Quantitative analysis of miRNA expression in several developmental stages of human livers. 
miRNAs have been found to regulate gene expression at a posttranscriptional level in cells.  Studies have shown that expression of miRNAs is tissue-specific and developmental stage-specific.  The mechanism behind this could be explained by miRNA pathways.  We introduce the identification of miRNAs from two human fetal liver cDNA libraries by a cloning protocol.  The miRNAs detected were then analyzed in a chorionic villus tissue and four liver tissues using real-time polymerase chain reaction.  After sequencing and database searching, a total of 42 miRNAs in two fetal livers were detected.  Quantitative analysis showed that they have higher general expression in the livers of the fetal period than the adult period, and furthermore the expression levels of the miRNAs during the fetal period were dynamically changed.  Our results indicate that a special group of miRNAs may play an important role in human fetal liver development, while their roles in the adult livers are limited.