Evidence for sequential replacement of gap junctions in chick lens development

Abstract

Freeze fracture analysis of differentiating (elongating) primary and secondary chick lens fiber cells revealed two morphologically distinct populations of gap junctions. Primary and secondary fiber cells in initial stages of elongation were joined by infrequent, small gap junctions which were characterized by the crystalline order of their intramembrane particles (connexons). Stages of rapid elongation of primary and secondary fiber cells were characterized by the development of non-crystalline type junctions and the progressive loss of the crystalline type junctions. Occasionally, crystalline, non-crystalline, developing non-crystalline and mixed crystalline/non-crystalline gap junctions were observed to occur on the same fiber cell at these stages. Fully differentiated (elongated) primary and secondary fiber cells displayed only the non-crystalline type junctions identical to those previously observed in adult, mature secondary lens fiber cells. The results suggest that the crystalline gap junctions may be related to the differentiation of fiber cells, while the non-crystalline gap junctions may be the expression of the differentiated state. allowing intercellular communication between the progressively metabolically incompetent lens fiber cells.