MicroRNAs from the Planarian Schmidtea mediterranea: a model system for stem cell biology

Abstract

MicroRNAs (miRNAs) are approximately 22-nt RNA molecules that typically bind to the 3' untranslated regions of target mRNAs and function to either induce mRNA degradation or repress translation. miRNAs have been shown to play important roles in the function of stem cells and cell lineage decisions in a variety of organisms, including humans. Planarians are bilaterally symmetric metazoans that have the unique ability to completely regenerate lost tissues or organs. This regenerative capacity is facilitated by a population of stem cells known as neoblasts. Planarians are therefore an excellent model system for studying many aspects of stem cell biology. Here we report the cloning and initial characterization of 71 miRNAs from the planarian Schmidtea mediterranea. While several of the S. mediterranea miRNAs are members of miRNA families identified in other species, we also identified a number of planarian-specific miRNAs. This work lays the foundation for functional studies aimed at addressing the role of these miRNAs in regeneration, cell lineage decisions, and basic stem cell biology.

FIGURE 1.

MicroRNA families. Alignments of S. mediterranea miRNAs with family members from human, Drosophila, or C. elegans miRNAs were performed with ClustalW. In some instances, only one representative from each family is shown.

FIGURE 2.

Relationships between metazoan miRNAs. A Venn diagram depicting the number of S. mediterranea miRNAs that have family members in vertebrates, insects, or nematodes.

FIGURE 3.

Northern blot analysis of miRNA expression. Fifty micrograms of total RNA isolated from both sexual and asexual strains of S. mediterranea and another planarian, Dugesia tigrina, were resolved on 15% denaturing polyacrylamide gels and transferred to membranes. Ethidium bromide staining of the gels indicated that equal amounts of RNA were loaded into each well. The blots were probed with ³²P, 5′-end-labeled oligonucleotides complementary to the miRNAs indicated.

FIGURE 4.

A S. mediterranea miRNA cluster. The predicted secondary structure of a pre-miRNA containing miR-71b, miR-71b*, miR-2d, miR-752, and a predicted miRNA, miR-13. The sequence of the mature miRNAs is shown in red and the miRNA* strands that were identified are shown in blue.