Transcriptional Characterization of Glioma Neural Stem Cells Diva ...

4.1 MicroRNA regulation Introduction
Figure 4.1: Classes of non-coding RNAs (ncRNAs) discovered to date: siRNA,
small interfering RNA; microRNAs, microRNAs; rasiRNAs, repeat-associated small
interfering RNAs; piRNAs, piwi-associated RNAs; endosiRNAs, endogenous small
interfering RNAs; scnRNAs, scanRNAs; tasiRNAs, trans-acting RNAs.
RNAs (rasiRNAs) in D. melanogaster [24] and, only recently, piwi-associated
RNAs (piRNAs) [23,164,523] and endogenous small interfering RNAs (en-
dosiRNAs) in mouse [485,524]. Other classes are found in ciliates, such as
scanRNAs (scnRNAs) that ensure the fidelity of genome inheritance to the
next generation [336], and plants, such as trans-acting RNAs (tasiRNAs) [509].
Today siRNAs are known to act as gene silencers if exogenously introduced in
mammals and microRNAs are well-established gene regulators in plants and
animals, including the unicellular ciliate C. reinhardtii. Also, piRNAs are un-
derstood to play a role in zebrafish - widening the regulatory horizons of such
molecules - and rasiRNAs, now considered a subset of the piRNA class, have
also been found in zebrafish [199]. In this thesis the focus will be maintained
on the role of microRNA regulation in mammals.
4.1 MicroRNA regulation
The role of microRNAs has been studied in many different tissues and path-
ways, as well as through various time points in the development of organisms.
The first microRNA, lin-4, was identified in 1993 in a genetic screen for mutants
that disrupted the timing of post-embryonic development in C. elegans [129],
and today several hundred microRNAs are known to exist in the mammalian
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