http://www.100md.com
2003年10月26日
By Mehdi Banan, Ph.D.
Science Content/Business Development Analyst
Kawasaki H, Taira K. (2003) Hes1 is a target of microRNA-23 during retinoic-acid-induced neuronal differentiation of NT2 cells. Nature 423:838-42. [view]
MicroRNAs (miRNAs) are 21-23 bp RNA molecules that are processed from larger 70-90 bp stem-looped precursors. To date, over 150 miRNAs have been identified in such diverse organisms as worms, fruit flies, humans, and plants (1). The function of most miRNAs is not known. A few miRNAs, however, have been shown to play roles in developmental timing (in worms) and cell proliferation (in fruit flies) by inhibiting the expression of downstream genes (2). Two mechanisms of gene suppression by miRNAs have so far been identified. In one, miRNAs bind to partially complementary regions in the 3' untranslated region (3'UTR) of target transcripts to suppress translation. In the other, the miRNAs bind to perfectly complementary target mRNAs and degrade them via the RNAi pathway.
In the 19 June 2003 issue of Nature, Kawasaki and Taira report on a novel function for a human miRNA. The authors show that miRNA-23 is involved in the differentiation of a human neuronal cell line--a function that is carried out via translational suppression of the Hes1 gene (3). These findings are significant because a function for a human miRNA is identified for the first time.
A Link Between miRNA-23 and Hes1
In order to identify miRNA-23 target genes, Kawasaki and Taira searched the NCBI DNA database for genes with exact matches to human miRNA-23. In their search the best match was found near the termination codon of Hes1 (77% homology)--a basic helix-loop-helix transcriptional repressor that is part of the Notch signaling pathway.
To determine whether the Hes1 mRNA is actually a target for miRNA-23, the authors used NT2 cells as a model system. NT2 cells are embryonic carcinoma cells that differentiate into neuronal cells upon retinoic acid treatment. The authors hypothesized that this differentiation might be dependent on suppression of Hes1 expression by miRNA-23, since it was known that Hes1 up-regulation suppresses neuronal differentiation (4). To confirm their hypothesis, the authors first determined that the levels of HES1 protein (but not Hes1 mRNA) decrease after NT2 cells are treated with retinoic acid. More importantly, they determined that this decrease is accompanied by an increase in miRNA-23 levels. These results suggested that the increase in miRNA-23 levels was causing the reduction in HES1 protein levels in differentiating NT2 cells.
To confirm that miRNA-23 is directly responsible for suppression of HES1 expression, two approaches were taken. In one, synthetic miRNA-23 was introduced into undifferentiated NT2 cells (with their high HES1 levels and low miRNA-23 levels). This resulted in a decrease in expression levels of HES1 protein. In the other, siRNAs targeting miRNA-23 were introduced into differentiated NT2 cells (with their low HES-1 levels and high miRNA-23 levels). This led to a decrease in miRNA-23 levels and an increase in HES-1 levels.
The Role of miRNA-23 in Differentiation of NT2 Cells
The authors then showed that expression of miRNA-23 is responsible for the differentiation of NT2 cells (presumably via a reduction in HES1 protein levels). To this end, the authors made use of two protein markers--SSEA-3, which is only expressed in undifferentiated NT2 cells, and MAP2, which is only expressed in differentiated NT2 cells. Using these markers, the authors showed that addition of siRNAs targeting miRNA-23 prevents the differentiation of NT2 cells upon retinoic acid treatment. This blockage, however, is reversed by addition of synthetic miRNA-23.
Discussion
The results by Kawasaki and Taira suggest that suppression of HES1 expression by miRNA-23 is necessary for the differentiation of NT2 cells. It is interesting to note that in addition to miRNA-23, several worm and fruit fly miRNAs have been shown to play roles in development. It is therefore possible that other mammalian, worm, or fruit fly miRNAs also play roles in various developmental processes. This premise is supported by the differential spatial and temporal pattern of miRNA expression in various organisms.
To date, over 150 miRNAs have been cloned. These miRNAs have been identified based on their size and not their function. One way to uncover the function of miRNAs is to identify their mRNA target(s). This task has proved difficult because 1) many miRNAs may be only partially complementary to target transcripts and 2) lack of complete homology to target genes makes it is difficult to identify them via alignment programs. In this regard, it is interesting to note that database searches were used to identify Hesl as a miRNA-23 target. These results suggest that database searches may lead to the identification of new miRNA targets, thus paving the way for the identification of novel functions of other miRNAs.
References
Pasquinelli AE. (2002). MicroRNAs: deviants no longer. Trends in Genet. 18(4): 171-173. Ambros V (2003). MicroRNA pathways in flies and worms: growth, death, fat, stress, and timing. Cell 113:673-676. Kawasaki H and Taira K. (2003). Hes1 is a target of microRNA-23 during retinoic-acid-induced neuronal differentiation of NT2 cells. Nature 423:838-842. Ishibashi M, Moriyoshi K, Sasai Y, Shiota K, Nakanishi S, and Kageyama R (1994). Persistent expression of helix-loop-helix factor HES-1 prevents mammalian neural differentiation in the central nervous system. EMBO J. 13:1799-1805.
