide growth advantage to the cancer cells.     

Identification of the insulin-regulated interaction of phosphodiesterase 3B with 14-3-3 beta protein

Phosphodiesterase (PDE)-3B, a major PDE isoform in adipocytes, plays a pivotal role in the antilipolytic action of insulin. Insulin-induced phosphorylation and activation of PDE3B is phosphatidylinositol 3-kinase (PI3-K) and Akt dependent, but the precise mechanism of PDE3B activation is not fully understood. We have identified 14-3-3 beta, a critical scaffolding molecule in signal transduction, as a protein that interacts with PDE3B using the yeast two-hybrid system. The interaction between PDE3B and 14-3-3 beta was then confirmed in vitro. The glutathione S-transferase (GST)-tagged 14-3-3 beta interacts with endogenous PDE3B of rat adipocytes, and this interaction is enhanced when adipocytes are treated with insulin. Coimmunoprecipitation experiments reveal that endogenous PDE3B also associates with endogenous 14-3-3 beta in rat adipocytes, and this interaction is enhanced by insulin. Two different PI3-K inhibitors, wortmannin and Ly294002, block this induction, suggesting that PI3-K is required. Synthetic 15 amino acid peptides of rat PDE3B containing phosphorylated Ser-279 or -302 inhibit this interaction, indicating that the insulin-regulated phosphorylation of these serine residues is involved. Because insulin receptor substrate-1 also associates with 14-3-3, the dimeric 14-3-3 beta could function as a scaffolding protein in the activation of PDE3B by insulin.     

SH3BP2 mutations potentiate osteoclastogenesis via PLCγ

To determine the mechanism for the increased osteoclastogenesis in the jaw of cherubism patients with SH3BP2 mutations we evaluated the effect of mutant compared to wild‐type SH3BP2 on activation of osteoclast signaling pathways. Indeed mutant forms of SH3BP2 do induce greater osteoclastogenesis. Heterozygous activating mutations in exon 9 of SH3BP2 have been found in most patients with cherubism, an unusual genetic syndrome characterized by excessive remodeling of the mandible and maxilla due to spontaneous and excessive osteoclastic bone resorption. Here we have investigated the functional consequences of SH3BP2 mutations on sRANKL‐induced osteoclastogenesis in RAW 264.7 pre‐osteoclast cells. sRANKL‐stimulated RAW 264.7 cells were transfected with wild‐type or mutant SH3BP2 plasmids. NFAT‐luciferase and tartrate resistant acid phosphatase (TRAP), a marker of osteoclastic differentiation, levels were evaluated. Western immunoblots were also performed to determine phosphorylation of key proteins involved in the PI‐PLC pathway leading to NFATc1 translocation. Our results indicate that forced expression of mutant forms of SH3BP2, found in cherubism patients, in RAW 264.7 cells induce greater NFAT activity and greater expression of TRAP than forced expression of wild‐type SH3BP2. These findings indicate that missense SH3BP2 mutations cause a gain of protein function. Moreover, over expression of SH3BP2 in RAW 264.7 cells potentiates sRANKL‐stimulated phosphorylation of PLCγ1 and PLCγ2. Our studies demonstrate that cherubism is due to gain‐of‐function mutations in SH3BP2 that stimulate RANKL‐induced activation of PLCγ. The consequent activation of calcineurin and NFAT proteins induces the excessive osteoclastic phenotype of cherubism. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:1425–1430, 2010     

Effects of carboxy-terminal modifications of proteinase 3 (PR3) on the recognition by PR3-ANCA

BACKGROUND: Autoantibodies directed against neutrophil proteinase 3 (PR3-ANCA) from patients with Wegener's granulomatosis and microscopic polyangiitis recognize conformational epitopes of PR3. During maturation of neutrophils, PR3 undergoes amino-terminal and carboxy-terminal processing. In contrast to amino-terminal processing, the effects of carboxy-terminal processing on recognition of PR3 by PR3-ANCA remain unknown. Carboxy-terminally modified or tagged recombinant PR3 (rPR3) molecules may be useful for the refinement of diagnostic assays and for the study of biological processes. METHODS: This study was designed to determine whether 293 cells can be used to express specifically designed carboxy-terminal variants of rPR3, and to evaluate the effects of different carboxy-terminal modifications on the recognition by PR3-ANCA in the capture ELISA. RESULTS: The rPR3-variants secreted into the media supernatants of transfected 293 cells escaped proteolytic processing. Furthermore, in contrast to the effects of amino-terminal pro-peptide deletion on PR3-ANCA binding, carboxy-terminal modifications (deletion and additions) did not significantly affect recognition by PR3-ANCA. CONCLUSIONS: This expression system is ideally suited for the expression of custom-designed carboxy-terminal rPR3 variants, and major conformational effects of carboxy-terminal modifications seem unlikely.     

Actin and microtubule cytoskeletons of the processes of 3D-cultured MC3T3-E1 cells and osteocytes

Cell shape is the most critical determinant of cell function and is potentially influenced by the organization of a cell's cytoskeletal components. It has been reported that three-dimensionally cultured osteoblasts have a morphology that closely resembles that of osteocytes, most notably including formation of processes. We have previously shown the critical differences between cytoskeletal components in osteoblasts and osteocytes in two-dimensional culture. We have now extended that investigation to the cytoskeletal components of 3D-cultured osteoblasts and osteocytes using 3D cultures of the osteoblast cell line, MC3T3-E1, and primary osteocytes grown in collagen gel. Three-dimensional fluorescent image reconstructions for actin, fimbrin, alpha-actinin, myosin, tropomyosin, and microtubules were made using IMARIS software. Actin, fimbrin, alpha-actinin, myosin, and tropomyosin all appeared in the processes of both cell types, but fimbrin and myosin showed differences in their distribution patterns between cell types. Microtubules were limited in distribution to the proximal region of osteocyte processes but extended the entire length of MC3T3-E1 cell processes. Microtubules were essential for the integrity and formation of MC3T3-E1 cell processes, but osteocyte processes were dependent on actin. These results showed that there are significant differences between the actin and microtubule cytoskeletons in the processes of 3D-cultured MC3T3-E1 cells and in the processes of 3D-cultured primary osteocytes. These differences in the cytoskeleton of the processes of 3D-cultured osteoblasts and of osteocyte dendrites suggest that osteoblast processes may have a different functional role than the osteocyte dendritic network. An erratum to this article is available at .