[Paper Review] On The Organization Of Human T Cell Receptor Loci

Amir A. Toor, Abdullah A. Toor+1 more|arXiv (Cornell University)|Jan 4, 2015

T-cell and B-cell Immunology36 references4 citations

TL;DR

This study proposes that the human T cell receptor (TCR) loci exhibit a log-periodic organization, where V, D, and J gene segments are arranged in a self-similar, logarithmically scaled pattern across the DNA. Using logarithmic transformation and angular coordinate analysis of gene segment spacing, the authors demonstrate that this structural organization correlates with periodic variation in T cell clonal frequencies, suggesting that DNA helix geometry may influence recombination probability through interference effects.

ABSTRACT

The human T cell repertoire is generated by the rearrangement of variable (V), diversity (D) and joining (J) segments on the T cell receptor (TCR) loci. To determine whether the structural ordering of these gene segments on the TCR loci contributes to the observed clonal frequencies, the TCR loci were examined for self-similarity and periodicity in terms of gene segment organization. Logarithmic transformation of numeric sequence order demonstrated that the V and J gene segments for both T cell receptor alpha (TRA) and beta (TRB) loci were arranged in a self-similar manner when the spacing between adjacent segments was considered as a function of the size of the neighboring gene segment. The ratio of genomic distance between either the J (in TRA) or D (in TRB) segments and successive V segments on these loci declined logarithmically. Accounting for the gene segments occurring on helical DNA molecules, in a logarithmic distribution, sine and cosine functions of the log transformed angular coordinates of the start and stop nucleotides of successive TCR gene segments showed an ordered progression across the locus, supporting a log-periodic organization. T cell clonal frequencies, based on V and J segment usage, from three normal stem cell donors plotted against the respective segment locations on TRB locus demonstrated a periodic variation. We hypothesize that this quasi-periodic variation in T cell clonal repertoire may be influenced by the location of the gene segments on the logarithmically scaled TCR loci. Interactions between the two strands of DNA in the double helix may influence the probability of gene segment usage by means of either constructive or destructive interference resulting from the superposition of the two helices, impacting probability of DNA recombination.

Motivation & Objective

• To investigate whether the physical organization of TCR V, D, and J gene segments on human chromosomes influences T cell repertoire diversity.
• To determine if structural ordering of gene segments contributes to observed clonal frequency patterns in T cell receptors.
• To explore whether DNA helix geometry and spatial periodicity affect recombination probability during TCR gene rearrangement.
• To model the genomic spacing of TCR segments using logarithmic and trigonometric functions to detect self-similarity and periodicity.
• To correlate segment location on the TRB locus with empirically measured T cell clonal frequencies from stem cell donors.

Proposed method

• Applied logarithmic transformation to the numeric order of TCR gene segments to assess self-similarity in spacing across TRA and TRB loci.
• Analyzed the ratio of genomic distance between J (TRB) or D (TRB) segments and successive V segments, showing a logarithmic decline.
• Mapped the start and stop nucleotides of TCR gene segments onto helical DNA coordinates and computed sine and cosine functions of their log-transformed angular positions.
• Used trigonometric functions of log-transformed angular coordinates to detect ordered, periodic progression across the TCR loci.
• Plotted T cell clonal frequencies from three normal stem cell donors against segment locations on the TRB locus to identify periodic trends.
• Proposed that constructive or destructive interference from DNA double helix superposition may modulate recombination probability based on segment location.

Experimental results

Research questions

• RQ1 Does the spatial arrangement of V, D, and J segments on human TCR loci exhibit self-similarity or periodicity?
• RQ2 Is there a correlation between the logarithmic scaling of gene segment spacing and observed T cell clonal frequencies?
• RQ3 Can the organization of TCR loci be described using trigonometric functions of log-transformed angular coordinates?
• RQ4 Does DNA helix geometry influence the probability of TCR gene segment recombination through interference effects?
• RQ5 To what extent does the position of a gene segment on the TCR locus predict its usage frequency in the T cell repertoire?

Key findings

• The ratio of genomic distance between J or D segments and successive V segments on TRA and TRB loci declined logarithmically with segment order.
• Logarithmic transformation of gene segment order revealed self-similar patterns in the organization of V and J segments across both TRA and TRB loci.
• Sine and cosine functions of log-transformed angular coordinates of TCR gene segment boundaries showed a consistent, ordered progression across the loci.
• T cell clonal frequencies from three normal stem cell donors exhibited periodic variation when plotted against segment location on the TRB locus.
• The observed periodicity in clonal frequencies correlates with the log-periodic organization of gene segments on the TCR loci.
• The study suggests that DNA double helix interactions may modulate recombination probability via constructive or destructive interference based on segment position.