Cellular and Molecular Biology and Immunology

Basic Sciences 2023, Jan, 25 | 12:00 am

Cellular and Molecular Biology and Immunology

Chromosomes
- 46 chromosomes in 23 pairs: 22 pairs of autosomes, 1 pair of sex chromosomes
- Composed of DNA coiled around histone proteins
  - DNA has a double-helix structure with linked nucleotides (adenine linked to thymine; guanine linked to cytosine) on a sugar-phosphate backbone
  - Three nucleotides = 1 codon, which corresponds to one amino acid
    
    FIG. 1.47 DNA information is transcribed into RNA in the nucleus. Messenger RNA is then transported to the cytoplasm, where ribosomes complete translation into proteins.
    
    From Jorde LB et al, editors: Medical genetics, ed 2, St Louis, 1999, Mosby.
  - String of codons code for a string of amino acids = protein
  - Gene: a section of DNA that codes for one protein

Transcription—DNA to mRNA ( Fig. 1.47 )

Unwinding of DNA for transcription occurs by DNA topoisomerase.
- Topoisomerase-1 (scl-70) antibodies are seen in scleroderma and CREST (calcinosis, Raynaud phenomenon, sclerodactyly, telangiectasia) syndrome.
RNA polymerase “reads” unwound DNA and builds corresponding mRNA
- RNA: single-stranded ribose sugar composed of nucleotides adenine, guanine, cytosine, and uracil
- Uracil in RNA links to adenine of DNA because there is no thymine in RNA
Posttranscription modification
- Exons are regions of DNA that code for mRNA (mnemonic: EXons are EXpressed).
- Introns are regions of DNA that are between exons; 97% of the human genome consists of noncoding DNA.
- Splicing is the processing and removal of introns along with the combining of exons to make final mRNA used in translation.
  - Small nuclear ribonucleoproteins (snRNPs) are RNA-protein complexes that mediate this posttranscriptional modification.
  - Examples of these proteins are the U1 and Smith proteins.
    - Anti-Smith antibodies are specific to SLE.
    - Anti–U1-RNP antibodies are seen in mixed connective tissue disease.
Translation (see Fig. 1.47)
- Building of a protein out of amino acids from mRNA template
  - Transfer RNA carries a specific amino acid to the ribosome, based on the mRNA codon.
    - Antibodies to tRNA synthetase (anti–Jo-1 antibodies) are seen in
      
      dermatomyositis.
Cell cycle and ploidy
Genetics

Ploidy is the number of sets of chromosomes in a cell annotated by XN.
The cell cycle entails the events within a cell that result in DNA duplication, with production of two daughter cells.
- Growth 0 (G0)—stable phase of cells with diploid (2N) DNA content
- Growth 1 (G1)—upon stimulus, cells begin growth but remain diploid (2N).
- Synthesis (S)—period of DNA replication resulting in tetraploidy (4N)
- Growth 2 (G2)—phase of cell growth and protein synthesis that is tetraploid (4N) throughout
- Mitosis (M)—sequence of events that result in two identical daughter cells that are each 2N
  - Separation of chromosomal material for daughter cells occurs by spindle fibers’ attachment to centromeres that link sister chromatids
    - Anticentromere antibodies are seen in CREST syndrome.
Certain proteins regulate progression through the cell cycle. Genetic defects and alterations of these tumor suppressor proteins can predispose a cell to dysregulated growth.
- pRb-1 (retinoblastoma protein) undergoes progressive cell cycle–regulated phosphorylation.
  - Targets E2F, a transcription factor that regulates genes important for cell cycle control.
  - Implicated in retinoblastoma and osteosarcoma
- p53—prevents entry to S phase
  - Implicated in osteosarcoma, rhabdomyosarcoma, and chondrosarcoma

Mendelian inheritance
- Due to transmission of alleles to offspring
  - Phenotype refers to the features (traits) exhibited because of genetic makeup (genotype).
Mendelian traits may be inherited by one of four modes (Tables 1.30

and 1.31).
- Autosomal dominant (AD)
  - Involves a gene on an autosomal chromosome; one of the two alleles for the chromosome pair must be abnormal for the disease phenotype to occur.
  - Examples: syndactyly/polydactyly, Marfan syndrome, hereditary multiple exostoses (HME), malignant hyperthermia, Ehlers-Danlos syndrome, achondroplasia, osteogenesis imperfecta (types I and IV)
- Autosomal recessive (AR) (most enzyme/biochemical deficiencies)
  - Involves a gene on an autosomal chromosome; both alleles for the chromosome pair must be abnormal for the disease phenotype to occur.
    - Example: diastrophic dysplasia, due to a mutation in the DTDST (SLC26A2) gene on chromosome 5 that encodes for a sulfate transport protein
- X-linked dominant

Table 1.30

Mendelian Inheritance

Inheritance Pattern

Description

Punnett Square(s)

Autosomal

Autosomal dominant disorders typically represent structural defects.

