BioID2 screening identifies KIAA1671 as an EPS8 proximal factor that marks sites of microvillus growth

摘要

Microvilli are defining morphological features of the apical surfaces in diverse epithelial tissues. To develop our understanding of microvillus biogenesis, we used a biotin proximity-labeling approach to uncover new molecules enriched near EPS8, a well-studied marker of the microvillus distal tip compartment. Mass spectrometry of biotinylated hits iden-tified KIAA1671, a large (similar to 200 kDa), disordered, and previously uncharacterized protein. Based on immunofluorescent staining and expression of fluorescent protein-tagged con-structs, we found that KIAA1671 localizes to the base of the brush border in native intestinal tissue and polarized epithelial-cell culture models, as well as dynamic actin-rich structures in unpolarized, nonepithelial cell types. Live imaging also revealed that during the early stages of microvillar growth, KIAA1671 colocalizes with EPS8 in diffraction-limited puncta. However, once elongation of the core bundle begins, these two factors separate, with EPS8 tracking the distal end and KIAA1671 remaining behind at the base of the structure. These results suggest that KIAA1671 cooperates with EPS8 and potentially other assembly factors to initi-ate growth of microvilli on the apical surface. These findings offer new details on how trans-porting epithelial cells builds the brush border and may inform our understanding of how apical specializations are assembled in other epithelial contexts.