General Interview Questions - Developmental Basics

Describe in general terms how cellular asymmetry can lead to differences in gene expression.

How are cellular asymmetries generated?

What is meant by cellular differentiation?

What is meant when we call a cell 'totipotent'?

What is induction and what role does it play in the development of an embryo? during organogensis?

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1.The generation of distinct cell types requires the generation of molecular and cellular asymmetries. A single cell can be asymmetric or polarized.

2. Cytoplasmic asymmetries can be in the form of differentially distributed RNAs or proteins, and usually both.

3. Cytoplasmic asymmetries lead to differential patterns of gene expression in the cells that come to reside in different regions of the embryo.

4. In some species, where sperm enter the egg is predetermined. In other species, the site of sperm entry serve to establish asymmetry.

5. Asymmetries can be generated by the relative positions of cells within an embryo; surface cells can differ from internal cells.

6. Differential gene expression in turn leads to altered cytoplasmic and nuclear composition. It is this process that generates differentiated cells; cells with distinct morphologies and functions within the organism.

7. Changes in chromatin organization occur during the process of differentiation can are involved in the stability of the differentiated state. These are an example of epigenetic changes.

8. Cellular asymmetries can lead to asymmetries in intercellular interactions, which in turn can stabilize or direct further cellular asymmetries.

9. Inductive interactions between cells can involve juxtacrine (direct contact, surface-mediated), paracrine (short range secreted factor-mediated) and endocrine (long range secreted factor-mediated) signaling events between cells.

10. Often interactions between groups of cells are required in order to respond to an inductive signal. Rarely do individual cells differentiate independently of their neighbors, rather groups of cells differentiate to form a tissue. This is known as the community effect.

11. Cells can respond differently to differences in level of inductive signals. This behavior underlies morphogenic/inductive gradients. These gradients can lead to new cell types and new inductive signals.

12. The regulated movement of cells and changes in cellular morphology are critical to both the patterning of inductive interactions and the process of morphogenesis during development and organ formation.

13. The timing of inductive events is critical to normal developmental events.

14. Inductive signaling is mediated by secreted factors and cell surface ligands, membrane and intracellular receptors and the intracellular signal transduction pathways that they regulate.
15.For each positively acting factor there are generally antagonists and co-factors that modulate 'signal strength' and specificity.
16. Signal transduction pathways often regulate gene expression by regulating the activity of transcription factors. Signal transduction pathway can also regulate protein activity involved in cell morphology, movement, division or survival.
17. It can be assumed that a number of inductive events underlie each aspect of embryonic development. These are not necessarily additive; they can involve complex and non-linear interactions.
18. The formation of organs, and the tissues that compose them, is based on a similar process of inductive interactions.

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