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

Abstract

Cloning and sequencing of the chicken prolactin receptor (PRLR) gene segment 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 findings indicate that the box 1-containing 5′-truncated transcripts are generated by the utilization of TSE-1 as the first exon with distinct splicing donor 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 initiation sites for the box 1-containing 5′-truncated transcripts and two transcription initiation sites for the box 1-lacking transcript were detected by the 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, accompanying the decrease of the amount of the canonical full-length transcript for PRLR.