CSB329H1 Lecture Notes - Lecture 3: Planarian, Spermatozoon, Development Of The Gonads
9 May 2018
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Figure 1.0
Lecture 3(a): Flatworms and Roundworm Stem Cells
ð A newly fertilized egg (few first cells) are considered to be totipotent – are capable of
generating an entire organism
o Inner cell mass are pluripotent – can regenerate the entire embryo; however,
mammals have extra embryonic tissue not allowing them to generate a placenta
Stem Cells:
• Properties include the ability to self-renew and the generation if differentiated progeny
• However, gives rise to two difficult issues:
o Self-renewed stem cells must avoid cell cycle arrest and differentiation
o Prevent uncontrolled proliferation and differentiation leading to tumor formation
(i.e. teratoma – major issue in stem cell therapy)
§ Teratoma is a tumor made up of multiple cells 9(i.e. bone, muscle and hair)
Flatworms – Planaria:
• Have pluripotent somatic stem cells (neoblasts)
o If amputated, the neoblasts are capable of regenerating
an entire organism
§ Majority of the flatworms are parasitic (not this)
Question – Why are their somatic stem cells referred to as ‘pluripotent’ and not totipotent?
• Some literature call it totipotent, some call it pluripotent – just the way it is
Planarian Brain Regeneration:
• Planarians can be cut into small pieces and regenerate into a
complete organism
o i.e. a fragment (1/279) of the animal can regenerate
an intact animal via asexual reproduction
(capable of also undergoing sexual reproduction)
ð Anterior-facing wound will function to regenerate a new head
or anterior region
ð Posterior-facing wound will function to generate a new tail
or posterior region
Figure 1.0
• Represents whole mount in-situ hybridization of piwi-1 gene expression
o Illustrates planarian pluripotent neoblastic (
somatic
stem cell)
distribution throughout the body
§ Neoblasts are somatic stem cells, NOT germ cells
ð Blastema is a mass of undifferentiated cells will undergo reprogramming
to generate the missing region of the Planaria; whitish blob epithelia
Document Summary
Teratoma is a tumor made up of multiple cells 9(i. e. bone, muscle and hair) Flatworms planaria: have pluripotent somatic stem cells (neoblasts, if amputated, the neoblasts are capable of regenerating an entire organism. Majority of the flatworms are parasitic (not this) Question why are their somatic stem cells referred to as pluripotent" and not totipotent: some literature call it totipotent, some call it pluripotent just the way it is. Planarian brain regeneration: planarians can be cut into small pieces and regenerate into a complete organism i. e. a fragment (1/279) of the animal can regenerate an intact animal via asexual reproduction (capable of also undergoing sexual reproduction) Anterior-facing wound will function to regenerate a new head or anterior region. Posterior-facing wound will function to generate a new tail or posterior region. Figure 1. 0: represents whole mount in-situ hybridization of piwi-1 gene expression, illustrates planarian pluripotent neoblastic (somatic stem cell) distribution throughout the body. Neoblasts are somatic stem cells, not germ cells.
