阻遏蛋白β-TrCP在小鼠牙胚不同发育时期的表达与意义

目的观察Sonic hedgehog（shh）信号转导通路的阻遏蛋白β- TrCP在小鼠牙胚发育不同时期的表达情况，探讨β- TrCP在晚期牙胚发育中的作用与意义。方法取不同发育时期的鼠胚、乳鼠鼠头标本，用标记生物素链亲和素LsAB法观察β- TrCP蛋白在不同发育时期牙胚组织的表达情况。结果β- TrCP在胚胎10.5、13.5、14.5、16.5、18.5 d的小鼠牙胚上皮层与间充质层，以及出生后0、3、6 d的小鼠成釉细胞与成牙本质细胞胞浆呈特征性表达。结论β- TrCP在正常发育小鼠牙胚及成釉细胞与成牙本质细胞特征性表达，提示β- TrCP在牙胚发育中维持/限定shh信号通路的正常信号转导具有重要意义。     

Dental follicle cells and cementoblasts induce apoptosis of ameloblast-lineage and Hertwig's epithelial root sheath/epithelial rests of Malassez cells through the Fas-Fas ligand pathway

Hertwig's epithelial root sheath (HERS), epithelial rests of Malassez (ERM) cells, and reduced ameloblasts undergo apoptosis during tooth development. This study examined the effects of dental follicle cells and cementoblasts on the apoptosis of ameloblast-lineage and HERS/ERM cells derived from the enamel organ. We also elucidated the induction pathways and identified the apoptotic pathway involved in this process. Here, we showed terminal deoxynucleotidyl transferase-mediated biotin-dUTP nick-end labeling (TUNEL)-positive HERS cells and reduced ameloblasts near dental follicle cells during tooth development. Co-culturing ameloblast-lineage cell line (ALC) ameloblasts and HERS/ERM cells with either dental follicle cells or OCCM-30 cementoblasts markedly enhanced the apoptosis of ameloblasts and HERS/ERM cells compared with cells cultured alone. However, dental follicle cells and cementoblasts did not modulate the apoptotic responses of co-cultured non-odontogenic MCF10A or KB cells. When ameloblasts + HERS and cementoblasts + dental follicle cells were co-cultured, the expression of Fas ligand (FasL) increased in cementoblasts + dental follicle cells, while the expression of Fas increased in ameloblasts + HERS. Interestingly, recombinant FasL induced ameloblast apoptosis while the cementoblast-induced ameloblast apoptosis was suppressed by the Fas/FasL antagonist Kp7-6. These results suggest that during tooth development, dental follicle cells and cementoblasts induce apoptosis of ameloblast-lineage and HERS/ERM cells through the Fas-FasL pathway, but do not induce the apoptosis of non-odontogenic epithelial cells.     

不同质量浓度氟对大鼠切牙成釉细胞转化生长因子-β1表达的影响

目的研究不同质量浓度氟对大鼠切牙生长过程中转化生长因子-β1（TGF-β1）表达的影响,探讨氟斑牙的发病机制。方法40只Wistar大鼠随机分为3组,建立氟斑牙动物模型。3组分别为低剂量氟组（F-质量浓度60 mg·L-1,13只）、高剂量氟组（F-质量浓度120 mg·L-1,13只）和对照组（蒸馏水,14只）。10周后取材,采用苏木精-伊红（HE）染色和免疫组织化学染色的方法观察氟对大鼠切牙成釉细胞的形态及TGF-β1表达的影响。结果实验组大鼠切牙均出现典型的氟斑牙症状,牙面出现白垩色改变,釉质表面有横纹。HE染色结果显示成釉细胞形态发生改变,细胞排列紊乱,甚至成灶性堆积,可见空泡性变。免疫组织化学染色结果显示TGF-β1在分泌期和成熟期成釉细胞均为强阳性表达,在星网状层、中间层均为阳性表达,在新形成的釉基质中呈阳性表达。2个实验组TGF-β1的表达强度明显低于对照组（P<0.01）,2个实验组之间的差异无统计学意义（P＞0.05）。结论氟可能通过抑制TGF-β1的表达而干扰了成釉细胞的分化和基质分泌,造成釉质发育障碍。     

