Stem Cells and Regeneration

Introduction to Stem Cell Regeneration

Stem cells play a crucial role in regenerating damaged tissues.
Humans can regenerate some body parts like the liver, but regeneration capabilities are limited.
Other animals, like some lizards and salamanders, can regenerate lost tails or limbs.
The planarian is noted for its exceptional regenerative abilities.

Planarians are free-living flatworms found worldwide in wet environments.
They possess a centralized nervous system with two lobes connected to ventral nerve cords.
They have a unique feeding system with a muscular pharynx serving dual functions for ingestion and egestion.
Planarians have photoreceptors (eye spots) that detect light, and they are phototactically negative.
Nearly all planarian cells can act like stem cells, allowing them to regenerate from small fragments.
Planarians can be cut into multiple pieces, each capable of regenerating a whole new organism.

Thomas Hunt Morgan and Charles Darwin studied planarians' regenerative abilities.
Modern studies, like those at the University of Utah's Sanchez Alvarado Lab, focus on understanding the molecular biology of planarian regeneration.
Research uses Schmittia mediterranea to study stem cell biology.

RNA interference (RNAi) is used to identify genes involved in planarian regeneration.
240 genes identified, including a gene coding for the protein Smedwi, similar to the peewee gene in fruit flies.
Peewee gene is important in maintaining stem cells; RNAi experiments mimic radiation effects by eliminating dividing cells.
Discoveries show that Smedwi affects not only stem cell maintenance but also the differentiation of daughter cells.

Identifying and understanding genes involved in planarian regeneration can inform human biology.
Potential future applications could involve pharmacological activation of similar genes in humans.
Multicellularity and stem cells have evolutionary significance, and studying simpler organisms like planarians may reveal insights into human biology.