RNA Genes and Ribosomopathies

20,000

____ genes are protein coding = 2% of the genome

RNA genes

_____ —> functional noncoding RNA molecule - noncoding RNA is the end product (ex. tRNAs, rRNAs, microRNAs, long ncRNAs)

microRNA

• first identified in 1993

• 22 nucleotides in length

• participate in gene regulation by RNA interface

• cause gene silencing by binding to mRNA and degrading it

anti-miR155

hematological cancer treatment

• over-expression of miR-155 silences tumor suppressor and regulatory genes, letting malignant cells thrive

• ______ is the treatment

miR34

liver cancer treatment

• miR34 acts as a tumor suppressor and is under-expressed in liver cancer

• ____ is the treatment

Dicer

pri-miRNA —> pre-miRNA —> mature miRNA-

• pre-miRNA —> mature miRNA by which enzyme?

long ncRNAs

• >200 nucleotides long

functions:

• regulation of allelic expression (X chromosome inactivation, imprinting)

• development (lineage commitment, myogenesis)

• disease states (cancer, muscular dystrophy, heart failure)

human genome project

reference DNA sequence of most of the human nuclear genome

• 13 years, 7 countries, $2-3 billion spent

not all regions of DNA were sequenced:

• high priority: DNA euchromatin (transcriptionally accessible)

• low priority: DNA heterochromatin (transcriptionally inaccessible)

ENCODE project

primary goal: determine the role of the remaining component of the genome (non-coding DNA)

repetitive DNA sequences

functional multi-copy genes

repetitive sequences with uncertain function

actin, tubulin

functional multi-copy genes

minisatellites and microsatellites

12-100 nctd and 6-12 nctd, respectively

repetitive DNA sequences with uncertain function

triplet repeat expansion

tandem repeats cause a lot of diseases

• huntington’s, fragile X syndrome, myotonic dystrophy, Friedrich ataxia

• follows anticipation: next gen manifests with disease sooner and more servere

transposons

mobile DNA elements that are able to migrate from one location to another

• mobile/jumping genes, 0.05%, only very few can cause disease

• piece gets cut and joins somewhere else

retrotransposones

• DNA --> RNA --> reverse transcription --> DNA copy --> insertion at new location  

• More known to cause disease than transposons ex. Hemophilia  

haploinsufficiency

• that one functional copy isn’t enough to produce a normal amount of protein  

• Partial storage of one ribosomal protein can bottleneck production of ribosomal subunits  

• ex. 5 ribosome protein A + 5 ribosome protein B makes 1 ribosome  

• If there’s a reduction in protein, 3 ribosome protein A combines with 3 ribosome protein B to make ribosome  

• 2 “orphan” ribosome protein B distract the MDM2, which is normally inhibiting p53, so p53 becomes active

ribosomopathies

diseases in which ribosomes are not made properly

common features of ribosomopathies

1) bone marrow failure: Bone marrow is the most active organ in your body, constantly producing protein  

2) Skeletal defects  

3) increased chance of getting cancer (typically blood cancer)

• RBCs commonly affected - diamond blackfan and 5q-syndrome

ribosomopathies possible mechanisms

1) ribosomal haploinsufficiency —> disrupted ribosome biogenesis —> accumulation of free ribosomal proteins —> binds to MDM2 (p53 repressor) —> activated p53 —> apoptosis and cell cycle arrest —> anemia

2) relative excess of free heme: erythroid specific apoptosis, anemia

miRNA dysregulation

Leukemia:

• miR-17-92 is overexpressed in B cell lymphoma, acute lymphoid, and myeloid leukemias  

• MiR-17-92 is needed for developing blood cells to divide – as they mature miR-17-92 decreases and Egr2 increases  

• Egr2 tells cells to stop dividing and mature

• if there is too much miR-17-92, Egr2 is not enough to stop it --> lots of miR-17-92 activates unwanted proliferation --> cancerous  

hemophilia

• clotting disorder, easy bleeding, spontaneous internal bleeding  

• Transposons --> insertional mutagenesis  

• Retrotransposon insertion --> mutation in factor VIII gene --> hemophilia A --> excessive bleeding  

other transposon related conditions

• neurofibromatosis

• breast/ovarian cancer due to mutations in BRCA2 gene

peripheral neuropathies

• PNS is affected – sensory and motor segment  

• tRNA mutations in the mitochondrial tRNA  

• Rare: MELAs (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes) and mitochondrial myopathy  

Charcot Marie Tooth disease inheritance

most common inherited neuropathy (1 in 2500)

Charcot Marie Tooth genetic mechanism

• Mutation in the aminoacyl-tRNA synthetase (aaRS) 

