Figure 11.

Summary models of transcriptional bursting during lens fiber cell differentiation. Lens fiber cell differentiation is divided into three phases, including “early,” “advanced,” and “late” stages, that correspond to regions a, b, and c/d, respectively. The x axis represents time, and the y axis represents transcriptional status “on” and “off.” Each bar represents one transcriptional burst event. Each crystallin gene studied, Cryaa, Crybb1, and Cryga, employs both bursting parameters, although transcriptional fraction prevails over the transcriptional burst size. In the early lens fibers, transcriptional burst fraction of these crystallins follows the Cryaa > Crybb1 > Cryga pattern. In the advanced lens fibers, transcriptional fraction increases significantly for each of these genes, whereas transcriptional size increases only moderately. In the late lens fibers, expression of Cryaa is attenuated; expression of Crybb1 is moderately attenuated, and expression of Cryga is maintained at “maximal” levels despite the ongoing nuclear condensation, transfer out of nuclear proteins, and denucleation.