Wang Y H, Upholt W B, Sharpe P T, Kollar E J, Mina M
Department of BioStructure and Function, School of Dental Medicine, University of Connecticut Health Center, Farmington 06030, USA.
Dev Dyn. 1998 Dec;213(4):386-97. doi: 10.1002/(SICI)1097-0177(199812)213:4<386::AID-AJA4>3.0.CO;2-2.
Previous observations have shown that, during the initiation phase of odontogenesis, signals from mouse odontogenic epithelium can elicit teeth in non-odontogenic but neural crest-derived mesenchyme isolated from ectopic sites including chick mandibular mesenchyme. In the present study the formation of ectopic tooth buds and dental mesenchyme in chick mandibular mesenchyme was examined using heterospecific recombinations between E11 mouse odontogenic epithelium and stage 23 chick lateral mandibular mesenchyme. Both morphological criteria and chick-specific probes for Msx-1, Msx-2, and Bmp-4 mRNAs were used as markers for early dental mesenchyme. Our results demonstrated that interactions of mouse odontogenic epithelium with chick mandibular mesenchyme induce early changes in the chick mandibular mesenchyme including the appearance of a translucent zone, cell proliferation, and induction of expression of Msx-1, Msx-2, and Bmp-4, which have been shown to be associated with the formation of dental mesenchyme. In addition, tooth bud-like structures that resemble E13 tooth buds in vivo both morphologically and in their patterns of gene expression formed after 6 days in the heterospecific recombinations. The tooth bud-like structures consist of invaginated mouse mandibular epithelium and condensed chick mandibular mesenchyme expressing high levels of Msx-1 and Bmp-4, but undetectable levels of Msx-2. Unlike the induction of Msx-1, Msx-2, and Bmp-4 in the underlying mesenchyme, which is specific for signals derived from odontogenic epithelium, the induction of a translucent zone and cellular proliferation in the underlying mesenchyme may be related to the growth-promoting potential of embryonic epithelia and not be specific to signals derived from the odontogenic epithelium. Similar to mouse odontogenic epithelium, agarose beads soaked in recombinant BMP-4 induced a translucent zone, cellular proliferation, and expression of Msx-1, Msx-2, and Bmp-4 in chick mandibular mesenchyme after 24 hours. These observations together showed that avian mandibular mesenchyme has odontogenic potential that is expressed upon interactions with inductive signals from mouse odontogenic epithelium. Similar to odontogenesis in vivo, formation of dental mesenchyme in chick mandibular mesenchyme is mediated by the activation of Msx-1, Msx-2, and Bmp-4.
先前的观察表明，在牙发生的起始阶段，来自小鼠牙源性上皮的信号能够在从异位部位分离出的非牙源性但神经嵴衍生的间充质中诱导出牙，这些异位部位包括鸡的下颌间充质。在本研究中，利用E11小鼠牙源性上皮与23期鸡下颌外侧间充质之间的异种特异性重组，研究了鸡下颌间充质中异位牙胚和牙间充质的形成。形态学标准以及针对Msx-1、Msx-2和Bmp-4 mRNA的鸡特异性探针都被用作早期牙间充质的标志物。我们的结果表明，小鼠牙源性上皮与鸡下颌间充质的相互作用诱导了鸡下颌间充质的早期变化，包括出现一个透明区、细胞增殖以及Msx-1、Msx-2和Bmp-4表达的诱导，这些已被证明与牙间充质的形成有关。此外，在异种特异性重组6天后，形成了在形态和基因表达模式上都类似于体内E13牙胚的牙胚样结构。这些牙胚样结构由内陷的小鼠下颌上皮和浓缩的鸡下颌间充质组成，后者表达高水平的Msx-1和Bmp-4，但Msx-2水平检测不到。与在下方间充质中诱导Msx-1、Msx-2和Bmp-4不同，后者是牙源性上皮衍生信号所特有的，下方间充质中透明区的诱导和细胞增殖可能与胚胎上皮的生长促进潜能有关，而不是牙源性上皮衍生信号所特有的。与小鼠牙源性上皮类似，浸泡在重组BMP-4中的琼脂糖珠在24小时后诱导了鸡下颌间充质中的透明区、细胞增殖以及Msx-1、Msx-2和Bmp-4的表达。这些观察结果共同表明，禽类下颌间充质具有牙源性潜能，在与小鼠牙源性上皮的诱导信号相互作用时得以表达。与体内牙发生类似，鸡下颌间充质中牙间充质的形成是由Msx-1、Msx-2和Bmp-4的激活介导的。
