Stephen L. Johnson, Ph.D.

DEPARTMENT OF Genetics
Keywords: stem cells, cancer, developmental checkpoint, cell proliferation, regeneration

My lab is interested in how animals grow, maintain, and regenerate their form, or the diseases consequent to abnormal growth control such as cancer. We use the freshwater zebrafish as a genetic model system to study growth control mechanisms. Our work concentrates on the biology of stem cells of melanocytes and neural crest, control of organ size, and tissue regeneration. We use mutational, genomic and microarray analysis to understand how these different growth control systems work.

Melanocyte stem cells. The melanocyte pigment pattern is actively surveyed by stem cells in order to replace damaged or amputated portions. We are screening for mutations that are defective for regulation, to identify mechanisms involved in establishing stem cell populations in the embryo, maintaining them through development, or recruiting stem cells when new melanocytes are needed.

Proportionate growth. Zebrafish grow throughout their lives, and maintain proportionality of body parts, including fins, throughout growth. Fins grow by episodic addition of new fin ray segments, and growth control is achieved by regulating entry into new fin ray segment growth cycles. We study fin overgrowth and undergrowth mutants to understand mechansims that control entry into the fin ray segment growth cycle. This will reveal how growth of entire tissues is coordinated and regulated.

Regeneration. In zebrafish, fins regenerate rapidly following amputation to precisely replace amputated portions. We are interested in how cells know to enter regeneration pathway after amputation, how they dedifferentiate, enter a blastema, and decide to grow until the regenerate is complete, then stop growing.