Suzanne Craig

Date of Award

Summer 8-2018

Document Type


Degree Name

Master of Science (MS)



First Advisor

Robert Major, Ph.D.

Second Advisor

Christina Ruby, Ph.D.

Third Advisor

Robert Hinrichsen, Ph.D.


The regeneration capabilities of humans are limited. In contrast, planarians have incredible regeneration capabilities. Recently, planarians have become a popular model system for studying regeneration mechanisms. The remarkable regeneration abilities of planarians are derived from a population of adult stem cells called neoblasts. Previous results from our laboratory revealed that a circadian rhythm gene, called timeless, produces phenotypes associated with neoblast deficiency. The circadian clock has relationships with both the cell cycle and stem cell control, but the role of circadian rhythms and clock genes in regeneration is not understood. We found that targeting timeless for dsRNA interference significantly reduced the amount of mitotic neoblasts in both whole planarians and amputated fragments. This demonstrates a role for timeless in the control of neoblast proliferation. We hypothesize that timeless is a communication link between circadian rhythms and cell cycle control and uses these pathways to control neoblast function during regeneration.