Regulation of gene expression

Life of individual cells Cell cyclePathogens during infection (Shigella, EIEC)Environmental conditions (nutrients, toxic comp.)Multicellular organismsCell differentiation (individual development)Environmental conditions (nutrients, hormones)Genetic diseases, cancer

Gene expression must be regulated in time

Gene expression must be regulated in space

Gene expression must be quantitatively regulated

What happens when gene regulation goes awry?

• Developmental abnormalities (birth defects)

Down Syndrome

Regulation of gene expression

DNA methylation, epigenetic changes Transcriptional regulationMicroRNAs (miRNAs), stability of mRNA, RNA processingTranslational controlPost-translational control

Epigenetic regulation

The leading cause of RTT is sporadic mutations in a gene called MECP2, located on the X chromosome. Studies have shown that more then 95% of mutations originate from a mutated sperm.

The MECP2 gene makes a protein, also called MeCP2, believed to play a pivotal role in silencing other genes. Scientists suspect that the inability to shut down specific genes causes the

cascade of symptoms seen in RTT.

 

Rett syndromerare progressive neurological disorder that causes mental retardation, compulsive hand movements, reduced muscle tone, difficulties in walking, autism, decreased body weight, failure of the head to grow with age, and the increased presence of ammonia in the blood (hyperammonemia). Rett syndrome causes progressive disabilities in intellectual and motor development.

Methyl cytosine

binding protein 2

Regulation of trp transcription

Low tryptophane level – transcription of trp genes

High glucose – low cAMPLow lactose

Low glucose – high cAMPLow lactose

Low glucose – high cAMPHigh lactose

High glucose – low cAMPHigh lactose

Synthesis of LacZYA proteins:1. Glucose level - low glucose – high cAMP2. Lactose level - high lactose

+

-

-

-

transcription

Regulation of lac transcription

High glucose – low cAMPLow lactose

-galactosidase permease transacetylase

Low glucose – high cAMPLow lactose

Low glucose – high cAMPHigh lactose

High glucose – low cAMPHigh lactose

CAMP receptor protein

Regulation of lac transcription

Regulation of lac transcription

Lac repressor

CRP protein

Regulation by attenuation

Regulation of lac transcription

DNA microarrays – regulatory gene identifications

Differences in Genetic Organization of Prokaryotes and Eukaryotes

Monocistronic vs. polycistronic mRNADNA binding proteins (histons & other)Repetitive sequencesMore than 95% DNA is untranslatedRearrangement of some genes (amplification, Ab, T-cells, methylation)

Exons and intronsSeparated nucleus (transport of mRNA)

Regulation of eukaryotic transcription

Regulation of eukaryotic transcription

Regulation of eukaryotic transcription

MicroRNAs (miRNAs) are small, RNA molecules encoded in the genomes of plants and animals (Figure 1). These highly conserved, ~21-mer RNAs regulate the expression of genes by binding to the 3'-untranslated regions (3'-UTR) of specific mRNAs.

Although the first published description of an miRNA appeared ten years ago (Lee 1993), only in the last two to three years has 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 miRNA is thought to regulate multiple genes, and since hundreds of miRNA genes are predicted to be present in higher eukaryotes (Lim 2003b) the potential regulatory circuitry afforded by miRNA 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 2002), 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.

Figure 1. Transcription of miRNAs. Approximately 60% of miRNAs are expressed independently, 15% of miRNAs are expressed in clusters, and 25% are in introns.

miRNA Processing and Activity

Mode of Action of miRNAs in Plants and Animals