2.2. Gene transfer and ex ovo culture of the embryos
For higher gene transfer efficiency and easier embryo manipulation,ex ovoculture[14]was employed. Unlike the traditional windowing technique, theex ovomethod requires both donor eggs and
recipient eggs. The donors were fertilized eggs (stage X embryos
according to the classification, see Ref.[15]) obtained from ISA
brown laying hens that were artificially inseminated once per
week with semen from ISA brown males. Only eggs of normal
shape weighing approximately 60 g were used. The weight of a recipient egg was at least 62 g (for the first 3 days of incubation) or
90 g (for the rest of the incubation period). After swabbing the
shells with 70% alcohol, the donor egg was opened and its contents
were transferred to an empty recipient eggshell drilled to create a
window (a circular hole, 33 mm in diameter) at the blunt end.
DMEM (5ll) containing concentrated virus and 10lg/ml polybrene was injected into the central part of the subgerminal cavity
using a microinjection pipette before the egg was covered with
additional ovalbumin and sealed with plastic wrap. After microinjection, the sealed eggs were incubated at 37.5C and 60% relative
humidity with a 90rocking motion every 15 min for 3 days. The
embryos were transferred to larger empty recipient eggshells with
a 42-mm circular window and incubated at 37C and 70% relative
humidity with a rocking motion every 30 min through a 30angle
for an additional 15 days. The rocking motion was stopped after
18 days of incubation, and the eggs were allowed to hatch after
replacing the plastic wrap covering the window with a 55-mm Petri dish lid after 20 or 20.5 days of incubation.