Isoforms of terminal deoxynucleotidyltransferase: developmental aspects and function

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• The adaptive immune system relies on T-cell receptors (TCRs) and B-cell receptors (BCRs) for antigen recognition.
• Recombination-activating gene (RAG) and nonhomologous end-joining (NHEJ) proteins are essential for V(D)J recombination, but contribute limited diversity.
• Nontemplated nucleotide addition by terminal deoxynucleotidyltransferase (TdT) is a major driver of CDR3 diversity in TCRs and BCRs.

Purpose of the Study:

• To investigate the distinct functional roles of different terminal deoxynucleotidyltransferase (TdT) isoforms in lymphocyte development.
• To elucidate how TdT splice variants contribute to the diversification of T-cell and B-cell receptor repertoires.

Main Methods:

• Analysis of alternative mRNA splicing of TdT in mammals.
• Characterization of enzymatic activities (nucleotide addition and exonuclease) of TdT splice variants.
• Assessment of the impact of TdT isoforms on V(D)J junctional sequences in T-cell and B-cell receptor genes.

Main Results:

• Terminal deoxynucleotidyltransferase (TdT) exists in multiple isoforms due to alternative mRNA splicing.
• The short form (TdTS) catalyzes nontemplated nucleotide addition during V(D)J recombination.
• Longer isoforms (TdTL1, TdTL2) possess 3' to 5' exonuclease activity, leading to nucleotide deletion.

Conclusions:

• Splice variants of TdT have opposing enzymatic functions, influencing lymphocyte repertoire diversity.
• The differential activities of TdT isoforms are critical for shaping the composition and length of V(D)J gene segments.
• TdT's enzymatic activities are essential for generating the broad diversity of antibodies and T-cell receptors.