posted on 2021-10-20, 12:00authored byMiguel Jarrin, Fiona C. Mansergh, Michael E. Boulton, Lena Gunhaga, Michael A. Wride
Purpose: Survivin (Birc5) is the smallest member of the inhibitor of apoptosis (IAP) protein family, which regulates
the cell cycle/apoptosis balance. The purpose of this study was to examine Survivin expression in the embryonic chick
lens, in chick lens epithelial cell cultures, and in the postnatal mouse lens.
Methods: Survivin expression was examined using a combination of quantitative real-time polymerase chain reaction,
western blotting, and immunocytochemistry. To correlate Survivin expression with the timing of proliferation, we
determined the profile of cell proliferation in the developing lens using the cell cycle marker proliferating cell nuclear
antigen (PCNA) in quantitative western blotting and immunocytochemistry studies. We also examined the expression of
PCNA and the extent of denucleation using terminal deoxynucleotidyl transferase (TdT)-mediated biotin-dUTP nick-end
labeling (TUNEL) of lentoids (lens fiber-like cells) during chick lens epithelial cell differentiation in vitro.
Results: At embryonic day (ED) 4, Survivin immunostaining was present in two pools in lens epithelial cells and fiber
cells: cytoplasmic and nuclear. The nuclear staining became more pronounced as the lens epithelial cells differentiated
into lens fiber cells. At ED12, Survivin staining was observed in lens fiber cell nuclei containing marginalized chroma tin, indicative of early denucleation events. Using western blotting, Survivin expression peaked at ED6, diminishing
thereafter. This profile of expression correlated with the events in chick lens epithelial cell cultures: i) increased Survivin
expression was associated with an increase in PCNA staining up to day 6 of culture and ii) downregulation of Survivin
expression at day 8 of culture was coincident with a dramatic decrease in PCNA staining and an increase in TdT-mediated
biotin-dUTP nick-end labeling in lentoids. In early postnatal mouse lenses, Survivin and PCNA were highly expressed
and decreased thereafter during postnatal lens maturation.
Conclusions: Survivin is expressed during chick and mouse lens development and in chick lens epithelial cell cultures.
High levels of Survivin expression correlated with high rates of proliferation of lens epithelial cells at early stages of
development. Downregulation of Survivin expression with development and its progressive localization to the nuclei
of lens fiber cells was coincident with a decrease in cell proliferation and increased denucleation in differentiating lens
fiber cells. These studies suggest an important role for Survivin as a dual regulator of lens epithelial cell proliferation
and lens fiber cell differentiation.