Iowa Institute for Oral Health Research, University of Iowa College of Dentistry and Dental Clinics, Iowa City, Iowa, United States of America.
Department of Anatomy and Cell Biology, University of Iowa Carver College of Medicine, Iowa City, Iowa, United States of America.
PLoS Genet. 2024 Jul 25;20(7):e1011364. doi: 10.1371/journal.pgen.1011364. eCollection 2024 Jul.
How the dorsal-ventral axis of the vertebrate jaw, particularly the position of tooth initiation site, is established remains a critical and unresolved question. Tooth development starts with the formation of the dental lamina, a localized thickened strip within the maxillary and mandibular epithelium. To identify transcriptional regulatory networks (TRN) controlling the specification of dental lamina from the naïve mandibular epithelium, we utilized Laser Microdissection coupled low-input RNA-seq (LMD-RNA-seq) to profile gene expression of different domains of the mandibular epithelium along the dorsal-ventral axis. We comprehensively identified transcription factors (TFs) and signaling pathways that are differentially expressed along mandibular epithelial domains (including the dental lamina). Specifically, we found that the TFs Sox2 and Tfap2 (Tfap2a/Tfap2b) formed complimentary expression domains along the dorsal-ventral axis of the mandibular epithelium. Interestingly, both classic and novel dental lamina specific TFs-such as Pitx2, Ascl5 and Zfp536-were found to localize near the Sox2:Tfap2a/Tfap2b interface. To explore the functional significance of these domain specific TFs, we next examined loss-of-function mouse models of these domain specific TFs, including the dental lamina specific TF, Pitx2, and the ventral surface ectoderm specific TFs Tfap2a and Tfap2b. We found that disruption of domain specific TFs leads to an upregulation and expansion of the alternative domain's TRN. The importance of this cross-repression is evident by the ectopic expansion of Pitx2 and Sox2 positive dental lamina structure in Tfap2a/Tfap2b ectodermal double knockouts and the emergence of an ectopic tooth in the ventral surface ectoderm. Finally, we uncovered an unappreciated interface of mesenchymal SHH and WNT signaling pathways, at the site of tooth initiation, that were established by the epithelial domain specific TFs including Pitx2 and Tfap2a/Tfap2b. These results uncover a previously unknown molecular mechanism involving cross-repression of domain specific TFs including Pitx2 and Tfap2a/Tfap2b in patterning the dorsal-ventral axis of the mouse mandible, specifically the regulation of tooth initiation site.
脊椎动物颌骨的背腹轴，特别是牙齿起始位置，是如何建立的，仍然是一个关键且未解决的问题。牙齿发育始于牙板的形成，牙板是上颌和下颌上皮内局部增厚的条带。为了鉴定控制牙板从原始下颌上皮特化的转录调控网络（TRN），我们利用激光微切割结合低输入 RNA-seq（LMD-RNA-seq）技术，对沿背腹轴的下颌上皮不同区域的基因表达进行了分析。我们全面鉴定了沿下颌上皮区域（包括牙板）差异表达的转录因子（TFs）和信号通路。具体来说，我们发现 TF Sox2 和 Tfap2（Tfap2a/Tfap2b）在沿下颌上皮的背腹轴上形成互补表达域。有趣的是，经典和新型牙板特异性 TF，如 Pitx2、Ascl5 和 Zfp536，被发现定位于 Sox2:Tfap2a/Tfap2b 界面附近。为了探索这些区域特异性 TF 的功能意义，我们接下来检查了这些区域特异性 TF 的功能丧失小鼠模型，包括牙板特异性 TF Pitx2 和腹侧外胚层特异性 TF Tfap2a 和 Tfap2b。我们发现，区域特异性 TF 的破坏导致替代区域的 TRN 上调和扩展。这种交叉抑制的重要性体现在 Tfap2a/Tfap2b 外胚层双敲除中，Pitx2 和 Sox2 阳性牙板结构的异位扩展以及腹侧外胚层中出现异位牙。最后，我们揭示了在牙齿起始部位存在一个以前未被认识的间充质 SHH 和 WNT 信号通路的界面，该界面由包括 Pitx2 和 Tfap2a/Tfap2b 在内的上皮区域特异性 TF 建立。这些结果揭示了一个以前未知的分子机制，涉及包括 Pitx2 和 Tfap2a/Tfap2b 在内的区域特异性 TF 的交叉抑制，在调节小鼠下颌的背腹轴，特别是牙齿起始位置的模式中发挥作用。
