Building the Brush Border, One Microvillus at a Time.

Microvilli are actin bundle-supported surface protrusions assembled by diverse cell types to mediate biochemical and physical interactions with the external environment. Found on the surface of some of the earliest animal cells, primordial microvilli likely contributed to bacterial entrapment and feeding. Although millions of years of evolution have repurposed these protrusions to fulfill diverse roles such as detection of mechanical or visual stimuli in inner ear hair cells or retinal pigmented epithelial cells, respectively, solute uptake remains a key essential function linked to these structures. In this mini review, we offer a brief overview of the composition and structure of epithelial microvilli, highlight recent discoveries on the growth of these protrusions early in differentiation, and point to fundamental questions surrounding microvilli biogenesis that remain open for future studies.