Identification of Genetic Variation in the 5′ and 3′ Non-coding Regions of the Protamine Genes in Patients with Protamine Deregulation

Abstract

Deregulation of sperm nuclear protamine ratio (P1/P2) has been shown to correlate with male factor infertility in humans, but the cause of this abnormal protein expression has yet to be identified. Recent studies have shown that there is little genetic variability in the coding regions of either of the protamine gene sequences. However, these studies did not investigate the 5′ or 3′ non-coding regions of these genes for mutations that might account for changes in the transcriptional or translational regulation of the protamines.

In an effort to determine if genetic variation in these non-coding regions may account for aberrant protamine expression, we have sequenced the 5′ and 3′ untranslated regions (UTRs) of both protamine 1 (P1) and protamine 2 (P2) genes in a population of infertile men with protamine deregulation, men presenting for infertility work-up with normal protamine ratios, and a population of unrelated, fertile men from the Utah Genetic Reference Project (UGRP). This analysis has identified 14 single nucleotide polymorphisms (SNPs), of which 13 were novel SNPs in the UTRs of P1 and P2, and verified the existence of a variable length repeat (VLR), GA_n, in the P2 5′ region. The SNP frequencies and VLR allelic frequencies did not achieve statistical significance between the populations, however, one of the SNPs identified in the 3′ UTR of protamine 2 was found at a low frequency in the abnormal protamine patients, but was completely absent in men with verified normal protamine ratio and donors of known fertility.

In conclusion, a number of SNPs have been reported in the protamine genes and the untranslated regions, however, these gene variants do not appear to be responsible for protamine deficiency. Hence, the underlying cause for aberrant protamine expression may possibly be due to abnormalities in candidate spermatogenic transcriptional/translational regulators, post-translational modifiers, or as-of-yet unidentified factors affecting the testicular environment.

KEYWORDS:

• Infertility
• Protamine
• Spermatogenesis
• Transcription
• Translation

Notes

Abbreviations: UGRP: Utah Genetic Reference Program; UTRs: untranslated regions; VLR: variable length repeat; SNP: Single Nucleotide Polymorphism.