Ontogeny and localization of the crystallins during embryonic lens development in Xenopus laevis

The time of appearance and histological localization of the crystallins, especially the lens‐fiber specific γ crystallins, in the normally developing lens of Xenopus laevis were determined by immunofluorescence techniques. Antibodies to total soluble lens proteins as well as to purified γ crystallins were applied to sections through the eye region of X. laevis embryos, Nieuwkoop‐Faber Stages 23–45. Seven stages of lens development, the earliest highly atypical, were recognized in this species. The first positive immunofluorescence reaction for both the anti‐total and anti‐γ crystallin antibodies occurred at Lens Developmental Stage 3. At this time the lens rudiment is irregular and flattened, with a slightly‐condensed central mass of cells. These centrally located cells, probably prospective primary lens fiber cells, are positive for γ crystallins, while both they and surrounding retinally‐oriented lens cells are positive for total lens crystallins. This general immunofluorescence profile continues during lens development, with only the lens fiber areas positive for γ crystallins. No reaction with either antibody type, however, could be detected in the corneally‐oriented external layer or, later, the lens epithelium, until very late in the development of the lens (Nieuwkoop‐Faber Stage 45). The lack of crystallins in this cell type, together with the transitory appearance of a lens vesicle (lens cavity), delayed until after fiber cells have been formed, sets X. laevis morphological and biochemical lens development apart from that of other vertebrates.