Atxn1l, an Ataxin-family protein, is known to interact with Capicua (CIC) in both developmental and disease contexts. Together, they form a transcription repressor complex, regulating the repression of CIC target genes, and ATXN1L also promotes the post-translational stability of CIC [1,3]. This complex is involved in multiple biological pathways, such as the MAPK signaling cascade, and is important for normal cellular function and development.

In B cell-specific Atxn1l-deficient (Atxn1lf/f;Cd19-Cre) mice, Notch signaling is disrupted in marginal zone B (MZB) cells. ETV4 de-repression leads to inhibition of Notch1 and Notch2 transcription, inhibiting MZB cell development. Also, in these mice, humoral immune responses and lipopolysaccharide-induced sepsis progression are attenuated but restored upon Etv4-deletion, highlighting the importance of the CIC-ATXN1L complex in MZB cell development and sepsis [2]. In another study, in ATXN1LKO human cell lines, loss of ATXN1L leads to the accumulation of polyubiquitinated CIC protein, promoting its degradation through the proteasome, mediated by the E3 ubiquitin ligase TRIM25 [3].

In conclusion, Atxn1l plays a crucial role in regulating gene expression through its interaction with CIC. Mouse models with Atxn1l deficiency have revealed its significance in B cell development and sepsis progression. The study of Atxn1l using these genetic models helps to understand the complex regulatory mechanisms in normal biological processes and disease conditions, especially in relation to immune-related diseases.