SEA CHROMOSOME LINKAGE OF CHICKEN AND DUCK TYPE-I INTERFERON GENES - FURTHER EVIDENCE OF EVOLUTIONARY CONSERVATION OF THE Z-CHROMOSOME IN BIRDS

Type I interferons (IFNs) are a family of proteins that are predominan tly expressed in response to viral infection. Two serologically distin ct forms of type I IFN, designated ChIFN1 and ChIFN2, have recently be en recognized in the chicken. ChIFN1 is encoded by a cluster of ten or more intronless genes, whereas ChIFN2, whose primary sequence is 57% identical, is encoded by a single intronless gene. By fluorescence in situ hybridization we now demonstrate that the genes for ChIFN1 and Ch IFN2 are all located on the short arm of the chicken Z chromosome. Thi s assignment was confirmed by results that showed that DNA from male ( ZZ) chickens yielded approximately twofold stronger Southern blot sign als with ChIFN1 and ChIFN2 hybridization probes than DNA from females (ZW). Attempts to determine differences in IFN production between male and female chickens failed owing to a high degree of variation in vir us-induced IFN expression between individuals of both sexes. Sex linka ge of IFN genes was also observed in domestic ducks: fluorescence in s itu hybridization of duck metaphase chromosomes with a duck type I IFN probe was confined to the terminal region of the long arm of the Z ch romosome. Thus, in contrast to mammals, which have their IFN genes on autosomes, birds have the type I IFN genes on the sex chromosome.