Related Articles
MicroRNAs (miRNAs): A New Class of Small RNA Molecules
MicroRNAs are Found in Plants
Drosophila miRNA Functions Like an Oncogene
[1]
生物谷严正声明：转载生物谷文章请注明来自生物谷
Science Content/Business Development Analyst
Kawasaki H, Taira K. (2003) Hes1 is a target of microRNA-23 during retinoic-acid-induced neuronal differentiation of NT2 cells. Nature 423:838-42. [view]
MicroRNAs (miRNAs) are 21-23 bp RNA molecules that are processed from larger 70-90 bp stem-looped precursors. To date, over 150 miRNAs have been identified in such diverse organisms as worms, fruit flies, humans, and plants (1). The function of most miRNAs is not known. A few miRNAs, however, have been shown to play roles in developmental timing (in worms) and cell proliferation (in fruit flies) by inhibiting the expression of downstream genes (2). Two mechanisms of gene suppression by miRNAs have so far been identified. In one, miRNAs bind to partially complementary regions in the 3' untranslated region (3'UTR) of target transcripts to suppress translation. In the other, the miRNAs bind to perfectly complementary target mRNAs and degrade them via the RNAi pathway.
In the 19 June 2003 issue of Nature, Kawasaki and Taira report on a novel function for a human miRNA. The authors show that miRNA-23 is involved in the differentiation of a human neuronal cell line--a function that is carried out via translational suppression of the Hes1 gene (3). These findings are significant because a function for a human miRNA is identified for the first time.
A Link Between miRNA-23 and Hes1
In order to identify miRNA-23 target genes, Kawasaki and Taira searched the NCBI DNA database for genes with exact matches to human miRNA-23. In their search the best match was found near the termination codon of Hes1 (77% homology)--a basic helix-loop-helix transcriptional repressor that is part of the Notch signaling pathway.
To determine whether the Hes1 mRNA is actually a target for miRNA-23, the authors used NT2 cells as a model system. NT2 cells are embryonic carcinoma cells that differentiate into neuronal cells upon retinoic acid treatment. The authors hypothesized that this differentiation might be dependent on suppression of Hes1 expression by miRNA-23, since it was known that Hes1 up-regulation suppresses neuronal differentiation (4). To confirm their hypothesis, the authors first determined that the levels of HES1 protein (but not Hes1 mRNA) decrease after NT2 cells are treated with retinoic acid. More importantly, they determined that this decrease is accompanied by an increase in miRNA-23 levels. These results suggested that the increase in miRNA-23 levels was causing the reduction in HES1 protein levels in differentiating NT2 cells.
To confirm that miRNA-23 is directly responsible for suppression of HES1 expression, two approaches were taken. In one, synthetic miRNA-23 was introduced into undifferentiated NT2 cells (with their high HES1 levels and low miRNA-23 levels). This resulted in a decrease in expression levels of HES1 protein. In the other, siRNAs targeting miRNA-23 were introduced into differentiated NT2 cells (with their low HES-1 levels and high miRNA-23 levels). This led to a decrease in miRNA-23 levels and an increase in HES-1 levels.
The Role of miRNA-23 in Differentiation of NT2 Cells
The authors then showed that expression of miRNA-23 is responsible for the differentiation of NT2 cells (presumably via a reduction in HES1 protein levels). To this end, the authors made use of two protein markers--SSEA-3, which is only expressed in undifferentiated NT2 cells, and MAP2, which is only expressed in differentiated NT2 cells. Using these markers, the authors showed that addition of siRNAs targeting miRNA-23 prevents the differentiation of NT2 cells upon retinoic acid treatment. This blockage, however, is reversed by addition of synthetic miRNA-23.
Discussion
The results by Kawasaki and Taira suggest that suppression of HES1 expression by miRNA-23 is necessary for the differentiation of NT2 cells. It is interesting to note that in addition to miRNA-23, several worm and fruit fly miRNAs have been shown to play roles in development. It is therefore possible that other mammalian, worm, or fruit fly miRNAs also play roles in various developmental processes. This premise is supported by the differential spatial and temporal pattern of miRNA expression in various organisms.
To date, over 150 miRNAs have been cloned. These miRNAs have been identified based on their size and not their function. One way to uncover the function of miRNAs is to identify their mRNA target(s). This task has proved difficult because 1) many miRNAs may be only partially complementary to target transcripts and 2) lack of complete homology to target genes makes it is difficult to identify them via alignment programs. In this regard, it is interesting to note that database searches were used to identify Hesl as a miRNA-23 target. These results suggest that database searches may lead to the identification of new miRNA targets, thus paving the way for the identification of novel functions of other miRNAs.
References
Pasquinelli AE. (2002). MicroRNAs: deviants no longer. Trends in Genet. 18(4): 171-173. Ambros V (2003). MicroRNA pathways in flies and worms: growth, death, fat, stress, and timing. Cell 113:673-676. Kawasaki H and Taira K. (2003). Hes1 is a target of microRNA-23 during retinoic-acid-induced neuronal differentiation of NT2 cells. Nature 423:838-842. Ishibashi M, Moriyoshi K, Sasai Y, Shiota K, Nakanishi S, and Kageyama R (1994). Persistent expression of helix-loop-helix factor HES-1 prevents mammalian neural differentiation in the central nervous system. EMBO J. 13:1799-1805.
Related Articles
MicroRNAs (miRNAs): A New Class of Small RNA Molecules
MicroRNAs are Found in Plants
Drosophila miRNA Functions Like an Oncogene
[1]
生物谷严正声明：转载生物谷文章请注明来自生物谷