Generation of a Triple Tag Knock-In Mouse to Visualize Precise Protein Localization Patterns for Type II Classic...

Classic cadherin cell-cell adhesion molecules with self-organizing activities play roles in segregating distinct populations of cells at developing brain regions and/or boundaries. However, the protein dynamics of each cadherin subclass in the mouse embryonic brain is poorly described due to the low antigenicity. Here, we generate Cdh6-HA and Cdh8-PA tag knock-in (KI) mice by CRISPR/Cas9-mediated genome editing and establish Cdh6^HA/HA; Cdh8^PA/PA; Cdh11^EGFP/EGFP triple tag KI homo mice with normal viability and fertility. Immunostaining with specific antibodies for these tags reveals differential protein expression profiles almost comparable with mRNA in situ hybridization (ISH) results during embryonic brain development. We can additionally detect considerable levels of immunostaining signals outside the mRNA ISH-positive areas, specifically along the nerve tracts, suggesting physiological accumulation of these type II cadherin proteins along axons. By using super-resolution imaging, we further evaluate cadherin subcellular localization dynamics around the zona limitans intrathalamica to confirm that the prosomere 2/3 compartment boundary at E12.5 is maintained by the distinctive integration of Cdh6 or Cdh11 at apical attachment sites of the ventricular cells. These results highlight the value of the genetic tag KI strategy for proteins with low antigenicity and the functional relevance of type II classic cadherins in brain development.