Dictyostelium discoideum is a social amoeba that serves as a model system for RNA
interference and related mechanisms. Its position between plants and animals enables evolutionary snapshot of mechanisms and protein machinery involved in investigated subjects. MiRNAs are small regulatory RNAs that are evolutionary conserved and present in animals, plants, viruses and some prokaryotes. They have roles in development, cell growth and differentiation, apoptosis and their miss-regulation is associated with many diseases such as cancer, neurodegenerative disorders and diabetes. Recently, through sequencing of DNA libraries miRNAs have been discovered in D. discoideum.
In this work, it has been shown that heterologues miRNA let-7 can be expressed and
processed in D. discoideum. Expression of let-7 miRNA in social amoeba resulted in
a strong developmental phenotype suggesting an overload of the processing/silencing
system or/and endogenous targets. The various effects on prel-7 strain have been
observed and characterized, serving as a background for postulation of miRNA roles.
An artificial miRNA system has been established and imposed to D. discoideum,
showing that miRNAs in Dictyostelium could mediate gene expression on the level of
mRNA stability and on the posttranscriptional level. Furthermore, presence of
translational inhibition as a type of gene control was shown for the first time in this organism. Due to it new structures representing co-localities of miRNA and target mRNA have been detected.
Taken together, this work shows functional artificial miRNA system and postulates
roles of endogenous small RNA in social amoeba.