Molecular Analysis of Endogenous Virus ev 21-Slow Feathering Complex of Chickens.

Abstract

Sex-linked slow-feathering gene, K, is genetically associated with the presence of an avian endogenous retrovirus ev21 in White Leghorns (WL). An EcoRI fragment corresponding to the endogenous virus ev21-cell junction fragment and a fragment homologous to the proviral unoccupied site (US) were cloned, respectively, from genomic DNA libraries of two WL chickens: an ev21-only female and an ev-negative male. A 1.7-kilobase pairs (kbp) fragment cleaved from the cloned proviral US by the HaeIII restriction endonuclease was the most informative probe to molecularly characterize the occupied and unoccupied integration sites of ev21 locus. Restriction fragment length polymorphism analysis of slow-feathering (SF) and rapid-feathering (RF) chickens from various commercial breeds, using the US HaeIII 1.7-kbp probe, indicated that the complete genetic association between ev21 and SF phenotype is common among other lines of SF chickens and was not restricted to WL. It was also shown that there was at least one additional DNA region highly homologous to DNA sequences flanking the EV21 integration site in the chicken genome. In SF birds of either sex this additional repeat was distinguishable from the site occupied by ev21 (OR) and represents an unoccupied repeat (UR). Analysis of DNA from RF revertant females showed novel patterns of reversion. In Type I RF revertants, RF is associated with the complete excision of proviral ev21 DNA sequences. In Type II revertants, the UR homologous to the cell sequences flanking ev21 integration site is excised, but proviral ev21 sequences remain intact. A hypothesis to explain these types of reversion is suggested. It postulates a close association between OR and UR on the Z chromosome.

Endogenous Viral Gene Distribution in Populations of Meat-Type Chickens

“…The pRAV-2 probe is a pBR322 plasmid containing most of the DNA equivalent to the exogenous ALV genome (Smith and Crittenden, 1986). For detection of ep21, the pEV21-int 5 probe specific for this locus (Levin and Smith, 1990) was used. Experimental procedures were as described previously (Kuhnlein et al, 1989a).…”

Association between in vitro heterophil function and the feathering gene in commercial broiler chickens

“…There is evidence to indicate slow feathering (SF) is a result of the incorporation of an endogenous retrovirus (EV) into the genome and that the feathering and ev21 genes are tightly linked (Bacon et al, 1988;Levin & Smith, 1990). Genes that affect the feathering rate have been identified in Leghorns (Levin & Smith, 1990), broilers (Sabour et al, 1992), turkeys (Asmundson & Abbott, 1961), and guinea fowl (Pal & Singh, 1997). There is evidence to suggest EV incorporations can adversely affect the immune competence of chickens.…”

Determination of avian endogenous provirus ‐ cellular junction sequences using inverse polymerase chain reactions

“…To determine if amplimers represented regions between the primers, a series of Southern blots were hybridized to M P labeled plasmids that contained either U3N or the ev21 unoccupied integration site (USIL) (Levin and Smith, 1990). Southern blotting and hybridizations were previously described (Levin and Smith, 1990).…”