MicroRNA expression in chicken embryos.

MicroRNA (miRNA) are small single-stranded noncoding RNA that posttranscriptionally regulate gene expression. A major role of miRNA is the regulation of gene expression in developmental processes. In this study, we constructed a small RNA library from 11-d-old chick embryos and used this library to examine the miRNA expression profile of the embryos. This small RNA library was sequenced by using 454 Life Sciences pyrosequencing technology. A total of 10,466 sequences were obtained and annotated as either known chicken miRNA, miRNA that shared homology with other species, or novel miRNA. We identified the expression of 110 known chicken miRNA, 36 homologous chicken miRNA (previously unannotated in the chicken but conserved with miRNA from other species), and 14 novel chicken-specific miRNA not identified in any other species. We also demonstrated that some of the identified chicken embryonic miRNA are differentially expressed among the developing spleen, liver, or bursa. The current study demonstrates that a very diverse and dynamic set of miRNA is expressed in the embryonic chick at 11 d of incubation. The identification of miRNA present in the embryonic chicken will further aid in understanding the complexity of gene regulation during vertebrate development.