人胚胎肝干细胞的形态特点

目的:观察胚胎发育早期肝干细胞的形态特征、时空分布及分化,以探讨肝干细胞的生物学特征．方法:运用发育第3-12 wk人胚标本47例(其中 3．5 wk各8例;6-8 wk各5例,9-12 wk各2例),石蜡切片,连续切片,免疫组化染色,光镜下观察人胚肝及肝干细胞的发育及其AFP、c-Met和 CK19的时空表达．结果:发育第3 wk,肝芽形成,第4 wk形成肝索,第5 wk出现原始肝血窦．第3-5 wk人胚肝芽和肝索细胞排列紧密,较小,形态不规则,核圆形或卵圆形,核质比例大,核深染,胞质颜色较淡,偏蓝色,显示出幼稚细胞的形态学特征,并呈甲胎蛋白(α-Fetoprotein,AFP)、c-Met 阳性反应．第6 wk,肝索内出现了体积大、核大、淡染的细胞,呈AFP、c-Met阴性反应．随胚龄增加,这类细胞数量增加．10-12 wk． AFP、c-Met阳性细胞主要分布于汇管区周围． CK19阳性反应在7 wk时开始出现于一些与 AFP、c-Met阳性反应的细胞形态类似的肝索细胞中．10-11 wk时,CK19阳性反应主要位于汇管区附近的肝索细胞、胆管板细胞及胆管上皮细胞,12 wk时,CK19阳性信号仅见于胆管板和胆管上皮细胞．此时所有的胆管板细胞及胆管上皮细胞均呈AFP、c-Met和CK19阳性．结论:人胚发育3-5 wk肝实质由肝干细胞组成,其表型为AFP /c-Met ．6 wk,肝干细胞开始向肝细胞系分化,7 wk向胆管系分化,10-12 wk,肝干细胞主要局限于汇管区周围的肝索, 与成年肝中卵圆细胞(成年肝干细胞)的分布一致．AFP ／c-Met／ CK19 细胞可能为胆管祖细胞．

Morphological characteristics of human embryonic hepatic stem cells

AIM: To observe the morphological features, temporal-spatial distribution and differentiation of hepatic stem cells in the early stage of human embryonic livers. METHODS: Paraffin sections were prepared from human embryos of 3 to 12 wk by routine method. Immunohistochemical staining was used to observe the development of human embryonic livers and hepatic stem cells as well as the expression of a-fetoprotein (AFP), c-Met and cytokeratin 19 (CK19) under light microscope. RESULTS: Liver buds came into being in wk 3, hepatic cords formed in wk 4, and primal hepatic sinusoids were found in wk 5. The hepatic cells of the 3-5 wk displayed the typical features of immature cells: small size, a round or ovoid nuclei with dark color, scant cytoplasm with slight blue and a high ratio of nuclei to cytoplasm. Moreover, they were positive for AFP and c-Met. At 6 wk, a part of hepatocytes, whose numbers increased as the growth of the embryos, became larger with nuclei of slight color, which were negative for AFP and c-Met. At 10-12 wk, the AFP- and c-Met-positive cells were mainly found at the periportal region. The CK19-positive reaction began to appear in some hepatocytes which were similar to the AFP- and c-Met-positive cells at 7 wk. At 10-11 wk, the reaction was confined at the hepatocytes adjacent to the portal region, ductal plate and biliary epithelial cells. At 12 wk, the positive reaction was only found at the ductal plate and biliary epithelial cells. Furthermore, all the cells were positive for AFP, c-Met and CK19 at this time. CONCLUSION: Hepatocytes of 3-5 wk, pheno-typed AFP /c-Met , are homogenous and belong to the hepatic stem cells. At 6 wk, the hepatic stem cells begin to differentiate to hepatocyte system, and then to cholangiocyte system in the next week. Like oval cells in the adult liver, the hepatic stem cells mainly locate at the periportal region at 10-12 wk. The cells characterized by AFP /c-Met /CK19 belong to the progenitor cells of biliary epithelial cells.