The testicular feminized (Tfm) mouse lacks completely androgen responsiveness; and therefore, is unique for studying the role of androgenlc steroids in different biological processes. In order to understand the molecular basis of this mutation, 2.8 kllobases of cDNA encoding the Tfm mouse androgen receptor (AR) were amplified with a polymerase chain reaction (PCR) technique. No large deletion in the coding region of the Tfm mouse AR was detected. However, sequence analysis revealed a single base deletion in the coding region of the Tfm AR mRNA. This mutation, which is located in the amino-terminus domain of the receptor, is predicted to cause a frame-shift In translation resulting in a premature termination of AR synthesis at amino acid 412. In vitro translation studies of the recomblnant wild type and Tfm AR's demonstrated that the Tfm AR cDNA failed to produce a full-length receptor. Furthermore, the Tfm AR was demonstrated to lack transcrlptional activation capability by cotransfection experiments using the Tfm AR with a reporter plasmid of mouse mammary tumor virus long terminal repeat linked to the chloramphenicol acetyltransferase gene. These studies provide evidence of the molecular defect which causes androgen insensitivity in the Tfm mouse.
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