Functional expression and localisation of HOPS/TMUB1 in mouse lens

Abstract

Transparency represents the functional phenotype of eye lens. A number of defined steps including quiescence, proliferation, migration and cell differentiation culminates in cell elongation and organelle degradation, allowing the light to reach the retina. HOPS/TMUB1 is a nucleo-cytoplasmic shuttling protein, highly expressed both in vivo and in vitro proliferating systems, bearing an ubiquitin-like domain. The present study shows HOPS expression during the phases of lens cell proliferation and fiber differentiation, and its localization in lens compartments. In lens, HOPS localizes mainly in the nucleus of central epithelial cells. During mitosis HOPS/TMUB1 shuttles to the cytoplasm and returns in the nucleus at the end of mitosis. The differentiating cells share distinct HOPS/TMUB1 localization in transitional zone depending on the differentiation phases. HOPS/TMUB1 is observed in lens cortex and nucleus. Here, it is attached to fibers, having a structural function with crystallin proteins, probably acting in the ubiquitin-proteasome system.