Kangayam and Tharparkar cattle exhibit higher duplications in innate immune genes compared to Sahiwal, Gir, Karan Fries, and Holstein Friesian: insights from an array comparative genomic hybridization.

Abstract

Innate immunity, the primary defence mechanism, encompasses a range of protective processes like anatomical barriers, cytokine secretion, and the action of various immune cells. Cattle breeds might differ in these processes because of their genetic differences such as copy number variations (CNVs). Therefore, the present investigation employed an array comparative genomic hybridisation (aCGH) approach on breed representative pooled DNA samples to evaluate CNVs across six cattle breeds: four indigenous Indian breeds, Kangayam (KNG), Tharparkar (TP), Sahiwal (SW), Gir (GIR), one crossbred Karan Fries (KF), and one exotic breed, Holstein Friesian (HF). In aCGH, HF DNA was used as control, while test DNA was from the other breeds. Each pooled test DNA sample was a representative of 18 animals belonging to three distinct geographical locations of India. The study using Aberration Detection Method 2 (ADM-2) of Agilent Genomic Workbench revealed the highest number of duplications in KNG (1189 genes), followed by TP (534 genes), and the greatest number of deletions in SW (774 genes). Among these genes, 183 and 76 innate immune genes with hub genes TGF-β1, CD79A, and IL4 showed duplications in KNG and TP, respectively. In SW, 113 innate immune genes with hub genes PSMC5, MAPK1, and AXIN1 showed deletions. In contrast, KF and HF showed no genes with deletions and fewer duplicated innate immunity genes, reflecting either lower genetic variability in their immune gene repertoire or a potential bias due to HF DNA as a control in aCGH. Functional enrichment of innate immune genes revealed duplications in KNG enriched in interleukin-1 receptor (IL1R) activity (p = 9.9 × 10^-3) and nucleobase metabolism (p = 2.88 × 10⁻¹¹), while duplications in TP were linked to DNA-binding transcription factor activity (p = 2.34 × 10⁻¹⁴). The KEGG pathway analysis highlighted Th17 cell differentiation (p = 1.3 × 10⁻⁴) in KNG and Hippo signalling (p = 3.7 × 10^-2) in TP. Overall, these findings highlight the importance of genetic diversity in shaping innate immunity in indigenous Indian cattle breeds, favouring a balanced crossbreeding to sustain the Indian dairy sector.