Two novel first exons in the prolactin receptor gene are transcribed in a tissue-specific and sexual maturation-dependent manner to encode multiple 5'-truncated transcripts in the testis of the chicken

Cloning and sequencing of the chicken prolactin receptor (PRLR) gene segmen t from the transmembrane domain to the box 2 motif revealed the presence of the two testis-specific first exons, TSE-1 and TSE-2, encoding the unique 5'-end sequences of the reported and newly identified multiple 5'-truncated PRLR transcripts containing only the cytoplasmic domain in the testis. TSE -1 was located downstream of the exon encoding the transmembrane domain and TSE-2 presented downstream of the exon encoding the box 1 motif. These fin dings indicate that the box 1-containing 5'-truncated transcripts are gener ated by the utilization of TSE-1 as the first exon with distinct splicing d onor sites to the box 1-containing exon, and that the utilization of TSE-2 as the first exon and its splicing to the box 2-containing exon results in the generation of the box 1-lacking transcript. Three transcription initiat ion sites for the box 1-containing 5'-truncated transcripts and two transcr iption initiation sites for the box 1-lacking transcript were detected by t he RNase protection assays. Reverse transcription-polymerase chain reaction analysis showed that the expression levels of all these 5'-truncated PRLR transcripts are simultaneously increased during sexual maturation, accompan ying the decrease of the amount of the canonical full-length transcript for PRLR. (C) 2000 Elsevier Science B.V. All rights reserved.