Adell et al 2010 gradients in planarian regeneration

Question 1

what are planarians?

Answer 1

Platyhelminths that are unsegmented, acoelomate, and possess well defined anteroposterior and dorsoventral axes

Question 2

Planarian regeneration requires the production of new tissue from what?

Answer 2

the unique proliferative and pluripotent stem cells known as neoblasts

HANDBERG-THORSAGER ET AL 2008

Question 3

What happens after amputation to a planarian?

Answer 3

neoblasts close to the wound proliferate, giving rise to the regenerative blastema, defined as the unpigmented tissues where the missing tissues will differentiate

Question 4

what was the process of regeneration in the wound region from proliferating neoblasts termed?

Answer 4

epimorphosis

Question 5

a repatterning of the whole organism is required to recover a complete and proportionate regenerated planarian, this process of remodeling old tissues was termed?

Answer 5

morphallaxis

Question 6

what led to the first hypothesis about a role of morphogenetic gradients?

Answer 6

based on the observation of a differential regenerative capacity along the AP axis

Question 7

what was one of the first issues to be analysed in planarian regeneration was?

Answer 7

how axial polarity is re-established ie how the anterior end makes a head and posterior a tail

Question 8

How is it thought that axial polarity is regenerated?

Answer 8

morphogenetic gradients controlling developing patterns

the positional theory of Lewis Wolpert (1969) as well as the hypothesis of an organising center as the source for a morphogen to which competent cells would respond in discrete thresholds have been theoretical models that have agreed with biological observations

Question 9

what has recently been suggested about axial polarity?

Answer 9

a gradient of neoblast mitotic activity along the AP axis of intact planarians

OVEIDO & LEVIN 2007

Question 10

Which signalling pathways have recently been implicated in the establishment and maintenance of planarian axial polarity?

Answer 10

secreted molecules such as bone morphogenetic protein (BMP) and Wnts

Question 11

what does the wnt / beta catenin signalling pathway do during embryonic development?

Answer 11

evolutionary conserved mechanism that confers polarity

Question 12

what does the wnt / beta catenin signalling pathway control in adult organisms?

Answer 12

controls cell fate and regulates tissue homeostasis through stem cell proliferation and differentiation in adult organisms

REYA & CLEVERS 2005

Question 13

How does the Wnt / beta catenin signalling pathway work?

Answer 13

the binding of wnts to the receptors frizzled and co-receptors LRP leads to the disruption of the beta catenin “degradation complex”

beta cantenin accumulates in the cytoplasm enters the nucleus and activates TCF (transcription factors) that regulate the expression of multiple genes

Question 14

Example of a Wnt that acts as a morphogen?

Answer 14

wingless (Wg) from Drosophila

STRIGINI & COHEN 2000

Question 15

what demonstrates the Wnt / beta catenin signalling pathway in planarians is important in cell fate determination and axial polarity?

Answer 15

IGLESIAS ET AL 2008
2 beta catenins

the silencing of one of them, Smed-beta catenin 1, leads to an extreme phenotype : radial like hypercephalised

Question 16

The severity of the radial like hypercephalized depends on what?

Answer 16

time of regeneration

level of Smed beta catenin 1 inhibition as demonstrated after injection of varying amounts of dsRNA

Question 17

what can explain the different phenotypes observed after the different doses of Smed beta catenin 1 dsRNA injection?

Answer 17

a classical model of morphogenetic gradient activity originated by a posterior organiser

Question 18

Provide evidence for the model of morphogenetic gradient activity

Answer 18

1 - wild type planarians have a gradient of