Type II gonadotropin-releasing hormone receptor transcripts in human sperm

Area of Science:

• Reproductive biology
• Molecular endocrinology
• Genomics

Background:

• Gonadotropin-releasing hormone (GnRH) primarily acts through the type I receptor in the pituitary gland to regulate reproduction.
• Two homologous genes for a second GnRH receptor (type II) exist in the human genome: one on chromosome 14 and another on chromosome 1.
• The chromosome 14 gene is highly transcribed but lacks essential coding elements, while the chromosome 1 gene contains all exons but its functionality is uncertain.

Purpose of the Study:

• To determine if the human chromosome 1 GnRH receptor type II gene is transcribed in human tissues.
• To investigate whether these transcripts can encode a functional receptor protein.
• To clarify the potential role of GnRH receptor type II in human reproduction.

Main Methods:

• Screening of human RNAs using hybridization techniques.
• Reverse transcription polymerase chain reaction (RT-PCR) to detect gene expression.
• In situ hybridization to localize transcripts within specific cells.
• Sequence analysis of the identified transcripts.

Main Results:

• Chromosome 1 GnRH receptor type II gene expression is limited and of low abundance compared to the chromosome 14 gene.
• Transcripts containing exon 1 were detected in mature sperm and human postmeiotic testicular cells.
• Human transcripts contain a stop codon and a frame-shift mutation, suggesting they may be pseudogenes.
• Despite potential pseudogene status, a functional type II GnRH receptor has been cloned from monkeys.

Conclusions:

• The human chromosome 1 GnRH receptor type II gene is transcribed, particularly in testicular cells and sperm.
• Transcripts possess sequence anomalies (stop codon, frame-shift) that challenge their ability to produce a functional receptor.
• Given evidence from other mammals and human tissues, the functional significance of the human chromosome 1 gene warrants further investigation.