Heart targeting of retroviral expression in avian embryos: a species-independent phenomenon

A replication-incompetent retroviral vector derived from spleen necrosis virus (SNV), in which the viral structural genes gag, pol, and env were replaced with the bacterial β-galactosidase gene lacZ, was used to infect embryos from outbred and inbred chicken lines, japanese quail and duck between embryonic day 0 and 13. LacZ expression was restricted to a few organs or cell types, and this distribution was not influenced by the different routes of inoculation tested but was specified by the age of the embryo at the time of inoculation. Inoculations at E0-E1 beneath or onto the blastodisc resulted in lacZ expression in ectodermal derivatives, i.e. skin and neural structures. From E2 onwards, heart muscle and skin were the preferential targets in all the species or inbred lines tested. Heart muscle was positive in 100% of the embryos displaying lacZ+ clones. Skin exhibited on and off periods depending on the age at inoculation. No lacZ-positive clones were detected in chick embryos infected after Ell. Outbred chick embryos displayed the largest array of organs labelled (heart, skin, liver, gizzard) while quail and duck embryos exhibited a more restrictive pattern. These results are of import if the vector is to be used as a tool to map lineages or to transfer genes into the developing embryo.