A DELETED RETROVIRAL INSERTION AT THE EV21-K COMPLEX LOCUS IN INDONESIAN CHICKENS

Very poor feather development has been observed in chickens of the Nun ukan strain, originating from Indonesia. The wing of the newly hatched chick does not show any primary or covert feathers; this phenotype wi ll be referred to as very-late feathering (VLF). As adults, chickens a re feathered but tail feathers are short and fragile. An experimental population was set up at the National Institute of Agronomic Research (INRA), Jouy-en-Josas, from one Nunukan male and four Nunukan females. Preliminary observations did not support the hypothesis of a sex-link ed dominant mode of inheritance for the VLF phenotype. A restriction f ragment length polymorphism (RFLP) study using five restriction enzyme s and two probes, RAV-2 and endogenous virus (ev) ev21-int specific fo r the endogenous viral locus ALVE21, showed the presence of the expect ed 3' junction fragments for the ev21 occupied site but failed to reve al the expected 5' junction fragments for ev21 in Nunukan chickens. Th e unoccupied site corresponded to the ev21 unoccupied repeat (UR) of t ype a (URa). A deletion in the 5' region of the provirus and of the in sertion site was indicated by the RFLP analysis and confirmed by a PCR study. Primers were designed in order to amplify a 5' junction fragme nt specific to the modified ev21 found in the Nunukan chickens. The se quence of this amplified product showed that the deletion started 652 bp upstream of the insertion site of ev21 and ended within the pol gen e of the viral genome. This deletion represents a new allele, OSD, at the ev21 insertion site (locus ALVE21), that appears insufficient to p roduce a complete virus. Current data do not show a clear causal relat ionship between OSD and the VLF phenotype. The presence of OSD may be required but is not in itself sufficient to obtain the VLF phenotype. The genetic relationships between OSD and the altered feathering pheno type of Nunukan chickens will be investigated further in families segr egating for the VLF phenotype, using the locus-specific PCR test devel oped as part of this study.