Disorder is manifested in the heterozygous state (Aa).

Affects 50% of offspring (assuming only one parent is affected)

Normal offspring do not transmit the condition.

There is no gender preference.

dominant•

A is the

mutant

dominant

allele.

Autosomal recessive•

Autosomal recessive disorders typically represent biochemical or

a is the

enzymatic defects.

mutant

recessive allele.

Disorder is manifested in the

homozygous state (aa).

Parents are unaffected (they are most commonly heterozygotes).

Affects 25% of offspring (assuming each parent is a heterozygote).

There is no gender preference.

X-linked

dominant• X′ is the mutant dominant X allele.

X-linked dominant disorders are manifested in the heterozygous state (X′X or X′Y).

Affected female (mating with unaffected male) transmits the X-linked gene to 50% of daughters and 50% of sons.

Affected male (mating with unaffected female) transmits the X-linked gene to all daughters and no sons.

X-linked

recessive• X is the mutant recessive X allele.

Heterozygote (X′Y) male manifests the condition.

Heterozygote (X′X) female is unaffected.

Affected male (mating with unaffected female) transmits the X-linked gene to all daughters (who are carriers) and no sons.

Carrier female (mating with unaffected male) transmits the X-linked gene to 50% of daughters (who are carriers) and 50% of sons (who are affected).

Table 1.31

Comprehensive Compilation of Inheritance Pattern, Defect, and Associated Gene in Musculoskeletal Disorders

Disorder Inheritance Pattern Defect Associated Gene
Dysplasias
Achondroplasia	Autosomal dominant	Defect in the fibroblast growth factor receptor 3	FGF3R
Diastrophic dysplasia	Autosomal recessive	Mutation of a gene coding for a sulfate transport protein	DTDST
Kniest dysplasia	Autosomal dominant	Defect in type II collagen	COL 2A1
Laron dysplasia (pituitary dwarfism)	Autosomal recessive	Defect in the growth hormone

		receptor
McCune-Albright syndrome (polyostotic fibrous dysplasia, café-au-lait spots, precocious puberty)	Sporadic mutation	Germline defect in the Gsα protein	Mutation of Gsα subunit of th receptor/aden cyclase–coup G proteins
Metaphyseal chondrodysplasia:
Jansen form	Autosomal dominant		PTH; PTH-related protein
McKusick form	Autosomal recessive		RMRP
Schmid-tarda form	Autosomal dominant	Defect in type X collagen	COL 10A1
Multiple epiphyseal dysplasia	Autosomal dominant (most commonly)	Cartilage oligomeric matrix protein	COMP
Spondyloepiphyseal dysplasia	Autosomal dominant (congenita form) X-linked recessive (tarda form)	Defect in type II collagen	Linked to Xp22.1 p22.31, SEDL (tarda), and C 2A1 (congenit
Achondrogenesis	Autosomal recessive	Fetal cartilage fails to mature
Apert syndrome	Sporadic mutation/autosomal dominant		FGF2R
Chondrodysplasia punctata
Conradi-Hünerman	Autosomal dominant
Rhizomelic form	Autosomal recessive	Defect in subcellular organelles (peroxisomes)
Cleidocranial dysplasia (dysostosis)	Autosomal dominant	Mutation of a gene coding for a protein related to	CBFA1

		osteoblast function
Dysplasia epiphysealis hemimelica (Trevor disease)	Unknown
Ellis–van Creveld syndrome (chondroectodermal dysplasia)	Autosomal recessive		EVC
Table Conti

