Hatboro-Horsham High School, PA
Teacher: Maria Simon
The development of an organism is an intricate process dependent upon genetic instruction. Genes exert influence through their transcription into messenger RNA
molecules (mRNAs), which are then translated into proteins. Although every cell in an organism contains the same DNA, it is obvious that cells exhibit different properties.
Neurons, for example, differ both morphologically and physiologically from epithelial cells. Furthermore, cells may produce different proteins at different times according to
various stimuli. Modulating the differential expression of genes is gene regulation, a broad mechanism encompassing processes such as RNA interference (RNAi). By determining
whether certain mRNA transcripts are ultimately translated into proteins or not, RNAi plays a critical role in biological processes such as development.
Central to the process of RNA interference are two classes of small RNA molecules known as microRNAs (miRNAs) and small interfering RNAs (siRNAs). By binding to mRNA transcripts
produced through transcription, miRNAs and siRNAs are capable of preventing mRNA translation into proteins. Both categories of small RNAs are formed when the cytoplasmic enzyme
Dicer cleaves double-stranded RNA into short fragments of nucleotides about 20 base pairs in length. One of the two strands of RNA is degraded, but the other is incorporated into
an RNA-induced silencing complex (RISC)
Mammalian development has also been observed to be affected by RNA interference, but elucidating its role has proven to be more difficult (Rao & Sockanathan, 2005). Bernstein et
al. concluded that RNAi was fundamental in vertebrate development by examining mice with defective Dicer1 genes, and consequently, also mutant Dicer enzyme products.