Igk, the immunoglobulin kappa locus, is crucial in developing B cells as it undergoes V(D)J recombination to assemble exons encoding the variable regions of Igκ light chains. This process is essential for the generation of diverse antibodies, enabling the immune system to recognize and respond to a wide array of antigens [1,2,3,6].

Research has shown that Igk has distinct Vκ-to-Jκ joining mechanisms compared to Igh. Igk evolved strong recombination signal sequences (RSSs) to mediate diffusional Vκ-to-Jκ joining. Loop extrusion brings Vκ segments near the Cer element for short-range diffusion-mediated capture by the recombination centre-based RAG [1]. In addition, in pre-B cells, chromatin looping and VK-JK recombination at the Igk locus were insensitive to Wapl upregulation, with the locus having multiple internal loops facilitating VK-JK recombination [3]. Also, Nemo-dependent, ATM-mediated signals from RAG DNA breaks at Igk feedback inhibit Vκ recombination to enforce Igκ allelic exclusion [4].

In summary, Igk is vital for antibody diversity through its unique V(D)J recombination processes. Studies using genetic models have revealed its role in B-cell development, allelic exclusion, and provided insights into how disruptions in these processes might contribute to immunological disorders and malignancies, such as acute myeloid leukemia where IGK expression promotes leukemic cell migration [5].

References:

1. Zhang, Yiwen, Li, Xiang, Ba, Zhaoqing, Alt, Frederick W, Hu, Hongli. 2024. Molecular basis for differential Igk versus Igh V(D)J joining mechanisms. In Nature, 630, 189-197. doi:10.1038/s41586-024-07477-y. https://pubmed.ncbi.nlm.nih.gov/38811728/

2. Langerak, Anton W, van Dongen, Jacques J M. . Recombination in the human IGK locus. In Critical reviews in immunology, 26, 23-42. doi:. https://pubmed.ncbi.nlm.nih.gov/16472067/

3. Hill, Louisa, Wutz, Gordana, Jaritz, Markus, Goloborodko, Anton, Busslinger, Meinrad. 2023. Igh and Igk loci use different folding principles for V gene recombination due to distinct chromosomal architectures of pro-B and pre-B cells. In Nature communications, 14, 2316. doi:10.1038/s41467-023-37994-9. https://pubmed.ncbi.nlm.nih.gov/37085514/

4. Glynn, Rebecca A, Bassing, Craig H. 2021. Nemo-Dependent, ATM-Mediated Signals from RAG DNA Breaks at Igk Feedback Inhibit V κ Recombination to Enforce Igκ Allelic Exclusion. In Journal of immunology (Baltimore, Md. : 1950), 208, 371-383. doi:10.4049/jimmunol.2100696. https://pubmed.ncbi.nlm.nih.gov/34965965/

5. Wang, Chong, Xia, Miaoran, Sun, Xiaoping, Qiu, Xiaoyan, Yin, C Cameron. . IGK with conserved IGΚV/IGΚJ repertoire is expressed in acute myeloid leukemia and promotes leukemic cell migration. In Oncotarget, 6, 39062-72. doi:10.18632/oncotarget.5393. https://pubmed.ncbi.nlm.nih.gov/26429876/

6. Mandal, Malay, Okoreeh, Michael K, Kennedy, Domenick E, Gounari, Fotini, Clark, Marcus R. 2019. CXCR4 signaling directs Igk recombination and the molecular mechanisms of late B lymphopoiesis. In Nature immunology, 20, 1393-1403. doi:10.1038/s41590-019-0468-0. https://pubmed.ncbi.nlm.nih.gov/31477919/