Generation and Characterization of a TRIM21 Overexpressing Mouse Line

ABSTRACT Specific removal of a protein is a key to understanding its function. “Trim‐Away” utilizes TRIM21, an antibody receptor and ubiquitin ligase, for acute and specific reduction of proteins. When TRIM21 is expressed in cells, introduction of a specific antibody causes rapid degradation of the targeted protein; however, TRIM21 is endogenously expressed in few cell types. We have generated a mouse line using CRISPR to insert a conditional overexpression cassette of TRIM21 into the safe harbor site, Rosa26. These conditionally‐expressing mice can be bred to a wide variety of Cre mice to target cell‐specific TRIM21 overexpression in different tissues. Zp3Cre mice expressed TRIM21 protein specifically in oocytes, whereas HprtCre mice expressed the protein globally. When TRIM21‐overexpressing oocytes were microinjected with specific antibodies targeting either the IP3 receptor or SNAP23, these proteins were effectively degraded. In addition, cortical neural cells from globally‐overexpressing TRIM21 mice showed a dramatic reduction in IP3 receptor protein within hours after electroporation of a specific antibody. These experiments confirm the effectiveness of the Trim‐Away method for protein reduction. These mice should make a valuable addition to the broader research community, as a wide range of proteins and cell types can be studied using this method.