Disorder Inheritance Pattern Defect Associa
Fibrodysplasia ossificans progressiva	Sporadic mutation/autosomal dominant
Geroderma osteodysplastica (Walt Disney dwarfism)	Autosomal recessive
Grebe chondrodysplasia	Autosomal recessive
Hypochondroplasia	Sporadic mutation/autosomal dominant	FGF3R
Kabuki makeup syndrome	Sporadic mutation
Mesomelic dysplasia (Langer type)	Autosomal recessive
Mesomelic dysplasia
Nievergelt type	Autosomal dominant
Reinhardt-Pfeiffer type	Autosomal dominant
Werner type	Autosomal dominant
Metatrophic dysplasia	Autosomal recessive
Progressive diaphyseal dysplasia (Camurati-Engelmann disease)	Autosomal dominant
Pseudoachondroplastic dysplasia	Autosomal dominant	COMP
Pyknodysostosis	Autosomal recessive
Spondylometaphyseal chondrodysplasia	Autosomal dominant

Spondylothoracic dysplasia (Jarcho-Levin syndrome)	Autosomal recessive
Thanatophoric dwarfism	Autosomal dominant		FGF3R
Tooth-and-nail syndrome	Autosomal dominant
Treacher Collins syndrome (mandibulofacial dysostosis)	Autosomal dominant
Metabolic Bone Diseases
Hereditary vitamin D–dependent rickets	Autosomal recessive	See Table 1.16
Hypophosphatasia	Autosomal recessive	See Table 1.16	PHEX
Hypophosphatemic rickets (vitamin D–resistant rickets)	X-linked dominant	See Table 1.16	PHEX
Osteogenesis imperfecta	Autosomal dominant (types I and IV) Autosomal recessive (types II and III)	Defect in type I collagen (abnormal cross-linking)	COL IA IA2
Albright hereditary osteodystrophy (pseudohypoparathyroidism)	Uncertain	PTH has no effect at the target cells (in the kidney, bone, and intestine)
Infantile cortical hyperostosis (Caffey disease)	Unknown
Ochronosis (alkaptonuria)	Autosomal recessive	Defect in the homogentisic acid oxidase system
Osteopetrosis	Autosomal dominant (mild, tarda form) Autosomal recessive (infantile, malignant form)		CLCN7,
Connective Tissue Disorders
Marfan syndrome	Autosomal dominant	Fibrillin abnormalities (some patients also have type I	FBN1 o βR2

		collagen abnormalities)
Ehlers-Danlos syndrome (there are at least 13 varieties)	Autosomal dominant (most common)	Defects in types I and III collagen have been described for some varieties; lysyl oxidase abnormalities	COL ( I c COL (
Homocystinuria	Autosomal recessive	Deficiency of the enzyme cystathionine β-synthase
Mucopolysaccharidosis
Hunter syndrome (gargoylism)	X-linked recessive
Hurler syndrome	Autosomal recessive	Deficiency of the enzyme α-L-iduronidase
Maroteaux-Lamy syndrome	Autosomal recessive
Morquio syndrome	Autosomal recessive
Sanfilippo syndrome	Autosomal recessive
Scheie syndrome	Autosomal recessive	Deficiency of the enzyme α-L-iduronidase
Muscular Dystrophies
Duchenne muscular dystrophy	X-linked recessive	Defect on the short arm of the X chromosome	Dystrop
Becker dystrophy	X-linked recessive
Fascioscapulohumeral dystrophy	Autosomal dominant
Limb-girdle dystrophy	Autosomal recessive
Steinert disease (myotonic dystrophy)	Autosomal dominant
Table C

Disorder

Inheritance

Defect

Associated Gene

Pattern
Hematologic Disorders
Hemophilia (A and B)	X-linked recessive	Hemophilia A: factor VIII deficiency Hemophilia B: factor IX deficiency
Sickle cell anemia	Autosomal recessive	Hemoglobin abnormality (presence of hemoglobin S)
Gaucher disease	Autosomal recessive	Deficient activity of the enzyme β-glucosidase (glucocerebrosidase)
Hemochromatosis	Autosomal recessive
Niemann-Pick disease	Autosomal recessive	Accumulation of sphingomyelin in cellular lysosomes
Smith-Lemli-Opitz syndrome	Uncertain
Thalassemia	Autosomal recessive	Abnormal production of hemoglobin A
von Willebrand disease	Autosomal dominant
Chromosomal Disorders With Musculoskeletal Abnormalities
Down syndrome		Trisomy of chromosome 21
Angelman syndrome		Chromosome 15 abnormality
Clinodactyly		Associated with many genetic anomalies, including trisomy of chromosomes 8 and 21
Edward syndrome		Trisomy of chromosome 18
Fragile X syndrome	X-linked trait (does not follow the typical		Xq27-28

