Re: What do developmental biologists mean by ' dominant negative?'

Developmental biologists use the term dominant-negative to describe a gene 
or 
protein which has a dominant effect similar to that described genetically, 
i.e. one copy of the gene gives a mutant phenotypic effect, and a negative 
effect in that it prevents or has a negative impact on a biological process 
such as a signal transduction pathway.  This is most easily described in a 
protein that functions as a dimer or multimer.  If one part of that protein 
complex is mutant in some functional aspect of the multimer but is still 
able to form the multimer it has a dominant affect on the other wildtype 
portions of the complex, and a negative effect if the mutation prevents the 
complex from carrying out its normal function.  In this case the gene that 
codes for the mutant monomer component of the protein complex can be called 
a dominant-negative gene, and the protein it forms is a dominant-negative 
protein.  For example, activin type receptors form dimers between type I 
and type II receptors to transduce a signal from an extracellular ligand 
into the cell.  A dominant-negative activin receptor has one monomer unit 
which lacks the intracellular domain necessary for signal transduction.  
This can still form the dimer receptor, but the signal is not transduced.  
To read about effects of the truncated activin receptor see Nature 359:609-
614.