Understanding the expression, interactions, and functions of endogenous proteins is crucial for elucidating biological mechanisms and disease pathology. However, studying endogenous proteins presents significant challenges due to the inherent complexity of cellular environments, the low abundance of specific proteins, and transient protein-protein interactions. We are using a systematic approach to generate reporter cell lines using the CRISPR-Cas9 system, which offers a powerful tool to study endogenous proteins and cellular processes with unprecedented spatial and temporal resolution. By taking advantage of these reporter cell lines in human pluripotent cell lines, we aim to address fundamental questions in developmental biology.