Regulation of Stem Cell

Abstract

The central dogma in gene expression is “DNA makes the RNA, a process called as transcription; and RNA makes the protein, called as translation.” Gene expression can be regulated at the stage of transcription, RNA processing (posttranscriptional changes), and translation. Organisms have been classified into two groups—Prokaryotes whose cells do not have distinct well-defined nucleus, and eukaryotes whose cells have distinct well-defined nucleus. Examples of prokaryotes are bacteria and the blue green algae and of eukaryotes are animals, plants and fungi. In prokaryotes, the RNA primary product may itself be the target of regulation. In eukaryotic cells, due to compartmentation, transport of mRNA from the nucleus to the cytoplasm could be an additional target for regulation. However, bacterial mRNA is directly available for protein biosynthesis soon after its synthesis. Regulation of transcription usually occurs at the stage of initiation. The regulators of initiation of transcription may be a protein or RNA. In prokaryotes, on–off of transcription is the main regulatory control of the gene expression, whereas, in eukaryotes, more complex regulatory mechanism of transcription takes place. In addition, RNA splicing also plays major role in the regulation of gene expression. Here, it is pertinent to mention that eukaryotic genes have been found to have coding as well as noncoding sequences. In fact, as per recent human genome sequence data, more than 50% sequences are noncoding sequences whose function is also not clear. These are called introns or junk sequences. The coding sequences are called exons. Of course, there are regulatory elements too. The primary transcript of DNA has complementary sequences of both exons and introns and is called heterogenous RNA (HnRNA). The HnRNA gets spliced removing introns and ligating exons. Regulation of gene expression in both prokaryotes and eukaryotes is important since it decides whether a particular protein should be synthesized and in which quantity. Keywords: Alternate Splicing; Attenuation; CAAT Box; Cyclic AMP Receptor Protein (CRP or CAP); Exon; Gratuitous Inducer; Intron or Intervening Sequence; Inducer; Induction; Lariat; Leader Sequence; Operator; Polyadenylation; Polycistronic mRNA; Promoter; Regulatory Gene; Repression; Ribozyme; SnRNAs (Small Nuclear RNAs); SnRNPs; Splicing; TATA box; Telomerase; Telomere; Upstream