Functional Analysis of Genes Involved in Regulating Stem Cell Maintenance and Differentiation in the Freshwater Planarian Schmidtea Mediterranea

Freshwater planarians have been a classic model for regeneration studies for more than 250 years. The great regenerative abilities of planarians rely on neoblasts, adult stem cells maintained throughout the animal's life. This thesis reports an analysis of genes that regulate stem cell maintenance and differentiation in planarian Schmidtea mediterranea. A member of the Bruno-like family of RNA binding proteins was found to be critical for neoblast self-renewal in the planarian Schmidtea mediterranea. Smed-bruno-like (bruli) mRNA and protein are expressed in the neoblasts and in the central nervous system. Immunofluorecense with antibodies recognizing SMEDWI-1 and Historie H4 (monomethyl-K20) and other cell cycle markers showed that the neoblast population was eliminated from both regenerating and intact planarians following smed-bruli RNA interference, leading to the death of the animals. These results suggest that Bruli is required for stem cell maintenance. We further characterized expression of SMEDWI-1 in somatic stem cells and germ cells. SMEDWI-1 protein is expressed in neoblasts and their differentiating progeny in both asexual and sexual planarians. In sexual planarians, SMEDWI-1 expression is detected in spermatogonia and spermatocytes as well as oogonia. SMEDWI-1 antibodies also recognize the presumptive germ cells in asexual planarians that reproduce exclusively by fission. However, SMEDWI-1 protein is dispensable for the development, maintenance and regeneration of testes in sexual planarians, probably due to the redundancy of other PIWI family members expressed in germ cells. Finally, we examined the differentiation of neoblasts in intact and Smed-slit RNAi planarians. BraU incorporation and immunofluorescent labeling with cell type-specific markers were used to label proliferating neoblasts and follow the fates of their progeny into various differentiated cell types, including marginal gland cells, photoreceptors, and neurons. In slit RNAi animals, neoblasts differentiate into ectopic neural tissues that form ganglia-like structures along the midline. Thus, Smed-slit may function to regulate neoblast differentiation in addition to acting as a repulsive cue in axon guidance.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Cell and Developmental Biology

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Guo, Tingxia

Contributors dc:contributor

• Joseph Henry

• Biology, Cell

Language dc:language

eng

Identifier

(MiAaPQ)AAI3301142

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/86310