Figure 1.

Cellular organization of the vertebrate lens. The lens is bounded by the lens capsule (Cap). (a,b) Its anterior surface is covered by a monolayer of epithelial cells (Ep). The primary lens fibre cells (pLF) are formed early in embryonic development and constitute the embryonic nucleus in the adult lens. Secondary lens fibre cells are formed continuously by mitosis of cells in the germinative zone (GZ) at the equatorial margin of the epithelium. The fibres are stacked one upon another in meridional rows (c). These secondary lens fibre cells differentiate (b, dLF) and subsequently elongate (b, eLF) beneath the apical surface of the epithelium (f, aEp) and along the posterior capsule until their tips reach the anterior (aS) and posterior (pS) sutures. Mature fibre cells in the organelle-free zone (OFZ) of the lens lack nuclei and other organelles. Most fibre cells are hexagonal in cross-section and very regularly organized in closed sheets as shown in the light and scanning electron microscope images of (d) and (e). Diagram adapted from Shi et al. [9]. GC, growth cone.