Genetically encoded affinity reagents are a toolkit for visualizing and manipulating endogenous protein function in vivo.

Probing endogenous protein localization and function in vivo remains challenging due to laborious gene targeting and monofunctional alleles. Here, we develop a multifunctional and adaptable toolkit based on genetically encoded affinity reagents (GEARs). GEARs use small epitopes recognized by nanobodies and single chain variable fragments to enable fluorescent visualization, manipulation and degradation of protein targets in vivo. Furthermore, we outline a CRISPR/Cas9-based epitope tagging pipeline to demonstrate its utility for producing knock-in alleles that have broad applications. We use GEARs to examine the native behavior of the pioneer transcription factor Nanog and the planar cell polarity protein Vangl2 during early zebrafish development. Together, this toolkit provides a versatile system for probing and perturbing endogenous protein function while circumventing challenges associated with conventional gene targeting and is broadly available to the model organism community.