Disorders of Nucleotide Expansion and Splicing 2

Question 1

Spinal Muscular Atrophy normal vs. pathologic

Answer 1

Have 2 SMN genes with identical AA sequences - normal

Deletion of SMN1, leaving only SMN2 active

Question 2

Severity of SMA releated to

Answer 2

AMount of exon 7 conatined in SMN portein

Question 3

SMA mutation

Answer 3

T for C in exon 7 of SMN1…causes omission of exon 7…changes ESE to ESS

Question 4

Role of SMN in the cell

Answer 4

Assembly of snRNPs

Question 5

DMD mutation

Answer 5

A for T in exon 31 of dystrophin…causes omission of exon 31…creates stop codon and ESS signal…sometimes exon including stop codon is skipped so the protein is mildly functional vs. truncated

Question 6

Frontal temporal dementia with parkinsonism mutation

Answer 6

Normally 4R tau=3R tau

Amplication of ESE in exon 10 of MAPT (chromosome 17)…leads to more 4R tau and less 3R tau

Question 7

CF mutation

Answer 7

most commonly exon 10 deletion of phenylalanine…changes in number of

Question 8

CF exon 9 inclusion

Answer 8

Affects phenotype expressivity…mild disease if exon 9 present, severe if absent…determined by (UG)m(U)n

Question 9

Antisense oligonucleotide tx

Answer 9

Bind to target ESS and conjugated to proteins containing an ESE element. Basically replace a silencer with an enhancer…encourages retention of desired exon in final transcript.

Question 10

snRNAs as vehicle for antisense RNA

Answer 10

Will cause skipping of stop codon exon…leads to partially functional

Question 11

RNAi will

Answer 11

Degrade the protein

Question 12

Hairpins drive

Answer 12

Expansions and contractions

Question 13

Mechanism of DM1

Answer 13

CUG repeat expansion in the 3’UTR of the DMPK gene…causes formation that sequester MBNL1 and upregulates CELF1 (a CUG binding protein)

Question 14

MIssplicing examples in myotonic dystrophy

Answer 14

Missplicing of CLCN1 results in NMD and IR alpha missplicing causes insulin resistance

Question 15

Accumulations of DM

Answer 15

Are in the nucleus composed of proteins and mRNA

Question 16

Spinocerebellar ataxia 8 mutation

Answer 16

CTG expansion in noncoding RNA

Question 17

Mechanism of SCA8

Answer 17

Antisense transcript to CTG becomes polyglutamine repeats that accumulate in the cerebellum

Question 18

Sequestrian hypothesis

Answer 18

Normal binding proteins such as MBNL1 that help splicing are sequestered to hairpin structures and prevents them from working on regular proteins

Question 19

Over expression of MBNL

Answer 19

Rescues phenotypes of DM

Question 20

DMPK protein is a

Answer 20

protein kinase

Question 21

Cis effects of DM1

Answer 21

Haploinsufficiency due to less DMPK protein…local disruption of chromatin…dz is mostly trans-dominant

Question 22

FXTAS mutation

Answer 22

In FMR1 mRNA with CGG repeats

Question 23

FXTAS sources of toxicity

Answer 23

1) Sequestration of RNA binding proteins

2) Irregular translation of short peptides that are toxic

Question 24

FXTAS DNA repair

Answer 24

DNA damage repair is overtaxed and therefore not as effective

Question 25

ALS haploinsufficiency

Answer 25

Reduced expression of a given gene

Question 26

Gain of function ALS

Answer 26

Formation of aggregates of RNA and sequestering of proteins

Question 27

ALS also has

Answer 27

Abnormal bidirectional transcription of the expanded repeat sequences followed by RAN translation into dipeptide protein repeat proteins (DPRs)

Question 28

Therapeutic targets

Answer 28

1) MBNL1 overexpression via adenovirus
2) PKC inhibition via hyperphosphorylation of CELF1
3) Toxic RNA silencing using siRNA or ASOs to create degradation
4) Toxic RNA targeted for binding to eliminate ineraction with RNA binding proteins or small molecules using ASOs
5) Toxic RNA bound by small molecules to induce relaxation and release MBNL1

Question 29

Trans-dominant disorders

Answer 29

Controls expression of a gene on another chromosome

Question 30

Cis-dominant disorders

Answer 30

Where gene activity affected in same chromosome of mutation

Question 31

DM1 loss and gain of function

Answer 31

Loss - MBNL1

Gain - CELF1