Research Article: Annotation of gene loci and analysis of expression diversity in sheep immunoglobulin
Abstract:
As an important livestock species, sheep exhibit remarkable environmental adaptability. Immunoglobulins, expressed by B cells, are among the most crucial effector molecules in adaptive immunity. However, systematic research on the structure and expression diversity of the sheep immunoglobulins gene loci remains limited. This study annotated the sheep IgH, Ig?, and Ig? loci based on the sheep genome assembly (ARS-UI_Ramb_v3.0). The sheep IgH is located on chromosome 18 and comprises 22 VH, 4 DH, and 6 JH. The Ig? is on chromosome 3, containing 18 V? and 4 J?. The Ig? is situated on chromosome 17 and consists of 128 V? and 3 J?. Rearranged IgH, Ig?, and Ig? sequences were obtained from sheep spleen using 5’ RACE PCR. Following PE300 high-throughput sequencing, we analyzed the diversity of V, D, J expression diversity, V(D)J recombination, junctional diversity, and somatic hypermutation in the rearranged sequences. For IgH rearrangement, 4 VH, 4 DH, and 2 JH gene segments were utilized, generating 26 distinct rearrangement types. Ig? rearrangement employed 5 V? and 3 J? gene segments, resulting in 13 rearrangement types. Ig? rearrangement involved 26 V? and 2 J? gene segments, producing 28 rearrangement types. Average length of sheep CDR3H is 44 bp (maximum 66 bp), CDR3? averages 27 bp (maximum 48 bp), and CDR3? averages 30 bp (maximum 47 bp). N-nucleotide additions contributed more significantly to CDR3 diversity than P-nucleotides in both Ig? and Ig? rearrangements. Simultaneously, 3’ V-deletion and 5’ J-deletion further enriched CDR3 diversity. SHM, especially the hotspot mutation motifs, enriches the diversity caused by the V gene segments. Thus, sheep enrich immunoglobulin diversity through both junctional diversity-driven CDR3 diversification and high-intensity SHM. This study expands our understanding of the sheep immunoglobulin gene loci and their expression diversity, providing theoretical foundation for research on immunoglobulin gene evolution within the Bovidae family.
Introduction:
The immune system constitutes a vital defense mechanism through which multicellular organisms recognize and eliminate pathogenic antigens to maintain homeostasis. This complex biological system is functionally divided into two principal components: the innate (non-specific) immune system and the adaptive (specific) immune system ( 1 ). The innate immune system serves as the first-line defense in vertebrates, providing rapid non-specific responses through multiple protective mechanisms. These include mechanical…
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