The genomes of most vertebrates contain many V, D, and J gene segments within their Ig loci to construct highly variable CDR3 sequences through combinatorial diversity. This nucleotide variability translates into an antibody population containing extensive paratope diversity. Cattle have relatively few functional VDJ gene segments, requiring innovative approaches for generating diversity like the use of ultralong-encoding IGHV and IGHD gene segments that yield dramatically elongated CDR H3. Unique knob and stalk microdomains create protracted paratopes, where the antigen-binding knob sits atop a long stalk, allowing the antibody to bind both surface and recessed antigen epitopes. We examined genomes of twelve species of Bovidae to determine when ultralong-encoding IGHV and IGHD gene segments evolved. We located the 8-bp duplication encoding the unique TTVHQ motif in ultralong IGHV segments in six Bovid species (cattle, zebu, wild yak, domestic yak, American bison, and domestic gayal), but we did not find evidence of the duplication in species beyond the Bos and Bison genera. Additionally, we analyzed mRNA from bison spleen and identified a rich repertoire of expressed ultralong CDR H3 antibody mRNA, suggesting that bison use ultralong IGHV transcripts in their host defense. We found ultralong-encoding IGHD gene segments in all the same species except domestic yak, but again not beyond the Bos and Bison clade. Thus, the duplication event leading to this ultralong-encoding IGHV gene segment and the emergence of the ultralong-encoding IGHD gene segment appears to have evolved in a common ancestor of the Bos and Bison genera 5–10 million years ago.

大多数脊椎动物的基因组在其 Ig 位点内包含许多 V、D 和 J 基因片段，以通过组合多样性构建高度可变的 CDR3 序列。这种核苷酸变异性转化为含有广泛互补位多样性的抗体群体。牛的功能性 VDJ 基因片段相对较少，需要创新方法来产生多样性，例如使用超长编码 IGHV 和 IGHD 基因片段来产生显着延长的 CDR H3。独特的旋钮和柄微结构域创建了延长的互补位，其中抗原结合旋钮位于长柄的顶部，使抗体能够结合表面和凹进的抗原表位。我们检查了 12 种牛科动物的基因组，以确定超长编码 IGHV 和 IGHD 基因片段何时进化。我们在六种牛科动物（牛、瘤牛、野牦牛、家养牦牛、美洲野牛和家养牛）的超长 IGHV 片段中发现了编码独特 TTVHQ 基序的 8 bp 重复，但我们没有发现物种中重复的证据超出了Bos和Bison属。此外，我们分析了野牛脾脏的 mRNA，并鉴定了表达的超长 CDR H3 抗体 mRNA 的丰富库，表明野牛在宿主防御中使用超长 IGHV 转录本。我们在除家养牦牛之外的所有同一物种中都发现了超长编码 IGHD 基因片段，但同样不超出野牛和野牛分支。因此，导致超长编码IGHV基因片段和超长编码IGHD基因片段出现的复制事件似乎是在5-1000万年前在野牛属和野牛属的共同祖先中进化 而来的。