	pattern of an X-linked trait)
Klinefelter syndrome (XXY)		An extra X chromosome in affected boys and men
Langer-Giedion syndrome	Sporadic mutation	Chromosome 8 abnormality
Nail-patella syndrome	Autosomal dominant		LMX1B
Patau syndrome		Trisomy of chromosome 13
Turner syndrome (XO)		One of the two X chromosomes missing in affected girls and women	SHOX
Neurologic Disorders
Charcot-Marie-Tooth disease	Autosomal dominant (most common)	Chromosome 17 defect for encoding peripheral myelin protein-22	PMP22
Congenital insensitivity to pain	Autosomal recessive
Dejerine-Sottas disease	Autosomal recessive
Friedreich ataxia	Autosomal recessive
Huntington disease	Autosomal dominant
Menkes syndrome	X-linked recessive	Inability to absorb and use copper
Pelizaeus-Merzbacher disease	X-linked recessive	Defect in the gene for proteolipid (a component of myelin)
Riley-Day syndrome	Autosomal recessive
Spinal muscular atrophy (Werdnig-Hoffman disease and Kugelberg-	Autosomal recessive

Welander disease)
Sturge-Weber syndrome	Sporadic mutation
Tay-Sachs disease	Autosomal recessive	Deficiency in the enzyme hexosaminidase A
Diseases Associated with Neoplasias
Ewing sarcoma			11;22 chromosomal translocation (EWS/FL11 fusion gene)
Multiple endocrine neoplasia (MEN):
Type I	Autosomal dominant		RET
Type II	Autosomal dominant
Type III	Autosomal dominant	Chromosome 10 abnormality
Neurofibromatosis (von Recklinghausen disease) type 1 (NF1) and type 2 (NF2)	Autosomal dominant	NF1: chromosome 17 defect; codes for neurofibromin NF2: chromosome 22 defect	NF1, NF2
Synovial sarcoma			(X;18) (p11;q11) chromosomal translocations (STT/SSX fusion gene)
Miscellaneous Disorders
Malignant hyperthermia	Autosomal dominant
Osteochondromatosis	Autosomal dominant
Postaxial polydactyly	Autosomal dominant		GLI3 (types A, A/B)

GJA1 (type IV)

Camptodactyly

Autosomal

dominant

Table Continued

Disorder Inheritance Pattern Defect Associa
Cerebrooculofacioskeletal syndrome	Autosomal recessive
Congenital contractural arachnodactyly			Fibrillin (chr 5)
Distal arthrogryposis syndrome	Autosomal dominant
Dupuytren contracture	Autosomal dominant (with partial sex limitation)
Fabry disease	X-linked recessive	Deficiency of α-galactosidase A
Fanconi pancytopenia	Autosomal recessive
Freeman-Sheldon syndrome (craniocarpotarsal dysplasia; whistling face syndrome)	Autosomal dominant Autosomal recessive
GM1 gangliosidosis	Autosomal recessive
Hereditary anonychia	Autosomal dominant
Holt-Oram syndrome	Autosomal dominant
Humeroradial synostosis	Autosomal dominant
Humeroradial synostosis	Autosomal recessive
Klippel-Feil syndrome		Faulty development of spinal segments along the embryonic neural tube
Klippel-Trénaunay-Weber syndrome	Sporadic mutation
Krabbe disease	Autosomal recessive	Deficiency of galactocerebroside β-galactosidase

