Influence of the Temperature and the Genotype of the HSP90AA1 Gene over Sperm Chromatin Stability in Manchega Rams

Abstract

The present study addresses the effect of heat stress on males' reproduction ability. For that, we have evaluated the sperm DNA fragmentation (DFI) by SCSA of ejaculates incubated at 37°C during 0, 24 and 48 hours after its collection, as a way to mimic the temperature circumstances to which spermatozoa will be subject to in the ewe uterus. The effects of temperature and temperature-humidity index (THI) from day 60 prior collection to the date of semen collection on DFI were examined. To better understand the causes determining the sensitivity of spermatozoa to heat, this study was conducted in 60 males with alternative genotypes for the SNP G/C−660 of the HSP90AA1 promoter, which encode for the Hsp90α protein. The Hsp90α protein predominates in the brain and testis, and its role in spermatogenesis has been described in several species. Ridge regression analyses showed that days 29 to 35 and 7 to 14 before sperm collection (bsc) were the most critical regarding the effect of heat stress over DFI values. Mixed model analyses revealed that DFI increases over a threshold of 30°C for maximum temperature and 22 for THI at days 29 to 35 and 7 to 14 bsc only in animals carrying the GG−660 genotype. The period 29–35 bsc coincide with the meiosis I process for which the effect of the Hsp90α has been described in mice. The period 7–14 bsc may correspond with later stages of the meiosis II and early stages of epididymal maturation in which the replacement of histones by protamines occurs. Because of GG−660 genotype has been associated to lower levels of HSP90AA1 expression, suboptimal amounts of HSP90AA1 mRNA in GG−660 animals under heat stress conditions make spermatozoa DNA more susceptible to be fragmented. Thus, selecting against the GG−660 genotype could decrease the DNA fragmentation and spermatozoa thermal susceptibility in the heat season, and its putative subsequent fertility gains.

Differences in the Ovine HSP90AA1 Gene Expression Rates Caused by Two Linked Polymorphisms at Its Promoter Affect Rams Sperm DNA Fragmentation under Environmental Heat Stress Conditions

“…As a way to examine the role of -660G/C and -668insC polymorphisms on the observed effect of heat on sperm chromatin integrity [ 15 , 16 ], climate and sperm DNA status data were gathered from March to October.…”

“…Animals (61 rams selected from the 120 used in the expression analyses), biological samples, environmental conditions and sperm DNA fragmentation assay (SCSA) data were those used in the work of Ramón and colleagues [ 15 ]. Briefly, a total of 7 collections per male were carried out, from March to October as a way to ensure that sperm were exposed to different environmental conditions of temperature and humidity.…”

“…Proper compaction and structure of DNA has been reported to have important functional roles, being essential for DNA replication and embryonic development [ 13 , 14 ]. In a recent work of our group [ 15 ] it has been observed that sperm DNA fragmentation in rams increases over a threshold of 30°C of maximum temperature (temperature-humidity index THI > 22) at some stages of the spermatogenesis process in animals carrying the GG -660 genotype of the -660G/C SNP (rs397514116). As GG -660 genotype has been associated to lower levels of HSP90AA1 expression under heat stress conditions [ 16 ] it has been suggested that suboptimal amounts of HSP90AA1 mRNA make spermatozoa DNA of these animals more susceptible to be fragmented.…”

“…At the promoter of this gene 14 polymorphisms (11 SNPs and 3 INDELs) have been described [ 17 , 19 ]. One of these mutations, -660G/C SNP (rs397514116), have been related with the scrapie incubation period [ 18 ]; the adaptation of this species to differential thermal conditions [ 20 ]; and as noted above, ram’s sperm DNA fragmentation levels [ 15 ]. All these facts, which have been observed under thermoneutral, heat stress and missfolding stress conditions, seem to be consequence of the differences in the gene expression profile caused by this SNP located at the gene promoter [ 16 , 20 ].…”

Understanding Sperm Heterogeneity: Biological and Practical Implications

“…Many environmental agents such us temperature (Ramón et al. ), nutrition (Marin‐Guzman et al. ), ecotoxins and pollutants (Somers et al.…”