Variant-specific functional effects of CTNNA1 in a humanized Drosophila model.

Germline variants in CTNNA1, encoding αE-catenin, have been implicated in hereditary diffuse gastric cancer (HDGC) and macular dystrophy patterned-2 (MDPT2). However, the functional mechanisms associated specifically with each molecular variant type underlying these distinct clinical outcomes remain poorly understood. Here, we established a humanized Drosophila melanogaster model conditionally targeting two distinct Drosophila tissues: the eye and the wing. We assessed the functional impact of eight CTNNA1 variants identified in 50 carrier families. We used tissue-specific RNAi and CRISPR/Cas9 to deplete endogenous Drosophila α-catenin (Dα-cat) and expressed either human wild-type (WT) or mutant αE-catenin (Hα-cat). We demonstrate that WT Hα-cat rescued Dα-cat loss, supporting conserved functionality across species. Hα-cat truncating variants failed to rescue epithelial architecture or viability and were associated with increased apoptosis, although one nonsense variant located in the CTNNA1 last exon exhibited milder phenotypes. Interestingly, while most missense variants behaved similarly to WT, p. Asn853Ser, in CTNNA1 last exon, exhibited partial functional loss and did not fully rescue apoptosis caused by Dcat expression loss. These results highlight variant-type and tissue-type specificities. This work provides a humanized Drosophila model for the CTNNA1 gene, which reveals variant-type and locus-specific impacts of CTNNA1 alterations, occurring either in HDGC or MDPT2 families. Our study highlights the value of in vivo functional modeling for clinical variant interpretation and supports improved classification and management strategies for CTNNA1 variant carriers.