Larsen syndrome	Autosomal dominant Autosomal recessive
Lesch-Nyhan disease	X-linked trait	Absence of the enzyme hypoxanthine guanine phosphoribosyl transferase
Madelung deformity	Autosomal dominant
Mannosidosis	Autosomal recessive	Deficiency of the enzyme α-mannosidase
Maple syrup urine disease	Autosomal recessive	Defective metabolism of the amino acids leucine, isoleucine, and valine
Meckel syndrome (Gruber syndrome)	Autosomal recessive
Möbius syndrome	Autosomal dominant
Mucolipidosis (oligosaccharidosis)	Autosomal recessive	A family of enzyme deficiency diseases
Multiple exostoses	Autosomal dominant		EXT r EXT
Multiple pterygium syndrome	Autosomal recessive
Noonan syndrome	Sporadic mutation
Oral-facial-digital (OFD) syndrome			OFD l OFD s a r
Osler-Weber-Rendu syndrome (hereditary hemorrhagic	Autosomal dominant

telangiectasia)
Pfeiffer syndrome (acrocephalosyndactyly)	Sporadic mutation/autosomal dominant		FGF2R
Phenylketonuria	Autosomal recessive	Enzyme deficiency characterized by the inability to convert phenylalanine to tyrosine because of a chromosome 12 abnormality
Phytanic acid storage disease	Autosomal recessive
Progeria (Hutchinson-Gilford progeria syndrome)	Autosomal dominant
Proteus syndrome	Autosomal dominant
Prune-belly syndrome	Uncertain	Localized mesodermal defect
Radioulnar synostosis	Autosomal dominant
Rett syndrome	Sporadic mutation/X-linked dominant
Roberts syndrome (pseudothalidomide syndrome)	Sporadic mutation/autosomal recessive
Russell-Silver syndrome	Sporadic mutation (possibly X-linked)
Saethre-Chotzen syndrome	Autosomal dominant
Sandhoff disease	Autosomal recessive	Enzyme deficiency of hexosaminidases A and B
Schwartz-Jampel syndrome	Autosomal recessive
Seckel syndrome (so-called bird-headed dwarfism)	Autosomal recessive
Table

Disorder

Inheritance Pattern

Defect

Associated Gene

Stickler syndrome (hereditary progressive arthroophthalmopathy)

Autosomal

dominant

Collagen

abnormality

Thrombocytopenia-aplasia of radius (TAR) syndrome	Autosomal recessive
Tarsal coalition	Autosomal dominant
Trichorhinophalangeal syndrome	Autosomal dominant
Argininemia	Autosomal recessive
Argininosuccinic aciduria	Autosomal recessive
Carbamyl phosphate synthetase deficiency	Autosomal recessive
Citrullinemia	Autosomal recessive
Ornithine transcarbamylase deficiency	X-linked
VATER association	Sporadic mutation
Werner syndrome	Autosomal recessive
Zygodactyly	Autosomal dominant

TGF-βR2, TGF-β receptor 2; VATER, vertebral defects, imperforate anus, tracheoesophageal fistula, and radial and renal dysplasia.

Example: hypophosphatemic rickets, due to PHEX

gene mutation (Xp.22)

X-linked recessive
- Examples: Duchenne and Becker muscular dystrophies, Hunter syndrome, hemophilia, spondyloepiphyseal dysplasia (SED) tarda

Nonmendelian traits may be inherited through “polygenic” transmission caused by the action of several genes
- Charcot-Marie-Tooth disease (AD, AR, and X-linked forms)
- Osteopetrosis (AD and AR)
- Osteogenesis imperfecta (AD and AR)
- Neurofibromatosis (AD and AR)
- SED (AD and X-linked)
Mutations
- Genetic disorders arise from alterations (mutations) in the
  
  genetic material.
  - Most skeletal dysplasias are single-gene mutations.
    - Collagen type I (bone) defects
      - Osteogenesis imperfecta (types I–IV)—COL1A1
        
        and COL1A2 genes
      - Ehlers-Danlos—COL5A1 and COL5A2 genes
    - Collagen type II (cartilage) defects
      - SED—COL2A1 gene, usually random mutations
Epigenetics
- Others
- Multiple epiphyseal dysplasia—COMP (cartilage oligomeric matrix protein) gene; also associated with pseudoachondroplasia)
- Marfan syndrome
  
  —FBN1 (fibrillin-1) gene
- Achondroplasia—FGFR3 (fibroblast growth factor receptor) gene
- Spinal muscular atrophy
  
  —SMN1 (survival motor neuron-1) gene
  - Genetic alterations that are not caused by mutations in DNA sequence
    - DNA methylation
    - Histone posttranslational modifications
    - Genomic imprinting (parent-of-origin phenotypes)
      - An example of genomic imprinting is the loss of a region in chromosome 15 with Prader-Willi syndrome (paternal; obesity, hypogonadism, hypotonia) and Angelman syndrome (maternal; epilepsy, tremors, smiling)
        
        Chromosomal abnormalities
        
        Disruptions in the normal arrangement or number of chromosomes
        
        Trisomy: one chromosome pair has an extra chromosome (total: 47 chromosomes)
        
        Trisomy 21 (Down syndrome)—ligamentous laxity, atlantoaxial instability, patellar and hip dislocations, severe flatfoot, and bunions
        
        Deletion: absence of a section of one chromosome (in a chromosome pair).
        