硒对氟斑牙发生的拮抗作用及其对Beclin1表达的影响

目的 研究硒对小鼠氟斑牙发生的拮抗作用,并检测其对自噬相关基因Beclin1表达的影响。方法 将36只2月龄费城癌症研究所（institute of cancer research, ICR）雄鼠,随机分为3组,每组12只,建立饮水型氟斑牙模型,用亚硒酸钠（Na2SeO3）进行干预,具体分组为： 对照组（ddH2O）、氟化钠组（200mg/L NaF）、硒组（2mg/L Na2SeO3+200mg/L NaF）,喂养8周后,观察氟斑牙发生情况,记录其长度并计算小鼠下颌切牙增长率;分离下颌骨后,进行micro-CT扫描,测量小鼠切牙唇侧硬组织厚度;H-E染色观察成釉细胞的变化,免疫组化方法检测Beclin1的表达。结果 氟化钠组氟斑牙检出率为100%,表现为小鼠切牙白垩色改变;硒组未发现明显氟斑牙症状,形态与色泽介于正常与极轻度之间;micro-CT结果显示,氟化钠组切牙唇侧硬组织厚度比对照组薄,硒组介于两者之间(P<0.01);H-E 结果显示,氟化钠组成釉细胞排列紊乱,极性消失;而对照组与硒拮抗组成釉细胞呈栅栏状,排列整齐规则;免疫组化结果显示,3组中成釉细胞从分泌期到成熟期Beclin1的阳性表达均呈逐渐增强的表达趋势,且Beclin1在氟化钠组表达明显强于正常组,硒组介于两者之间。结论 2mg/L硒离子浓度对氟斑牙的发生有一定拮抗作用;其作用机制可能是通过抑制成釉细胞自噬的发生,进而减轻过量氟对小鼠切牙毒性影响。     

SEM evidence that one ameloblast secretes one keyhole-shaped enamel rod in monkey teeth

Primate enamel is subdivided into inner enamel, having Hunter–Schreger bands, and outer enamel with all rods parallel to each other. Outer inter-rod enamel may surround each rod, lie between rows of rods, or be absent, as in the 'keyhole pattern', which is composed entirely of rods. One theory on the formation of the 'keyhole' pattern overlays the hexagonal cross-sectional shape of four or more ameloblasts over the keyhole shape of the enamel rod. This ignores the likelihood that Tomes processes have a different shape from the cell body, and also ignores the observation that paths of enamel rods sometimes diverge. Scanning electron microscopy (SEM) revealed the keyhole shape of the forming face of monkey enamel. These forming rods were arranged in stepped rows with the head regions in each row separated by the tails of the preceding row. Consequently, each forming face of a rod was surrounded on three sides by previously formed enamel. The apical surface of the Tomes process was shaped exactly like the forming rod face, permitting direct apposition of one rod and one Tomes process. The conclusion was that, in the monkey, each rod of the keyhole enamel configuration is produced by one ameloblast.     

Tooth Crown Morphogenesis and Cytodifferentiations: Candid Questions and Critical Comments

Teeth are probably meristic units and crown morphogenesis leads to tooth specific distribution of functional cells. Since heterodonty is derived from homodonty, one way to understand tooth morphogenesis would be to unravel the involved phenomena in homodont species and then to characterize the “put up job” of evolution leading to species specific dentitions with particular functional abilities. Interaction of paleontologists and developmental biologists should be initiated. My naive “developmental” point of view will illustrate only one facet of mouse tooth morphogenesis and cytodifferentiation. The main concern will be to try to discriminate between known facts and speculations, between hypotheses and anticipated or deduced certitudes, to call attention to conflicting data, to suggest some further investigations and to advocate the point of view that molecular interpretations should be founded on indisputable morphological data.     

Overexpression of transforming growth factor-beta1 in teeth results in detachment of ameloblasts and enamel defects

Transforming growth factor-beta1 (TGF-beta1) is a key regulator of many cellular processes, including cell adhesion, the immune response and synthesis of extracellular matrix proteins. In the present study, we report the characterization of enamel defects in a transgenic mouse model overexpressing TGF-beta1 in odontoblasts and ameloblasts, its expression being driven by the promoter sequences of the dentin sialophosphoprotein gene. As reported earlier, these mice develop distinct dentin defects similar to those seen in human dentin dysplasia and dentinogenesis imperfecta. A further detailed examination of enamel in these mice revealed that from the early secretory stage, ameloblasts began to detach from dentin to form cyst-like structures. A soft X-ray analysis revealed that this cyst-like structure had a disorganized and partially mineralized matrix with an abnormal mineralization pattern and a globular appearance. In the molars, the enamel was not only pitted and hypoplastic, but enamel rods were completely lost. Thus, altered TGF-beta1 expression in the tooth seems to trigger detachment of ameloblasts and abnormal secretion and deposition of minerals in the cyst-like structures adjoining the dentin. We speculate that the altered expression of TGF-beta1 in teeth impacts the adhesion process of ameloblasts to dentin.