Categories
Biology

Summary of 3 articles

Biology

Introduction

RNA interference (RNAi) is a mechanism by which RNA molecules inhibit gene expression sometimes by destroying mRNA molecules. Co-suppression, post transcriptional gene silencing (PTGS), and quelling are some other names by which the process has been described before it was discovered.  Andrew Fire and Craig C. Mello in 2006 shared the Nobel Prize in Physiology or Medicine due to their significant contributions to the discovery of RNAi. These significant contributions were published in 1998 (Bagasra & Prilliman, 2004).

The topic of this paper is to debate is whether the 2006 Nobel Prize Award Committee fair  or correct in their selection when Andy Fire and Craig Mello were awarded the Big Prize instead of giving a share of it to one other or a group of scientists?

Analysis

Studies conducted by Carolyn Napoli, Christine Lemieux, and Richard Jorgensen (1990) prior to Mello and Fires (1998) were aimed at verifying that the  introduction of a Chimeric Chalcone Synthase Gene into Petunia Results in Reversible Co-Suppression of

Homologous Genes Ín trans. At first they ‘attempted to overexpress chalcone synthase (CHS) in pigmented petunia petals by introducing a chimeric petunia CHS gene’ (Napoli, Lemieux & Jorgensen, 1990).  The scientists employed plasmid constructions; plant transformation and the use of RNase Protections in investigating the phenomenon (Napoli et.al, 1990).

Precisely, attempts at overexpressing chalcone synthase (CHS) in pigmented petunia petals were made. Surprisingly, this gene caused a block in anthocyanin biosynthesis. Results showed where in 42% of plants, which had the gene CHS introduced, totally white flowers emerged. Besides, patterned flowers with white or pale nonclonal sectors on a wild-type pigmented background appeared. Further, it was discovered that the control plants show any of the phenotypes seen on the ones in which the chimeric petunia CHS gene was introduced (Napoli et.al, 1990).

When progeny testing of one plant was undertaken the novel color phenotype co-segregated

after CHS gene was introduced. A phenotypically wild type was observed when progeny was conducted in the absence of CHS gene. Subsequently, a variable was discovered in the somatic and germinal stability of the novel color patterns.  With further analysis of various portions of the experiment scientist concluded that, ‘in the altered white flowers, the expression of both genes was coordinately suppressed’ (Napoli et.al, 1990).

It meant that the introduction of CHS gene alone was not enough to create a suppression of endogenous CHS transcript levels because the experiment clearly showed that it needed the expression of both genes. Therefore, the mechanism supporting the reversible co-suppression of homologous genes in trans is still obscure. The involvement of methylation may be possible because these researchers introduced a gene which created a block in anthocyanin biosynthesis. As such, it can be deducted that these scientists were inconclusive regarding the extent to which reversible co-Suppression of homologous genes Ín trans is made since the actual mechanism could not be identified (Napoli et.al, 1990).

To this extent Fire and Mello (1998) discovery became very significant to the science. Along with other scientist they set out to find out the sequence of the missing combination in the mechanism and whether it could be identified in human/animal species, ‘here we

investigate the requirements for structure and delivery of the interfering RNA. To our surprise, we found that double-stranded RNA was substantially more effective at producing interference

than was either strand individually’(Fire et.al, 1998).

They together realized that even though the usefulness of RNA interference in C. elegans was identified; two aspects of the process created some measure of concern in its explanation. They cited ‘sense and antisense RNA preparations are each sufficient to cause interference3, 4…… interference effects can persist well into the next generation, even though many endogenous RNA transcripts are rapidly degraded in the early are rapidly degraded in the early embryo5’ (Fire, Xu, Montgomery, Kostas, Driver & Mello, 1998).

Like Napoli (1990) and others they realized that the mechanism supporting the reversible co-suppression of homologous genes in trans is still obscure (Napoli et.al, 1990). However, these researchers injected adult animals with single purified strands. These had the most a modest effect; double-stranded mixtures caused potent and specific interference (Fire et.al, 1998).

Consequently, these scientists used this phenomenon to test the possibility that the contrast

between native RNAs behavior (such as mRNA) and the molecules responsible for the inference reflects an underlying difference in RNA structure. Unlike Napoli (1990) whereby they introduced a Chimeric Chalcone Synthase Gene these scientists injected RNA into cells in certain biological systems to interfere with the function of an endogenous gene1,2 (Fire et .al, 1998).

