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Spring 2022 > BIOL 435 Ch. 6 Part Two (Organization+Expression of Lymphocyte Receptor Genes) > Flashcards

BIOL 435 Ch. 6 Part Two (Organization+Expression of Lymphocyte Receptor Genes) Flashcards

1
Q

recombination among various V gene segments

A
  • generates a diverse repertorie of Ab combining sites

- 2.3x10^6

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2
Q

heavy chain rearranged

A
  • first
  • if functional, it will be expressed on Pre-B cells with a surrogate light chain (gamma5 and VPreB)
  • Pre-B cell undergoes several rounds of replication
  • light chain rearrangement then begins in each daughter cell
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3
Q

how does recombination of heavy chain increase diversity?

A

-each daughter cell has same heavy chain but a different light chain can be added
>4 possibilities

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4
Q

recombination is directed by

A

-signal sequences

>RSS

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5
Q

recombination signal sequences (RSS)

A
  • flank each Ab gene segment
  • each has a conserved nonamer (9) and heptamer (7) sequence
  • in between the nonamer/heptamer lies either a 12 or 23 bp spacer sequence
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6
Q

12/23 rule

A

-spacing and arrangement dictates that a 12bp RSS must pair with a 23bp RSS for recombination to occur

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7
Q

gene segments are joined by

A

-RAG1/2 recombinase

>both proteins are needed for recombination

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8
Q

RAG

A

-recombination activating gene

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9
Q

RAG1

A
  • more important

- it forms a complex with RSSs stabilized by binding RAG2

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10
Q

RAG1/2 complex

A

-responsible for recognizing and cutting DNA at the immuonglobin-encoding region and the RSS

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11
Q

numerous other proteins are required for recombination

A

-including several that are not unique to lymphocytes

>non-homologous recombination proteins

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12
Q

V(D)J recombination

A
  • occurs in a series of well-defined steps
    1. RAG proteins bind to RSSs and cleave the DNA
    2. Other proteins process the hairpin loops that form after RAG reacts
    3. Products that will later be degraded
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13
Q

products from V(D)J recombination

A
  • recombined coding joint
  • leftover signal joint
  • will later be degraded
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14
Q

simple steps V(D)J H. chain recombination

A
  1. Germline configuration
  2. D to J recombination
  3. V to DJ recombination
  4. Transcription
  5. Splicing: mRNA
  6. Polypeptide chain
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15
Q

simple steps V(D)J L. chain recombination

A
  1. Germline DNA
  2. V to J recombination
  3. Transcription
  4. Splicing
  5. Polypeptide chain
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16
Q

timeline for B-cells

A
  1. Early pro-B cell
  2. Late pro-B cell
  3. Pre-B cell
  4. Immature B-cell
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17
Q

early pro-B cell

A
  • H-chain gene rearrangement

- D-J rearrangements on both chromosomes

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18
Q

late pro-B cell

A

-H-chain gene rearrangement
-V-DJ rearrangement on 1st chromosome
>if NOT good: V-DJ rearrangement on 2nd chromosome
»if NOT good: apoptosis

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19
Q

pre-B cell

A

-L-chain gene rearrangement
-rearrange 1st L. chain gene on 1st chromosome
>go through all 4 if need be
»if none good: apoptosis

20
Q

immature B-cell

A
  • rearrangement ceases

- cell expresses IgM lambda/kappa

21
Q

mice L. chain

A

-try kappa first

22
Q

length of helix 12/23

A
  • related to turn
  • 12=1 turn
  • 23=2 turns
23
Q

unproductive rearrangements

A

-recombined V-segments where trimming caused loss of correct reading frame
>cannot encode Ab moleculesV0

24
Q

unproductive rearrangements

A

-recombined V-segments where trimming caused loss of correct reading frame
>cannot encode Ab molecules

25
Q

V(D)J recombination direction

A
  • can occur between segments transcirbed in either same or opposite directions
  • as long as RSSs lined up, actual orientation of gene is irrelevant
26
Q

5 mechanisms generate diversity in naive B-cells

A
  1. Inherit multiple V, D, and J gene segments
  2. Recombine gene segments
  3. Random assortment
  4. Recombination inaccuracy
  5. Somatic hypermutation
27
Q

recombine gene segments

A

-which gene segments are put together

28
Q

random assortment

A

-H/L chain combinational diversity (kappa or lambda)

29
Q

recombinational inaccuracy types

A
  1. P-nucleotide addition
  2. Exonuclease timing (mostly H-chain)
  3. N-nucleotide addition (mostly H-chain)
30
Q

P-nucleotide addition

A

-templated nucleotides additions between joints, resulting from asymmetircal cleaving of hair pin strucutres

31
Q

exonuclease trimming

A

-sometimes occurs at junctions, losing nucleoties and chaning reading frames

32
Q

N-nucleotide addition

A

-mediated by Tdt actavity in (C heavy and beta chains) adding random nucleotides between joints

33
Q

chromatin alteration

A
  • involved in regulation of V(D)J gene recombination
  • catalytic activity of RAG1/2 binding occurs in extraordinary complex nuclear environment
  • since V, D, J gene segments are spread out, higher order chromatin structure must play a role
34
Q

RAG1/2 binding affected by

A

-epigenetic modifications on histoines associated with target sequences

35
Q

histoine acetylation or methylation

A

-affects accessibility to enzymatic activity in chromatin

36
Q

rosette-containing chromatin regions

A
  • cotain accesible gene loci

- recombination events are topologically limited to genes located here

37
Q

rosette containing D, J, C heavy regions

A

-defines scope of RAG activity in earliest pre-pro-B cell precursor

38
Q

D-J heavy recombination enables

A

-loop structure alteration for V-D heavy recombination in later pro-B cell stage

39
Q

allelic exclusion

A

-ensures that each B-cell synthesizes only one heavy and one light chain

40
Q

heavy chains are

A

-recombined and expressed first
>expression of a functional H-chain shuts down recombination machinery temporarily
>paired with a surrogate L-chain (SLC) to from a pre-BCR

41
Q

if SLC will pair with H-chain

A

-machinery starts up again

>L-chain recombination takes place

42
Q

nonproductive arrangements

A

-lead to programmed cell death (apoptosis) during development

43
Q

receptor editing

A

-of potentially auto reactive receptors occurs in L-chains
-functional antibody in an immature B-cell may bind to self-Ag
>recombination machinery can be turned back on to edit and salvage rearrangement or at least inactivate it

44
Q

mature B-cells express both

A
  • IgM and IgD antibodies

* mRNA splicing mechanism is the cause

45
Q

spacer RNA sequence

A

-between VDJ and C regions
-mRNA splicing removes the intervening spacer
>leaves VDJC mRNA ready to be translated

46
Q

primary transcripts for IgM heavy chains

A

-may result from RNA polymerase transcribing through both IgM and IgD constant regions
>dependin on which C segment becomes polyadenylated, IgM or IgD could end up being produced

47
Q

mRNA splicing also controls

A
  • whether the cell produces membrane bound or secreted IgM

* always membrane bound first than differentiated

Spring 2022 (54 decks)

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