On the mechanism of organelle degradation in the vertebrate lens

Abstract

The programmed elimination of cytoplasmic organelles occurs during terminal differentiation of erythrocytes, keratinocytes and lens fiber cells. In each case, the process is relatively well understood phenomenologically, but the underlying molecular mechanisms have been surprisingly slow to emerge. This brief review considers the particular case of the lens where, in addition to their specialized physiological roles, organelles represent potential sources of light scattering. The article describes how the elimination of organelles from lens cells located on the visual axis contributes to the transparency of lens tissue. Classic anatomical studies of lens organelle degradation are discussed, along with more contemporary work utilizing confocal microscopy and other imaging modalities. Finally, recent data on the biochemistry of organelle degradation are reviewed. Several review articles on lens organelle degradation are available [Wride, M.A., 1996. Cellular and molecular features of lens differentiation: a review of recent advances. Differentiation 61, 77-93; Wride, M.A., 2000. Minireview: apoptosis as seen through a lens. Apoptosis 5, 203-209; Bassnett, S., 2002. Lens organelle degradation. Exp. Eye Res. 74, 1-6; Dahm, R., 2004. Dying to see. Sci. Am. 291, 82-89] and readers are directed to these for a comprehensive discussion of the earlier literature on this topic.

Figure 1

Organelle degradation in differentiating lens fiber cells.