3D trajectories adopted by coding and regulatory DNA elements: first-passage times for genomic interactions

Area of Science:

• Immunology
• Molecular Biology
• Biophysics

Background:

• B lymphocyte development requires the assembly of immunoglobulin heavy-chain variable (VH), diversity (DH), and joining (JH) gene segments to create a diverse antigen receptor repertoire.
• Understanding the three-dimensional (3D) organization and dynamics of these genomic elements within the nucleus is crucial for deciphering the mechanisms of V(D)J recombination.

Purpose of the Study:

• To investigate the 3D trajectories and dynamics of VH and DH-JH-Emicro regions during B lymphocyte development.
• To model the movement of these genomic elements and identify factors influencing their interactions.

Main Methods:

• Marking distal VH and DH-JH-Emicro regions with Tet-operator binding sites in pro-B cells.
• Tracing the 3D trajectories of these marked regions using live-cell imaging in cells expressing Tet-repressor-EGFP.
• Applying fractional Langevin dynamics (fLm) modeling to analyze the observed motion and interactions.

Main Results:

• The VH and DH-JH-Emicro elements exhibited fractional Langevin motion, indicative of viscoelastic hindrance from the nuclear environment.
• Fractional Langevin dynamics modeling predicted a high probability of DHJH elements encountering VH elements within minutes.
• Spatial confinement was identified as the primary factor controlling the frequency of these crucial genomic encounters.

Conclusions:

• The viscoelastic properties of the nucleus influence the dynamic behavior of immunoglobulin gene segments during development.
• Spatial confinement of topological domains plays a significant role in regulating the timing of essential genomic interactions for V(D)J recombination.