Question

Which of the following events is not associated with the establishment of allelic exclusion of immunoglobulin heavy- chain loci?

a. active transcription of RAG1 and RAG2
b. degradation of RAG proteins
c. expression of only one productively rearranged heavy- chain locus
d. remodeling of chromatin structure of heavy-chain locus so that it resists gene rearrangement
e. formation of a functional pre-B-cell receptor.

Answer 1

The event not associated with allelic exclusion of immunoglobulin heavy-chain loci is the remodeling of chromatin structure of the heavy-chain locus so that it resists gene rearrangement, as chromatin remodeling facilitates rather than resists gene rearrangement.

Step-by-step explanation:

The event not associated with the establishment of allelic exclusion of immunoglobulin heavy-chain loci is d. remodeling of chromatin structure of heavy-chain locus so that it resists gene rearrangement. Allelic exclusion ensures that each B cell expresses a single antibody species by only producing one functional heavy-chain and one functional light-chain gene rearrangement. This is achieved through selective processes including:

1. active transcription of RAG1 and RAG2 which are crucial for the recombination process,
2. the degradation of RAG proteins after successful recombination to prevent further rearrangement,
3. expression of only one productively rearranged heavy-chain locus as per the allelic exclusion principle, and
4. the formation of a functional pre-B-cell receptor, which provides a checkpoint for the functional heavy-chain gene rearrangement.

Chromatin remodeling typically facilitates gene rearrangement rather than resisting it, which is essential for V(D)J recombination leading up to B-cell receptor diversity, and therefore is not consistent with the concept of allelic exclusion.