Feb. 19th (Exam 2) Flashcards
What is the first general phase of B-cell development?
- Repertoire assembly in the bone marrow
What distinguishes undifferentiated precursor/progenitor cells?
What is present on all hematopoietic stem cells?
Cell-surface markers
CD34
What are Pro-B cells?
Can they still self renew?
These are the earliest identifiable cells of the B-cell lineage.
They have retained a limited capacity for self-renewal and can make other pro-B cells and cells that further develop.
What is the stroma?
This is the supportive cells and connective tissue of any organ.
What do bone marrow stromal cells do?
- They interact with the developing B cells through adhesion molecules.
- They produce growth factors that act on the attached B cells.
What was the example of the adhesion molecule that we saw holding B cells to the bone marrow?
What was the growth factor that is produced on the surface of bone marrow stromal cells that binds to the B cells?
What on the B cells allows for this?
What is the cytokine secreted by the bone marrow stromal cells that acts on Late Pro-B cells and Pre-B cells?
CAM - Cell Adhesion Molecule
SCF (Membrane bound Stem Cell Factor) binds to Kit
Interleukin 7 or IL-7
Where do the most immature B-cells reside in regards to the bone marrow stromal cells?
Sub Endosteum
Where do maturing bone marrow cells go?
Towards the central axis (interior surface) - they don’t need as much contact with the surrounding stromal
What makes gene rearrangement inherently imprecise and inefficient?
Explain.
The addition of P and N nucleotides during the junction of heavy chain parts (junctional diversity)
These additions can shift the reading frame so bad that it does not code for a functional heavy chain.
For each junction what are the chances that we maintain the correct reading frame?
33%
!!!
What is a non-productive rearrangement?
A non-productive rearrangement happens when there is a gene rearrangement that results in a non-functional protein.
What is one advantage we have against those horrible odds of 1/3 being faulty?
Every B cell has two copies of the immunoglobulin heavy-chain locus.
So… if one of the rearrangements on chromosome n is bad, the cell may still have a chance to complete another rearrangement on the homologous chromosome.
What happens if negative rearrangements are made on both homologous chromosomes?
The cell will certainly undergo apoptosis.
What are E2A and EBF?
What do they do?
When are they used to turn stuff on?
They are transcription factors.
- They are responsible for the transcription of Pax-5 TF
- RAG 1+2
- . VpreB and 5 surrogate light chains
TFs active in early-pro B cells.
What is Pax-5?
What does it do?
It is a transcription factor that is turned on by E2A and EBF.
- Responsible for transcription of the Ig(alpha)
- Responsible for transcription of cell surface protein CD19
- Also helps transcribe the surrogate chains
TF is used in the late pro B cell
Why is the first rearrangement event joining the heavy D and J segments relatively efficient?
Because no matter where D ends up getting attached to the J segment, can be read (transcribed) no matter how it is attached - it works no matter which reading frame we are in.
What is the default for B cells in development?
What is needed for survival and continued differentiation?
Define this.
Apoptosis
Survival Signals
Survival Signals are positive signals for survival and further differentiation.
How many of the Early Pro-B cells make it to the Late Pro-B cell stage?
How many of the Late Pro-B cells make it to the Large Pre-B cell phase?
- Most of them make it because D-J rearrangement is pretty good.
- Only 50% make it because of non-productive rearrangements.
What are the criteria that a Pro-B cell must satisfy before it is allowed to become a Pre-B cell?
- They must make a mu heavy chain
- They must be able to demonstrate the ability of the mu heavy chain to combine with an immunoglobulin light chain.
How does a Late Pro-B cell demonstrate the ability to bind its newly made heavy chain (mu) with a light chain if there are no light chains yet?
There are separate genes that are used as Surrogate Light Chains.
Surrogate Light Chains are made up of two proteins whose genes are found at different loci and are conventional and require no rearrangement:
- VpreB - pseudo variable region
- Lambda 5 pseudo constant region
What all happens within the ER of the Late pro-B cell?
The heavy chain that was just made has a chance to combine with VpreB and Lambda 5 and Ig(beta)-Ig(alpha) to form a complex that looks similar to that of the B-cell Receptor
This is called the Pre-B cell receptor
What is the job of Ig-(beta)?
Survival Signals
It acts as a pathway for signal transduction (from the complete pre-B cell receptor) to shut down the gene rearrangement of the immunoglobulin heavy chain.
It also drives the Late Pro-B cell into several rounds of cell division that give rise to a clonal population of pre-B cells.
Once the DNA that contains the VDJ rearranged sequence through the C (mu), how does the mRNA get cleaned up so that it can become a functional heavy chain within the ER?
It is cleaned up via RNA splicing.
How is allelic exclusion ensured in Late Pro-B cells transitioning to Large Pre-B cells
- There needs to be proper Pre-B cell Receptor assembly.
- Ig (beta) acts as a signal transducer to signal for the RAG gene to stop being transcribed
- Ig (beta) acts as a signal transducer for the RAG protein to be degraded
- Ig (beta) acts a signal transducer to restructure the chromatin of the heavy chain locus.
