Chorion-deficient Mutants ?

[pvalerio at kean.ucs.mun.ca]

   I am curious to know whether anyone is currently working on, or has
considered the possibility of exploring, the following research topic with
fish embryos.
   Many people working with fish embryos need to routinely remove the chorion
as part of their experimental protocol. This can be time-consuming, and perhaps
harmful to the embryo. Is there a possibility of creating a chorion-deficient
mutant of, say a zebrafish, analogous to the cell-wall deficient algal cells
that are used by plant molecular biologists ? The rationale behind this
procedure is as follows:

1. Mechanical or enzymatic dechorionation can be harmful to 
    embryos.
2. Although the chorion may be required for osmoregulation
   (eg. by retaining colloid released during cortical
    granule breakdown), dechorionated embryos can have similar survival 
    rates in freshwater (+ marine ?) fishes.
3. Chorion-deficient embryos could be used for a variety of experiments 
   that are difficult or impossible with normal embryos: eg. cell fusion,
   gene transfer, organelle or cell ablation by lasers, other forms of
   microsurgery, etc...
4. Perhaps chorion-deficient embryos could be cryopreserved, since the 
   problem of supercooling would be circumvented by exposing the embryo
   directly to cooled cryoprotectant solutions.

   I understand that the chorion protein may be derived from more than one
cell type in the ovary, but even if a mutation could be produced that prevents
the 'hardening' process at the time of cortical granule breakdown, the 
chorions could be more easily removed. If this could be achieved with a model
species like the zebrafish, it might make life a lot easier for people working 
with other species having a very tough chorion - if the method could be 
adapted to work with other species. At the moment, many studies must involve 
more time-consuming procedures, such as microinjection through the micropyle, 
for example.

- Paul.