        Duplication: presence of an extra section of one chromosome (in a chromosome pair).
        
        Translocation: exchange of a portion of one chromosome with a portion of another chromosome
        
        Inversion: a broken portion of a chromosome reattaches to the same chromosome in the same location but in a reverse direction.
        
        Genetics of musculoskeletal conditions and abnormalities are summarized in Table 1.31.
        
        Techniques used to study genetic (inherited) disorders
        
        Restriction enzymes
        
        Used to cut DNA at precise, reproducible cleavage locations
        
        Identify polymorphisms (alternative gene expressions)
        
        Agarose gel electrophoresis
        
        Molecules are suspended in agarose gel that is exposed to an electric field.
        
        Molecules move through the gel according to size and polarity
        
        Southern blot: detects DNA
        
        Northern blot: detects RNA
        
        Western blot: detects protein
        
        Plasmid vectors
        
        A plasmid is a small, extrachromosomal, circular piece of DNA that replicates independently of the host DNA. Plasmids can confer antibiotic resistance between bacteria.
        
        The recombinant plasmid is inserted into a bacterium (the vector) by a process called transformation. The bacterium then produces a recombinant protein encoded by the inserted gene.
        
        Cytogenetic analysis
        
        FIG. 1.48 Innate immunity and adaptive immunity. The mechanisms of innate immunity provide the initial defense against infections. Adaptive immune responses develop later and consist of activation of lymphocytes.
        
        From Abbas AK et al: Cellular and molecular immunology, ed 6, Philadelphia, 2009, Saunders.
        
        Gross examination of chromosomes under microscope with the use of techniques of banding and fluorescent in situ hybridization
        
        Used to detect chromosomal translocations
        
        t(X;18)—in synovial sarcoma
        
        t(11;22)—in Ewing sarcoma
        
        t(2;13)—in rhabdomyosarcoma
        
        t(12;16)—in myxoid liposarcoma
        
        t(12;22)—in clear cell sarcoma
        
        Transgenic animals
        
        Bred to investigate the function of cloned genes.
        
        PCR amplification
        
        Repetitive synthesis (amplification) of a specific DNA sequence in vitro
        
        Screening DNA for gene mutations (e.g., prenatal diagnosis of sickle cell)
        
        Reverse transcription PCR (RT-PCR)
        
        Reverse transcriptase is used to “reverse transcribe” RNA to complementary DNA.
        
        Typically used to study RNA viruses
        
        Silencing RNA (siRNA)
        
        Blocks transcription of mRNA in order to study
        
        result of gene’s loss of function

Cellular and Molecular Biology and Immunology

Search in this site

Cellular and Molecular Biology and Immunology

Cellular and Molecular Biology and Immunology

Chromosomes

Three nucleotides = 1 codon, which corresponds to one amino acid

Topoisomerase-1 (scl-70) antibodies are seen in scleroderma and CREST (calcinosis, Raynaud phenomenon, sclerodactyly, telangiectasia) syndrome.

Translation (see Fig. 1.47)

Antibodies to tRNA synthetase (anti–Jo-1 antibodies) are seen in

dermatomyositis.

Genetics

Anticentromere antibodies are seen in CREST syndrome.

Implicated in retinoblastoma and osteosarcoma

Autosomal dominant (AD)

X-linked recessive

Trisomy 21 (Down syndrome)—ligamentous laxity, atlantoaxial instability, patellar and hip dislocations, severe flatfoot, and bunions

Translocation: exchange of a portion of one chromosome with a portion of another chromosome

Used to detect chromosomal translocations

t(X;18)—in synovial sarcoma

t(11;22)—in Ewing sarcoma

t(2;13)—in rhabdomyosarcoma

t(12;16)—in myxoid liposarcoma

t(12;22)—in clear cell sarcoma

Silencing RNA (siRNA)

Blocks transcription of mRNA in order to study

result of gene’s loss of function