Genetic mapping of the cloned subgroup A avian sarcoma and leukosis virus receptor gene to the TVA locus

Abstract

A chicken gene conferring susceptibility to subgroup A avian sarcoma and leukosis viruses (ASLV-A) was recently identified by a gene transfer strategy. Classical genetic approaches had previously identified a locus, TVA, that controls susceptibility to ASLV-A. Using restriction fragment length polymorphism (RFLP) mapping in inbred susceptible (TVA*S) and resistant (TVA*R) chicken lines, we demonstrate that in 93 F2 progeny an RFLP for the cloned receptor gene segregates with TVA. From these analyses we calculate that the cloned receptor gene lies within 5 centimorgans of TVA, making it highly probable that the cloned gene is the previously identified locus TVA. The polymorphism that distinguishes the two alleles of TVA in these inbred lines affects the encoded amino acid sequence of the region of Tva that encompasses the viral binding domain. However, analysis of the genomic sequence encoding this region of Tva in randomly bred chickens suggests that the altered virus binding domain is not the basis for genetic resistance in the chicken lines analyzed.

FIG. 1

RFLP mapping of the cloned receptor gene. Genomic DNA from the parental lines, 7₂ and 6₃, and 18 F₂ progeny was digested with TaqI and then analyzed by Southern blotting with a random-primer-labeled 375-bp probe specific for the cloned ASLV-A receptor gene. The approximate sizes (in kilobases) of the two hybridizing fragments are indicated. The susceptibility of the F₂ progeny to ASLV-A infection is indicated. R, resistant; S, sensitive.

FIG. 2

Sequence analysis of the viral interaction region in the ALSV-A receptor. (A) The viral interaction region from the ASLV-A receptor gene in lines 6₃ and 7₂ was amplified by PCR and the DNA sequence was determined. The deduced amino acid sequence and DNA sequence for line 6₃ are shown in the top lines. Nucleotide differences between the two chicken lines are indicated by capital letters, and dots represent identical sequences. For line 7₂, only the altered amino acid residues are shown. The polymorphic TaqI site is underlined. (B) The viral interaction region of the receptor gene from genomic DNA of randomly bred broiler-type chickens was amplified by PCR and directly sequenced. The deduced amino acid sequence and susceptibility to ASLV-A infection are shown compared to the line 6₃ sequence. Dots indicate identical residues. R, resistant to ASLV-A; S, sensitive to ASLV-A. C/O represents the sequence of the functional ASLV-A receptor gene identified by gene transfer (19).