中文摘要：

目的：探讨丁酸钠、激活素A（activin A）和地塞米松诱导小鼠胚胎干细胞（ES细胞）分化为胰腺外分泌细胞的可行性，并对诱导作用进行比较。方法：小鼠ES细胞悬浮培养为拟胚体后，以不同浓度的丁酸钠（1mmol／L，2mmol／L，3mmol／L）诱导分化，通过RT—PCR检测不同时点胰腺特异性外分泌基因的表达水平，确定丁酸钠诱导ES细胞向胰腺外分泌细胞分化的最佳浓度和作用时间。进一步单独或联合应用丁酸钠、activin A、地塞米松诱导Es细胞分化，并通过细胞形态学变化、RT—PCR和免疫荧光检测观察不同诱导方案对胰腺外分泌基因和蛋白表达的影响，确定最佳诱导方案。结果：1mmol／L丁酸钠能明显促进胰腺外分泌基因amylase、ehymotrypsinogen、elastasel、elastase2和earboxypeptidase的表达，随着丁酸钠浓度的增加，丁酸钠的诱导作用逐渐减弱；1mmol／L丁酸钠诱导第3d后可检测到amylase、ehymotrypsinogen、elastasel、elastase2和earboxypeptidase的表达，在第5d外分泌基因mRNA表达水平达到高峰，随后逐渐下降。与自发对照组相比，单独应用丁酸钠、activinA、地塞米松诱导ES细胞分化，均能提高amylase、ehymotrypsinogen、elastasel、elastase2和earboxypeptidase的表达水平。但联合应用丁酸钠、aetivinA、地塞米松诱导后，ES细胞形态更为均一，上述胰腺外分泌基因的表达进一步增强；免疫荧光结果显示amylase表达为阳性。结论：低浓度的丁酸钠、activinA以及地塞米松均可以诱导小鼠ES细胞胰腺外分泌基因的表达，多种诱导因子的联合作用能明显提高胰腺外分泌细胞的诱导效率。

英文摘要：

AIM： To explore the effects of sodium butyrate, activin A and dexamthasone on inducing mouse embryonic stem （ES） cells to differentiate into exocrine pancreatic cells in vitro. METHODS： El4 mouse ES cells were cultured in suspension to form embryonic bodies （EBs）. The EBs were cultured with differentiating medium containing different concentrations of sodium butyrate, and the spontaneously differentiated ES cells were used as control. Exocrine pancreatic genes such as amylase, chymotrypsinogen, elastase 1, elastase 2 and carboxypeptidase were detected by RT - PCR at different time points to determine the optimal concentration and exposure time of sodium butyrate. Furthermore, activin A or dexamthasone was also used to explore the effects on exocrine differentiation. After that, the combination of sodium butyrate, activin A and dexamthasone was used to promote the differentiation of exocrine pancreatic cells from ES cells. During the differentiation course, the gene expressions of amylase, chymotrypsinogen, elastase 1, elastase 2 and carboxypeptidase were detected by RT - PCR. Morphological changes were investigated by phase contrast microscopy. Amylase expression was examined by immunofluorescence staining. RESULTS： Exocrine pancreatic gene expressions such as amylase, chymotrypsinogen, elastase 1, elastase 2 and carboxypeptidase were detected in spontaneously differentiated EBs. A relatively lower concentration of sodium butyrate with a shorter exposure time significantly promoted those above gene expressions as compared to that of spontaneously differentiated EBs. Activin A and dexamethasone induced upregulation of exocrine gene expression. The combination of activin A, sodium butyrate and dexamethasone significantly enhanced the mRNA levels of amylase, chymotrypsinogen, elastase 1, elastase 2 and carboxypeptidase. Under the treatment of activin A, sodium buryrate and dexamethasone, differentiated cells were polygonal in shape with large, round, and center - situated nuclei. According to the obser