The researchers further advanced that the difference could be due to a simple antisense mechanism influenced by hybridization between the injected RNA and endogenous messenger RNA transcripts.  In their experiments they used RNA interference in the nematode Caenorhabditis elegans for manipulation of gene expression3,4. Through this process they were able to evaluate the structural requirements and delivery for interfering RNA (Fire et. al, 1998).

There have been significant differences between Fire and Mello’s work and other scientists. For example, Andrew J. Hamilton and David C. Baulcombe (1999) discovered ‘A Species of Small Antisense RNA in Posttranscriptional Gene Silencing in Plants.’

This is a nucleotide sequence-specific defense mechanism which targets cellular and viral mRNA. Three types of transgene-induced PTGS were identified in the sequence. One example of virus induced PTGS was evaluated in the plants sampled (Hamilton & Baulcombe, 1999)

The antisense RNA complementary related to targeted mRNA was identified in each case. They were 25 nucleotides and at a uniform length.  Precisely, their accumulation was accessed either from transgene sense transcription or RNA virus replication.  As such, the conclusion drawn was that the 25-nucleotide antisense RNA would appear to have been ‘synthesized from an RNA template and may represent the specificity determinant of PTGS (Hamilton & Baulcombe, 1999).

Prior to publishing these results Fires (1998) and counterparts had discovered a sequence relating the RNAi which could have been detected by Napoli (1990) and his colleagues. Hamilton and Baulcombe (1999) further explored the sequencing in plants to conclude that the 25-nucleotide antisense RNA would appear to have been ‘synthesized from an RNA template and may represent the specificity determinant of PTGS (Hamilton & Baulcombe, 1999). The advantage of Fire’s (1998) and counterparts research project and discovery was that they extend the phenomenon beyond plants to include animals and humans.

Conclusion

Pros and Cons of Nobel Prize Award

Recipients of the 2006 Nobel Prize Awards, Fire and Mello (1998) were not the only scientists conducting research in RNA studies. Many other scientists were involved and came close to discovering the mechanism by which Co-suppression, post transcriptional gene silencing (PTGS), and quelling emerged. Precisely, these were the concepts used in researching the phenomenon prior to Fire and Mello’s (1998) report.

Besides, the 1998 Nature report was compiled by Andrew Fire, SiQun Xu, Mary K. Montgomery Steven A. Kostas Samuel E. Driver and Craig C. Mello (1998). Therefore, was the 2006 Nobel Prize Award Committee fair in their selection when Andy Fire and Craig Mello were awarded the Big Prize instead of giving a share of it to one other or a group of scientists?

One wonders whether there was an oversight by the committee when only Fires and Mello (1998) were selected for this prize after so many other scientists were involved in the exploring and discovering elements of gene inhibition expression by RNA activity. Questions pertaining to whether the other scientists involved were contracted as nominees or were they overlooked by the prize selecting institution after nomination ought to be explored. Clearly, the group which presented this Nature report ought to have received this award.

Works cited

Bagasra O, Prilliman KR.  RNA interference: the molecular immune system. J. Mol. Histol. Vol 35, 6: 545–53. 2004. Print

Editorial. Access: A Nobel prize: Nature Chemistry. Nature Chemistry Vol 1, 7: 509. 2009. Print

Fire, Andrew;  Xu, SiQun; Montgomery, Mary;  Kostas, Stephen; Driver, Samuel; Mello, Craig. Potent and specific genetic interference by double-stranded RNA in Caenorhabditis elegans. Nature. Vol 391, 19: 896 – 910. 1998. Print.

Hamilton, Andrew; Baulcombe, David. A Species of Small Antisense RNA in Posttranscriptional Gene Silencing in Plants. Science. Vol 286: 950-1000. 1999. Print

Napoli, Carolyn; Lemieux, Christine; Jorgensen, Richard. lntroduction of a Chimeric Chalcone Synthase Gene into Petunia Results in Reversible Co-Suppression of Homologous Genes Ín Trans. The Plant Cell, Vol. 2, 279-289.1990. Print