Transdifferentiated embryonic neuroretina cells: an in vitro system to study crystallin aggregation process

Transdifferentiated embryonic quail neuroretina cells synthesize in vitro crystallins (the lens-specific proteins) and form lentoid bodies (structures that mimic lens fiber cells) which also contain crystallins. A comparative study on the size of crystallins is reported in 7-day-old embryonic quail lenses, in 7-day-old embryonic quail transdifferentiated neuroretina cells (normal and MH2 transformed), and in isolated lentoid bodies. Analyses are performed using Superose FPLC in combination with SDS-PAGE and Western blot procedures. In quail lenses, an apparent 560-580-kDa alpha crystallin homopolymer is found and delta crystallin, the major avian lens protein, is detected as a 180-kDa tetramer. beta Crystallins, present in low amount within the 180-kDa peak, are a heterogeneous population composed of subunits of molecular weight identical to those found in chick lenses. In addition, an apparent 46-kDa monomeric delta crystallin is found. Normal and MH2-transformed neuroretina cultures produce an alpha crystallin polymer of lower molecular weight (450 kDa) and delta crystallin in a monomeric or dimeric form. The Western blot pattern of beta crystallins from MH2-transformed neuroretina cultures is strictly identical to that of quail lens beta crystallins. In particular, the beta B1 crystallin, which is specific to lens fiber cell differentiation, and the major beta 25-kDa crystallin are present. However, analysis of isolated lentoid bodies from normal transdifferentiated quail neuroretina cultures showed alpha and delta crystallins of comparable size to those found in lens extract, in particular the delta crystallin in tetrameric form. The lentoid body lens-like structure could favour the crystallin aggregation process.