DEVELOPMENTAL PATTERNS OF CRYSTALLIN EXPRESSION DURING LENS FIBER DIFFERENTIATION IN AMPHIBIANS

Data on activation of crystallin synthesis during lens fiber (LF) form ation in amphibians are summarized to point out the questions particul arly interesting in the context of lens cell lineage-specific expressi on programming under different developmental conditions. LFs are known to differentiate throughout life along the same pathway that includes at least five compartments. Using the amphibian eye lens as a model, we have studied how crystallins are expressed in the course of: (1) em bryonic LF formation, (2) LF differentiation in adults, and (3) LF tra nsdifferentiation from other (non-lens) eye tissues. Our experiments s howed that synthesis of crystallins during morphologically similar LF differentiation in embryonic and adult amphibian lens has different sp atial-temporal patterns (i.e., is apparently activated according to di fferent programs). Certain results obtained in our studies suggest the absence of any direct relationship between the capacity of adult newt iris cells to transdifferentiate into LFs and crystallin synthesis (< <molecular predisposition>> to such transdifferentiation) in them. Cry stallins appear at the advanced stages of iris transdifferentiation in to the lens and dynamics of their synthesis in the <<regenerating>> le ns resembles that in the embryonic lens, although a new lens rudiment develops from the adult iris epithelium. Data on alternative patterns of the crystallin gene activation are summarized and compared with rec ent observations on spatial-temporal expression of Pax genes, which pl ay an essential role in lens cell commitment and crystallin synthesis. On this basis, it is suggested that ontogenetic and tissue-or cell-sp ecific changes in Pax gene expression may result in altered programs f or activation of crystallin genes in embryonic, adult, and regeneratin g lens.