recap

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19.2 recap

Cell fate determination involves cytoplasmic segregation and induction. Cytoplasmic segregation is the unequal distribution of gene products in the egg, zygote, or early embryo. Induction occurs when one cell or tissue sends a chemical signal to another. Cell fate determination involves the activation of signal transduction pathways that lead to differential gene expression. Differentiation involves selective gene expression, controlled at the level of transcription by transcription factors.

learning outcomes

You should be able to:

  • Summarize how cytoplasmic segregation results in polarity in a fertilized egg and how this polarity affects cell fate determination.

  • Predict the consequences of manipulations of inducer-producing cells on development and differentiation.

  • Predict cellular, gene-expression, and phenotypic consequences of experimental manipulations of a transcription factor, such as MyoD concentrations on the development of muscle tissue.

Question 1

How does cytoplasmic segregation result in polarity in a fertilized egg, and how does polarity affect cell fate determination?

Unequal distribution of a cytoplasmic component in the fertilized egg can result in only one of two daughter cells receiving the component after cell division. This asymmetry can be maintained by the cytoskeleton. It can mean that only one of the two cells will express certain genes, resulting in a difference in cell fate determination.

Question 2

What would happen if an artificial, impermeable membrane were placed between the anchor cell and the underlying cells of the developing nematode? Explain your answer.

The anchor cell would not be able to send a differentiation signal to the overlying surface tissue, so the latter would not develop into the vulva.

Question 3

Molecular biologists can attach genes to active promoters and insert them into cells. What would happen if myoD in undifferentiated myoblasts were inserted and overexpressed? Explain your answer.

The p21 gene would be activated and the cell cycle would be blocked; in the presence of other factors, muscle cells would form.

410

You have seen how cell fate is determined and examined the roles of gene expression in cell fate determination and differentiation. We will now look at how gene expression affects differentiation and morphogenesis.