Yamasaki Harufumi, Sada Aiko, Iwata Takeyuki, Niwa Tohru, Tomizawa Minoru, Xanthopoulos Kleanthis G, Koike Toru, Shiojiri Nobuyoshi
Department of Biology, Faculty of Science, Shizuoka University, 836 Oya, Surugaku, Shizuoka City, Shizuoka 422-8529, Japan.
Development. 2006 Nov;133(21):4233-43. doi: 10.1242/dev.02591. Epub 2006 Oct 4.
The expression of C/EBPalpha, which may govern transcription of mature hepatocyte marker genes, was suppressed in periportal hepatoblasts in mouse liver development, leading to biliary cell differentiation. This study was undertaken to analyze how inactivation of the Cebpa gene affects biliary cell differentiation and gene expression of the regulatory genes for that differentiation, including Hnf1b and Hnf6. In the knockout mouse liver at midgestation stages, pseudoglandular structures were abundantly induced in the parenchyma with elevated expression of Hnf6 and Hnf1b mRNAs. The wild-type liver parenchyma expressed mRNAs of these transcription factors at low levels, though periportal biliary progenitors had strong expression of them. These results suggest that expression of Hnf6 and Hnf1b is downstream of C/EBPalpha action in fetal liver development, and that the suppression of C/EBPalpha expression in periportal hepatoblasts may lead to expression of Hnf6 and Hnf1b mRNAs. Immunohistochemical studies with biliary cell markers in knockout livers demonstrated that differentiated biliary epithelial cells were confined to around the portal veins. The suppression of C/EBPalpha expression may result in upregulation of Hnf6 and Hnf1b gene expression, but be insufficient for biliary cell differentiation. When liver fragments of Cebpa-knockout fetuses, in which hepatoblasts were contained as an endodermal component, were transplanted in the testis of Scid (Prkdc) male mice, almost all hepatoblasts gave rise to biliary epithelial cells. Wild-type hepatoblasts constructed mature hepatic tissue accompanied by biliary cell differentiation. These results also demonstrate that the suppression of C/EBPalpha expression may stimulate biliary cell differentiation.
C/EBPα 的表达可能调控成熟肝细胞标记基因的转录，在小鼠肝脏发育过程中，其在汇管区周围的肝母细胞中受到抑制，从而导致胆管细胞分化。本研究旨在分析Cebpa基因失活如何影响胆管细胞分化以及该分化调控基因的基因表达，这些调控基因包括Hnf1b和Hnf6。在妊娠中期的基因敲除小鼠肝脏中，实质内大量诱导出假腺泡结构，同时Hnf6和Hnf1b mRNA的表达升高。野生型肝脏实质中这些转录因子的mRNA表达水平较低，尽管汇管区胆管祖细胞有较强的表达。这些结果表明，在胎儿肝脏发育中，Hnf6和Hnf1b的表达处于C/EBPα 作用的下游，并且汇管区肝母细胞中C/EBPα 表达的抑制可能导致Hnf6和Hnf1b mRNA的表达。对基因敲除肝脏中胆管细胞标记物的免疫组织化学研究表明，分化的胆管上皮细胞局限于门静脉周围。C/EBPα 表达的抑制可能导致Hnf6和Hnf1b基因表达上调，但不足以实现胆管细胞分化。当含有肝母细胞作为内胚层成分的Cebpa基因敲除胎儿的肝脏片段移植到Scid（Prkdc）雄性小鼠的睾丸中时，几乎所有肝母细胞都分化为胆管上皮细胞。野生型肝母细胞构建了伴有胆管细胞分化的成熟肝组织。这些结果还表明，C/EBPα 表达的抑制可能刺激胆管细胞分化。
