-Overview -Differentiation -Gene Regulation -Lambda Phage -Muscle

Yarden Yanovich Group 11

The possible fates of a cell:

Remains in the resting state (quiescence, G0 phase)

Proliferation

Differentiation

- is a developmental program when a cell becomes more

specialized both in its morphology and its function.

is a process when stem cells become differentiated tissue

cells. The lack of differentiation is an important feature of

cancer cells!!

Differentiated cells lose the ability to proliferate

Cell senescence: the cell loses its ability to divide after a

certain number of divisions (50 in the case of human cells).

Cell death. It can be passive (necrosis) or active

(apoptosis). In the latter the cell plays an active role.

In vitro differentiation

Differentiation is achieved by regulation by transcription factors and repressors. Lambda bacteriophage

The life cycle of lambda phages is controlled by cI and Cro proteins. The l phage will remain in the lysogenic state if cI proteins predominate, but will be transformed into the lytic cycle if Cro proteins predominate. Transcription of the two proteins is regulated by the cI protein (lambda repressor) itself.

(a) In the absence of cI proteins, the cro gene may be transcribed. (b) In the presence of cI proteins, only the cI gene may be transcribed. (c) At high concentration of cI, transcriptions of both genes are repressed.

Protein A is a transcription regulator that activates its own transcription. All of the descendants of the original cell will therefore “remember” that the progenitor cell had experienced a transient signal that initiated the production of the protein.

A positive feedback loop can create cell memory

the earlier expression pattern is propagated.

Daughter cell of a (partly) differentiated cell

Interference RNA, transcribed from the Xist gene, is important in inhibiting transcription of the inactive X chromosome.

Xist=X-inactive specific transcript

RNA-mediated heterochromatinization

the earlier expression pattern is propagated.

the earlier expression pattern is propagated.

1. generation of myoblast: determination toward muscle differentiation 2. proliferation and migration of myoblasts 3. generation of mature muscle: fusion of myoblasts with each other

new expression pattern

Muscle differentiation:

The daughter cell differentiates further by establishing a new gene expression pattern. Usually achieved by combinative regulation: one transcription factor regulates many genes: only this factor is missing to „fire” these promoters, e.g. MyoD heterodimer

#MyoD - myogenic determination gene D - structure: DNA-binding + dimer formation + activation domain.