Lecture Notes

Morphogens, pattern formation and regeneration in planarians
Planarians

 Animal model




The internal structure of a planaria

 Planarian can be either sexual or asexual reproduction.
 Green = nervous system
 Yellow = digestive system
 Sexually reproducing planarians are hermaphrodites (both partners can act as male
or female)
 Blue = ovaries
 Red = testes
 At a low percentage, self-fertilisation can occur.
 Transverse section (cross section) through asexual planaria

Planarian life cycles

 Regeneration:
- Attach self to surface tightly
- Rip selves apart
- Tear themselves into 2 pieces
- The anterior planarian will grow the posterior and vice versa
- Outcome: 2 planaria




Planarians can shrink in unfavourable environments to save energy, which is called degrowth

, Planarian regeneration under the microscope

 Planarian cut into 3 section
 The middle section (ph = pharynx)
 Blastemal = group of dividing cells capable for growth and regeneration into organs or body parts.
 Blastema formation in the anterior area, which will regenerate the head
 Blastema formation in the posterior area, which will regenerate the tail.
 After 17 days = complete regeneration of planarian




How do the cells now which part to regenerate?

 Planarians have stem cells, which are called neoblasts
 Neoblasts migrate to the wound and bind there, then differentiate to the type of cells needed to form the rest of the body.
 Neoblasts can give rise to all different tissue/cells needed to regenerate planaria
- nervous system tissues
- digestive system tissues
- etc