Question

1. What happens when you inhibit Wnt signaling in a center piece of a planarian worm (ie it had both its head and tail removed)?

A. Regeneration is inhibited

B. two tails form

C.two heads form

D. a head and tail form

2. Classification of the barnacle as a crustacean based on its larval form is an example of:

A. Adaptation to environmental conditions

B. unity of type
C. both A and B

3.Chronologically order the following stages of limb regeneration

- Differentiation of the blastema cells into the tissues of the regenerate

-Pattern formation in the regenerate

-Establishment of the wound epithelium over the site of injury

-Innervation of the wound epithelium

-Dedifferentiation of the mature limb cells into blastema cells

-Establishment of the AEC signaling center

Answer 1

1. a head and tail form

Most animal species have regenerated tissues lost by injury with various degrees of success and some of these animals display extraordinary regenerative capacities. Wnt signaling is an important and crucial signal in the whole life of animals because it helps the animal to regenerate fro early life to adulthood. In intact and regenerating planarians, the regulation of the Wnt/β-catenin signaling function is to maintain and specify anterior/posterior (A/P) identity. according to one study of the planaria by the group of scientist, they experimented the same inhibiting the center part of the planarian body they found the genes which are found that is for wnt have a complete absence of stem cells, and despite a strong induction of wnt1 at the anterior wound, differentiated cells located at the anterior end of a tail fragment recognize their new relative location and change their gene expression accordingly.and they interpret the combined data from head and tail fragments to reveal that cells throughout the animal are capable of expressing anterior- or posterior-specific genes during regeneration that they would otherwise never express in the intact animal. Moreover, this anterior/posterior plasticity does not require the presence of stem cells.

one study revealed that, Planaria can regenerate any tissue damaged by an injury and the processes of head or tail regeneration serve as simple models for the study of mechanisms that relate wounding to stem cell activation and growth signaling. Planarians have an adult pluripotent stem cells of the neoblast population for producing all differentiated cell types needed for whole-body regeneration and for viability through ongoing tissue homeostasis Neoblasts express the PIWI homolog smedwi-1 and are the only known proliferating cells in planarians, so FACS isolation of G2/S/M cells labeled with DNA-binding vital dyes can purify this cell population. Neoblasts respond to injury through changes in proliferation, localization, and gene expression RNAi and small molecule treatments have implicated several signaling pathways and processes in head and tail regeneration that therefore directly or indirectly control the function of neoblasts or their differentiating progeny, including Wnt signaling

Neoblast-dependent processes were likely to provide input into the control of canonical Wnt signaling that directs head and tail regeneration and polarized responses on the anteroposterior (A/P) axis. By contrast, notum encodes a secreted hydrolase that can inhibit Wnt signaling in planaria and is required for head regeneration in planarians. Injury activates notum expression preferentially at anterior-facing injury sites within body-wall muscle cells with kinetics similar to wound-induced wnt1 expression. Subsequently, by 48–72 hours, in fragments regenerating a new head, notum is expressed in a focus of cells at the newly forming anterior pole. Temporal RNAi experiments found that wnt1 and notum are required during tail and head regeneration.the evolutionarily ancient β-catenin protein acts as a molecular switch in adult planarians and that it may play a similar role in the adult tissues of other animals.

2. unity of type

the development of barnacles are found in the three larval stages at the time at the larval stage it becomes in a very dangerous environment the predator can also eat them for those they can protect by these characteristics.

3. correct sequence is

Differentiation of the blastema cells into the tissues of the regenerate

Establishment of the wound epithelium over the site of injury

Innervation of the wound epithelium

Pattern formation in the regenerate

Dedifferentiation of the mature limb cells into blastema cells

Establishment of the AEC signaling center