DEVELOPMENTAL GENETICS AND ENHANCER TRAPS

What do you need to remember about developmental genetics?

1) Different cells, and cells in different positions, are different because they express different combinations of genes.

2) How do cells end up expressing different combinations of genes? There are 2 main reasons: 

a) they inherit different cytoplasmic determinants (for example, if in a cell a particular protein is not evenly distributed throughout the cytoplasm, the 2 daughter cells will inherit different concentrations of this protein). In the special cases of embryos that at some point are like the Drosophila one, with many nuclei in a big communal cytoplasm, if a morphogen is distributed unevenly  in the communal cytoplasm, then nuclei in different regions will be exposed to different concentrations of the morphogen. The net result of inheriting, or being exposed to, different concentrations of morphogens is that different genes will be expressed at different levels;

b) cells communicate with each other and with their environment; cell-to-cell communication, and cell-to-environment communication is transduced into signalling cascades, resulting in expression of particular subsets of genes.

3) How can we have uneven distribution of an RNA or of a protein in the cytoplasm? Again, there are a number of ways. We can anchor the RNA to a particular spot, so that when it is translated, the protein product will diffuse from this source and thus form a concentration gradient. We can also constantly, actively transport the RNA or the protein product to one region of the cytoplasm. We can let the RNA get evenly distributed, but have a protein, localized in one specific region and forming a bit of a concentration gradient, that prevents its translation. This will create a 'sink' and therefore a concentration gradient of the protein product of our RNA.

4) Remember maternal effect genes! Remember that at the earliest stages, a zygote does not transcribe/translate its own genes. It 'lives off' the products that the mother dumped in the egg's cytoplasm. 

FOR ENHANCER TRAPS

Here are a few links that, are better than any explanations I gould give, and also give lots of example of how people use these great tools:

http://www.biochem.northwestern.edu/holmgren/Glossary/Definitions/Def-E/enhancer_trap.html

Example of uses (just read the abstracts to get an idea!):

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T39-3YXJ34N-H&_user=1022551&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=965372155&_rerunOrigin=google&_acct=C000050484&_version=1&_urlVersion=0&_userid=1022551&md5=61b5e2743be61fd22e71815ae982073f

http://www.ncbi.nlm.nih.gov/pubmed/8049476

Promoter traps (have a look at the abstract):

http://www.pnas.org/content/103/47/17813.full