CA2- CELLULAR AND MOLECULAR RESPONSES( SIGNALING IN THE CHLAMYDOMONASFLAGELLAR REGENERATION SYSTEM )

In response to certain extracellular stimuli, Chlamydomonas reinhardti i cells excise their flagella, induce expression of more than 200 diff erent flagellar mRNAs, and assemble a new flagellar pair. Normally, fl agellar excision, gene induction and outgrowth are tightly coupled tem porally. Our previous studies showed that uncoupling the cellular resp onse of flagellar excision from flagellar outgrowth resulted in submax imal flagellar gene induction, and led us to propose that normal flage llar gene induction is a composite response. The present study extends these observations by measuring flagellar gene induction in Chlamydom onas cells stimulated under conditions where both flagellar excision a nd flagellar outgrowth are blocked. We find that the flagellar genes a re induced in a Ca2+-dependent manner in response to stimulation in th e absence of flagellar excision and outgrowth. Flagellar gene inductio n is therefore independent of flagellar excision and outgrowth but sen sitive to extracellular Ca2+ levels. Thus, flagellar excision, flagell ar outgrowth and flagellar gene induction are three responses to a com mon stimulus that are related by their requirement for extracellular C a2+.