Kawasaki Tatsuki, Takahashi Masanori, Yajima Hiroshi, Mori Yoshiyuki, Kawakami Kiyoshi
Department of Oral and Maxillofacial Surgery, Jichi Medical University, 3311-1, Yakushiji, Shimotsuke, Tochigi, 329-0498, Japan.
Division of Biology, Center for Molecular Medicine, Jichi Medical University, 3311-1, Yakushiji, Shimotsuke, Tochigi, 329-0498, Japan.
Dev Growth Differ. 2016 Aug;58(6):530-45. doi: 10.1111/dgd.12291. Epub 2016 May 31.
The periodontal ligament (PDL) is a connective tissue that attaches the tooth cementum to the alveolar bone and is derived from dental follicle cells (DFCs). The DFCs form fibroblasts, osteoblasts, cementoblasts, and PDL stem cells (PDLSCs). We previously reported homeobox transcription factor Six1 expression in mouse DFCs. However, the role of Six1 in periodontal tissue development is largely unknown. In this study, we analyzed SIX1 expression in mouse periodontal tissue cells during postnatal development and adulthood. We also addressed the role of SIX1 in mouse periodontium development and in human cultured PDL-derived cells (PDLCs). In mouse development, SIX1 production was abundant in DFCs and PDL cells by 2 weeks, but it was greatly diminished in the PDL at 4 weeks and in adults. Although the SIX1-positive cell distribution was sparse in the adult PDL, SIX1-positive cells were observed with low expression levels. We used 5-ethynyl-2'-deoxyuridine (EdU) for cell labeling to reveal numerous EdU/SIX1-double positive cells at 2 weeks; however, a few EdU-positive cells remained at 4 weeks. The proportion of DFCs that incorporated EdU was significantly lower in Six1-deficient mice compared with wild-type mice at E18.5. In human PDLCs, SIX1 was intensely expressed, and SIX1-knockdown using siRNA reduced proliferating PDLCs. Our results suggest that SIX1 is a key proliferation regulator in mouse DFCs and human PDLCs, which provides novel insight into Six family gene function in mammals.
牙周韧带（PDL）是一种结缔组织，它将牙骨质附着于牙槽骨，起源于牙囊细胞（DFC）。DFC可形成成纤维细胞、成骨细胞、成牙骨质细胞和牙周韧带干细胞（PDLSC）。我们之前报道过同源盒转录因子Six1在小鼠DFC中的表达。然而，Six1在牙周组织发育中的作用在很大程度上尚不清楚。在本研究中，我们分析了出生后发育阶段及成年期小鼠牙周组织细胞中SIX1的表达情况。我们还探讨了SIX1在小鼠牙周发育及人培养的牙周韧带来源细胞（PDLC）中的作用。在小鼠发育过程中，到2周龄时，DFC和PDL细胞中SIX1的产生很丰富，但在4周龄时及成年小鼠的PDL中其表达大幅减少。尽管成年PDL中SIX1阳性细胞分布稀疏，但仍可观察到低表达水平的SIX1阳性细胞。我们使用5-乙炔基-2'-脱氧尿苷（EdU）进行细胞标记，发现在2周龄时有大量EdU/SIX1双阳性细胞；然而，在4周龄时仍有少数EdU阳性细胞。在E18.5时，Six1基因缺陷小鼠中掺入EdU的DFC比例明显低于野生型小鼠。在人PDLC中，SIX1表达强烈，使用小干扰RNA（siRNA）敲低SIX1可减少增殖的PDLC。我们的结果表明，SIX1是小鼠DFC和人PDLC中的关键增殖调节因子，这为哺乳动物Six家族基因功能提供了新的见解。
