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 Student’s name: Kattie Sepehri

Topic chosen: Planarian regeneration

 

SPECIFIC QUESTION: How is loss of eye spots signalled to the neoblasts to produce optic cup progenitors?

 

 

HYPOTHESIS:A long distance signalling mechanism involving changes in concentration gradient of a morphogen(s), that is produced specifically by the eye spots, is responsible in inhibiting the production of optic cup progenitors by the neoblasts closest to the eye spots.

 

 

EVIDENCE ON WHICH THE HYPOTHESIS IS BASED (INCLUDE REFERENCES):

• S., Reddien. P. dlxand sp6-9 Control Optic Cup Regeneration in a Prototypic Eye, PLOS. 2011;7.
• Identified two genes that make TFs, expressed specifically in the optic cup.
• RNAi of these genes prevented the formation of optic cups
• Optic cup formation occurred after migration of progressively differentiated progenitor cells from the neoblasts.
• Suggests that there might be a long distance signaling mechanism

 

• H., Browne. A. Inhibition of regeneration in planarians by grafting: technique of grafting. PNAS. 1926; 12:9.
• Graft a head excised just behind the eyes of one animal onto the side of the anterior portion of the body of another, remove the original head, the regeneration of a new head seems to become inhibited and the grafted head swung into the body axis.

 

• K., Hashiguchi. T., Ichikawa. T., Ishino. Y., Hoshi. M., Matsumoto., M. Neoblast-enriched fraction rescues eye formation in eye-defective planarian ‘menashi’ Dugesia ryukyuensis. Development, Growth & Differentiation. 2008; 50 (8).
• An eye defective mutant, mensashi, was able to regenerate eye pigment cells after irradiation and transplantation of neoblast-rich fraction.
• May suggest a lack of an inhibitory signalling mechanism that is not present in the mensashi mutants due to having no eye spots.

·         Wenemoser. D., Reddien. P. Planarian regeneration involves distinct stem cell responses to wounds and tissue absence. Elsevier. 2010; 344:2.

o   Suggests that injury leads to two miotic peaks in the body. The  first mitotic peak is a body-wide response to any injury and the second mitotic peak is a localized neoblast response when the injury causes loss of tissue. This second response causes the recruitment of neoblasts to the wound site. Therefore it is possible that the key determinant to the second mitotic peak is the absence of tissue.

o   The neoblast accumulation and migration around the wound site suggests that regeneration initiation may involve a signal from injuries.

 

 

 

PREDICTION(S):

 

• The regeneration rate of the eye spots will change/stay the same when more eye spots are removed or displaced due to a possible inhibitory signal that is produced by the eyes that stops the formation of progenitors by the neoblasts.

 

 

EXPERIMENTAL APPROACH TO TEST PREDICTION (INCLUDE ANY DETAILS THAT YOU HAVE WORKED OUT SO FAR):

 

First approach: To test the possibility of a signal and a concentration gradient produced by the eye spots, we will surgically remove the eyespots and at the same time we will transplant eye spots into a different location. If eye spots have a specific signal to show their presence and this signal is responsible in inducing the optic cup progenitors, then the planarian with transplanted eye spot should have a slower eye regeneration rate.

 

Second approach: Another method to test the presence of a signal is to remove ectopic eye spots from mutant planarians with more than 2 eyes, these mutants should have slower eye regeneration than wild type planarians as there will be a smaller change in signal.

 

Third approach: Transplant eye regions from a defective mutant planarian ‘menashi’ (unable to form functional black eye spots but forms white spots that contain most of the eye cells) into a wild type planarian that has its eye spots removed. If an inhibitory long distance signal is produced by these cells then the planarian should not regenerate new eye spots.

 

 

 

 

 

 

LIST OF RELEVANT PRIMARY AND REVIEW ARTICLES READ, AND SUMMARY OF RELEVANT INFORMATION FROM EACH (this is the start of an annotated bibliography):

 

• F. Studies on transplantation in planaria. Biological Bulletin. 1929; 57:188-197.
• Transplanting different areas of the planarian, including the areas around the eyes

 

• Guedelhoefer IV. O., Alvarado. A. Planarian Immobilization, Partial Irradiation, and Tissue Transplantation. J Vis Exp. 2012; 66: 405.
• Detailed protocols for tissue transplantation

 

• C., Saito. Y., Ogawa. K., Agata. K.Wnt signaling is required for antero-posterior patterning of the planarian brain. Elsevier. 2007; 306:2.
• The mutants created in this study have more than 2 eye spots and can be used in my experiment.

 

·         Cebria. F., Newmark . P. Morphogenesis defects are associated with abnormal nervous system regeneration following roboA RNAi in planarians. Development. 2007; 134.

o   Role of nervous system in regulating morphogenesis during the regeneration of the anterior part of planarian. Smed-roboA is important in guidance of visual axons, and the RNAi mutants of this gene have ectopic projections and visual defects. In the case of my question this could suggest that the long distance signal is carried by the nervous system.

• R., Newmark. P. The cell biology of regeneration. The Journal of Cell Biology. 2012; 196: 5.
• Discussion of regeneration in other organisms such and also planarians. Evidence suggests conservation of regenerative abilities through evolution.

 

·         Adell. T., Cebria. F., Salo. E. Gradients in Planarian Regeneration and Homeostasis. CSH Perspectives. 2012; 2:1.

o   Discusses the gradients that are involved in planarian regeneration and polarity, such as BMP, Wnt and FGF. These gradients could also be important in my experiment and should be taken into consideration.

• Newmark, P., Alvarado. A. Regeneration in Planaria. Nature Publishing Group. 2001.
• Contains an introduction to regeneration in planarian and some histroy of research in this field. Also a proposed mechanism in regeneration such as the role of neoblasts is discussed.

 

 

 

HOW DOES THE QUESTION FIT INTO THE BROADER PICTURE, AND WHAT IS ITS IMPACT?

 

• This question fits into the broader picture of developing a model for planarian regeneration. This model is important because it gives us insight into the process of regeneration and stem cells.
• This question can give us the opportunity to address problems in development and stem cell differentiation.
• Another potential impact of this question is gaining a deeper understanding of injury and wound signalling that could also apply to humans.
• There seems to be a parallel between planarian stem cells and the stem cells in mammals.

 

 

 

POTENTIAL WAYS TO MAKE YOUR QUESTION KNOWN TO THE PUBLIC AT LARGE (OR TO YOUR NON-BIOLOGIST FAMILY AND FRIENDS):

• The findings for this question can be used in stem cell research and health care. Also the concept of planarian regeneration is very easy to demonstrate without having a significant knowledge about biology.
• Demonstrations of the cool regenerative powers of planarians can easily be shown by cutting them into tinny pieces and letting them form a new organism.  This demonstration could raise the curiosity of the public about this complex process.

 

 

ANY OTHER PARTS OF THE PROJECT COMPLETED SO FAR:

 

 

ANYTHING YOU WOULD LIKE SPECIFIC FEEDBACK ON:

• The experimental procedure, since I have doubts about whether it is possible to transplant an eye spot – cannot find any research that successfully transplanted an eye spot into another part of the body, but there is some research/techniques on transplantation of the eye spots and the tissue around it. Therefore my 1st and 3rd approaches  could lead to failure if the transplanted eyes spots are simply reabsorbed….
• Ways to make my question known to the public…