• Translation: ribosomes read codon, tRNA has to come with anticodon  

• aaRS charges the tRNA 

• aaRS not functioning --> tRNA not charged --> protein synthesis is stopped --> no protein production 

• Disproportionately stresses long peripheral axons --> axonal degeneration --> motor and sensory neuropathy  

Charcot Marie Tooth clinical features

• Loss of muscle bulk and weakness in legs, ankles, feet 

• Curled toes  

• Pes cavus (high arched foot)  

• Decreased ability to run  

• Foot drop, gait change  

• Frequent tripping or falling  

• Decreased sensation or loss of feeling in legs and feet  

• Weakness from lower limbs and can spread upwards  

• Loss of nerve supply --> cells can atrophy – denervation atrophy  

• Stark-bird or inverted champagne bottle-like legs  

• Symptoms vary from person to person, longevity is not affected, but QOL is reduced  

Huntington disease mutation

mutation in the gene Huntingtin --> increased CAG repeats in DNA and mRNA when HTT gene is transcribed  

• CAG repeats >35  

• 27-35: intermediate – they don’t have it but next generation does  

• <27 is normal

huntington’s pattern of inheritance

autosomal dominant

huntington’s age of onset

symptoms noticeable btwn ages 35-45

huntington’s genetic mechanism

CAG repeats 

Huntington’s clinical features

• Adult-onset degeneration of the basal ganglia --> progressive neurologic symptoms  

• Basal ganglia is responsible for cognition, emotion, and fine tuning movement 

• Dance-like movement – Huntington chorea  

• Progressive neurologic problems  

• Pass away in 15-20 years  

Diamond Blackfan anemia mutation

RPS19 and RPS24 --> impair pre-rRNA processing of the 18S rRNA --> decreased production of the 40S ribosomal subunit  

• (18S rRNA is the functional core of 40S ribosomal subunit)  

• (breakdown in ribosome biogenesis places severe stress on rapidly dividing cells, specifically, erythroid progenitor cells)  

Diamond Blackfan anemia pattern of inheritance

AD/sporadic - not possible to get during adulthood  

Diamond Blackfan anemia hematological features

hypo-productive anemia, often with macrocytosis  

• 90% of kids with severe anemic features within 1 year of life: pale, breathing difficulty, palpitation, swallowing issue, not enough energy  

• Bone marrow: normocellular marrow with reduced erythrocyte precursors  

• Macrocytosis because cells don’t do proper cell division  

• red cell aplasia: significant reduction in erythrocyte precursors, increased sensitivity to heme

• Increased HbF, increase EPO: stressed hematopoiesis

• Ask kidney to increase EPO to produce more RBC  

• Increase fetal Hb: not very effective – high affinity for O2, not as efficient at delivering O2  

•  increased erythrocyte ADA: enzyme that participates in purine metabolism  

Diamond blackfan non-hematological features

• Skeletal: short stature, small head, short forehead with short hairline, wide eyes, flat bridge on nose, triphalangeal thumb  

• Variable penetrance  

Diamond Blackfan Treatment

Corticosteroids improve erythropoiesis and blood transfusion with iron chelation  

MDS with del (5 q)

• Myodysplastic: abnormality of hematopoietic stem cells --> abnormal maturation of myeloid cells (forms all cells other than lymphocytes and NK cells)  

• Not maturing normally  

MDS with del (5 q) mutation

deletion of 5q – block in erythroid differentiation 

• A part of the long arm of the 5^th chromosome is deleted  

• 5q32-q33 --> SPARC, RPS14, and several miRNA genes  

• SPARC: tumor suppressor gene --> increased risk for cancer – acute myeloid leukemia --> lifespan is 18 mos after diagnosis  

• RPS14: smaller ribosomal subunit – maturation of RBCs blocked, macrocytic anemia  

• MiRNA genes: platelet structure is affected  

• Micro-megakaryocytes: small platelets  

• Hypo-lobulated = <8 lobules  

MDS with del (5 q) mutation pattern of inheritance

sporadic mutation after conception; no family history – acquired in adulthood  

• Somatic: restricted to a specific organ – hematopoietic stem cells  

MDS with del (5 q) clinical features

• Severe macrocytic anemia  

• Normal/elevated platelets with hypo lobulated micro-megakaryocytes  

• Relatively low rate of progression to AML  

 

Lenalidomide

increased erythropoiesis, modulation of cytokine production, inhibition of phosphates  

Decrease of CK1alpha protein (tumor cells are dependent on this kinase) - (triggers p53 dependent apoptosis of malignant cells) 

treatment MDS with del (5q)

blood transfusion, lenalidomide

• corticosteroids will not be helpful