CTNNBL1 (catenin beta like 1) is a component of the PRP19-CDC5L spliceosomal complex essential for pre-mRNA splicing activation 1. The protein functions as a dimer that forms a heterotetramer with CDC5L, with the N-terminal region and ARM repeats critical for oligomerization 1. Beyond splicing, CTNNBL1 participates in AID/AICDA-mediated somatic hypermutation (SHM) and class-switch recombination (CSR) by binding activation-induced cytidine deaminase (AID) and facilitating its nuclear localization 2. Disease-associated CTNNBL1 mutations impair this function; the M466V variant reduces AID-nucleus association, resulting in decreased SHM frequency in immunodeficiency patients 2. CTNNBL1 also restricts HIV-1 replication by suppressing viral DNA integration through interaction with viral integrase 3. In cancer biology, CTNNBL1 is upregulated in high-grade serous ovarian carcinoma where it promotes cell proliferation and invasion while regulating splicing of cancer-related genes like IFI16 and FOXM1 4. Functionally, CTNNBL1 contains nuclear localization signals and localizes to the nucleus, where transient expression induces apoptosis 5. Genetic variants associate with body weight and obesity risk in meta-analyses 6. CTNNBL1 is also linked to episodic memory performance through genotype-dependent effects on brain activation 7.