Welcome to the microRNA world!
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About miRNAs
MicroRNAs (miRNAs) are 20-22
nucleotide small, RNA molecules encoded in the genomes of plants and animals
that are known to regulate the expression of genes by binding (generally) to
the 3'-untranslated regions (3'-UTR) of target mRNAs.
The human genome has been known to contain a lot (~97%) of “junk”
or non-coding DNA (Mattick 2005; Mattick and Makunin 2006). Although the level of complexity is much
higher in humans as compared to simpler life forms (such as plants), the number
of protein coding genes in humans is far less than that seen in some plants
(~25,000 in humans Vs 40,000 in rice).
Increasing number of studies in the recent years provide significant
insights to understanding the role of non-coding(nc)RNAs in cellular development
and function. We and others have
demonstrated that microRNAs(miRNAs), a class of ncRNAs, are essential for
normal development and function of endocrine pancreas (Poy et al. 2004;
Joglekar et al. 2007a; Kloosterman et al. 2007; Lynn et al. 2007; Avnit-Sagi et
al. 2009; Baroukh and Van Obberghen 2009; Correa-Medina et al. 2009; Joglekar
et al. 2009a; Morita et al. 2009; Poy et al. 2009).
Although the first published
description of miRNAs appeared in 1993 (Lee et al 1993), it has only been in the last 6-7
years that the breadth and diversity of this class of small, regulatory RNAs
been appreciated. A great deal of effort has gone into understanding how, when,
and where miRNAs are produced and function in cells, tissues, and organisms.
Each microRNA may regulate multiple genes (often dozens) and since hundreds of
miRNA genes are predicted to be present in higher eukaryotes (Lim 2003) the
potential regulatory circuitry afforded by microRNA is enormous. Several
research groups have provided evidence that miRNAs may act as key regulators of
processes as diverse as early development (Reinhart 2000), cell proliferation
and cell death (Brennecke 2003), apoptosis and fat metabolism (Xu 2003), and
cell differentiation (Dostie 2003, Chen 2003). Recent studies of miRNA
expression implicate miRNAs in brain development (Krichevsky 2003), chronic
lymphocytic leukemia (Calin 2004), colonic adenocarcinoma (Michael 2003),
Burkitt’s Lymphoma (Metzler 2004), and viral infection (Pfeffer 2004)
suggesting possible links between miRNAs and viral disease, neurodevelopment,
and cancer. There is speculation that in higher eukaryotes, the role of miRNAs
in regulating gene expression could be as important as that of transcription
factors.
In the past 4 years, we have
focused on understanding the role of specific transcription factors and miRNAs
in endocrine pancreas development and function (Joglekar et al. 2007a; Joglekar
et al. 2007b; Joglekar et al. 2009a; Joglekar et al. 2009b). Initial studies were carried out using
TaqMan-based low density arrays (TLDAs), to understand the expression of known
and validated microRNAs that are expressed during embryonic development of
human pancreas. In the past year,
we have focused our studies using next generation sequencing (SOLiD system,
Applied Biosystems/ Life Technologies) to assess different microRNAs (and other
ncRNAs) that are expressed during human pancreas development. Although, the role of specific
microRNAs, such as miR-375, in islet development and function has become more
evident (Poy et al. 2004; Keller et al. 2007; Avnit-Sagi et al. 2009; Baroukh
and Van Obberghen 2009; Joglekar et al. 2009a; Poy et al. 2009), we do not have
information on the expression of miR-375 and other islet-specific microRNAs in
diabetic humans.
The interest of the Hardikar
Laboratory in miRNAs has been since beginning of 2006. We are interested in looking at the role
of different miRNAs in post-transcriptional gene regulation during pancreas
development and regeneration.
Studies carried out in our lab and several other laboratories worldwide
demonstrate that miRNAs are involved in determination of cell fate during
pancreas development. Using Taqman
based assays from Applied Biosystems (AB), we have assessed miRNA profiles from
several tissues during mouse embryonic development. Identification of specific miRNAs during
pancreatic islet development would help us in understanding the miRNAs that may
be involved in differentiation of endocrine pancreatic progenitor cells. We use miRNA real time pcr assays
(human, mouse and rat) from Applied Biosystems,