MOLECULAR-BASIS OF NANOMELIA, A HERITABLE CHONDRODYSTROPHY OF CHICKEN

Nanomelia is a recessively inherited connective tissue disorder of chi cken affecting cartilage development. Other investigators have demonst rated that it involves low aggrecan production and diminished aggrecan mRNA levels. Based on genetic linkage studies showing a high likeliho od that the mutation responsible for the nanomelic phenotype lay withi n the aggrecan gene, a series of experiments was performed to define t he molecular basis of the trait. Aggrecan mRNA was present in the nucl eus of the nanomelic chondrocyte but greatly reduced in the cytoplasmi c compartment, a finding suggestive of a premature stop codon within t he aggrecan transcript. Since no defect in mRNA splicing could be demo nstrated by ribonucleasease protection studies, direct DNA sequencing was initiated by polymerase chain reaction of the mRNA and of genomic DNA. A stop codon was demonstrated at codon 1513, which is located in the eighth repeat of the chondroitin sulfate 2 domain of the large ten th exon. The mutation creates a unique BasBI restriction site which re adily distinguishes the mutant and wild-type alleles.