The Questions of Developmental Biology

Principles of Development:Cell-Cell Communication
1. Inductive tissue interaction involves inducer and responding tissues.
2. The ability to respond to inductive signals depends upon the competence of the responding
cells.
3. Reciprocal induction occurs when the two interacting tissues are both inducers and are
competent to respond to each other's signals.
4. Cascades of inductive events are responsible for organ formation.
5. Regionally specific inductions can generate different structures from the same tissue.
6. The ability to respond to inducers is determined by the genetic state of the responding tissue.
7. Juxtacrine interactions are inductions that occur between the cell membranes of adjacent cells or between
a cell membrane and an extracellular matrix secreted by another cell.
8. Paracrine interactions occur when a cell or tissue secretes proteins that induce changes in neighboring
cells.
9. Paracrine factors are inducing proteins that bind to cell membrane receptors in competent responding
cells.
10. Competent cells respond to paracrine factors through signal transduction pathways. Competence is the
ability to bind and to respond to the inducers, and it is often the result of a prior induction.
11. Signal transduction pathways begin with the paracrine or juxtacrine factor causing a conformational
change in its cell membrane receptor. The new shape results in enzymatic activity in the cytoplasmic
domains of the receptor protein. This allows the receptor to phosphorylate other cytoplasmic proteins,
thereby activating a dormant kinase activity. Eventually, a transcription factor (or set of factors) is activated
that activates or represses specific gene activity.
12. Pleiotropy is the phenomenon of many phenotypic changes being caused by one mutation. Mosaic
pleiotropy results when the mutant gene is used in different parts of the body and each part is separately
altered. Relational pleiotropy occurs when a particular defect caused by the mutant gene affects other parts
of the body that do not express the gene.
13. Genetic heterogeneity results when multiple genes are needed to create a particular phenotype. Often
mutant genes for a paracrine factor cause syndromes similar to those generated by mutant genes for the
factor's receptor.
14. Phenotypic heterogeneity results when the same mutation produces different phenotypic effects in
different individuals. It is caused by the interactions between gene products.
15. Dominant mutations (in which only one mutant gene of the diploid pair is necessary to produce an
abnormal phenotype) can be caused by haploinsufficiency, gain-of-function mutations, or dominant
negative alleles.
16. Programmed cell death is one possible response to inductive stimuli. Apoptosis is a critical part of life.
17. There is cross-talk between signal transduction pathways, which allows the cell to respond to multiple
inputs simultaneously.