Abstract
Heat shock (HS) is one of the best-studied exogenous cellular stresses. Almost all tissues, cell types, metabolic pathways and biochemical reactions are affected in greater or lesser extent by HS. However, there are some especially thermo sensible cellular types such as the mammalian male germ cells. The present study examined the role of three INDELs in conjunction with the -660G/C polymorphism located at the HSP90AA1 promoter region over the gene expression rate under HS. Specially, the -668insC INDEL, which is very close to the -660G/C transversion, is a good candidate to be implied in the transcriptional regulation of the gene by itself or in a cooperative way with this SNP. Animals carrying the genotype II-668 showed higher transcription rates than those with ID-668 (FC = 3.07) and DD-668 (FC = 3.40) genotypes for samples collected under HS. A linkage between gene expression and sperm DNA fragmentation was also found. When HS conditions were present along or in some stages of the spermatogenesis, alternative genotypes of the -668insC and -660G/C mutations are involved in the effect of HS over sperm DNA fragmentation. Thus, unfavorable genotypes in terms of gene expression induction (ID-668GC-660 and DD-668GG-660) do not produce enough mRNA (stored as messenger ribonucleoprotein particles) and Hsp90α protein to cope with future thermal stress which might occur in posterior stages when transcriptional activity is reduced and cell types and molecular processes are more sensible to heat (spermatocytes in pachytene and spermatids protamination). This would result in the impairment of DNA packaging and the consequent commitment of the events occurring shortly after fertilization and during embryonic development. In the short-term, the assessment of the relationship between sperm DNA fragmentation sensitivity and ram’s fertility will be of interest to a better understanding of the mechanisms of response to HS and its consequences on animal production and reproduction performance.
Highlights
Heat shock (HS, known as heat stress or hyperthermia) is one of the best-studied exogenous cellular stresses
To assess the effect of heat load on sperm DNA integrity of animals carrying alternative genotypes for the polymorphisms studied, we have examined the relationship among total DNA fragmentation index (tDFI) values and average temperature-humidity index (THI), as suggested in Ramon et al [15]
The sensitivity of mammalian germ cells to environmental heat stress has been extensively studied [28, 29]. Cellular consequences of this stressor are protein miss-folding, DNA damaging, inhibition of DNA repair systems [30], and the inhibition of multiple processes associated with DNA replication [31,32,33] and the maturation of chromatin [34, 35]
Summary
Heat shock (HS, known as heat stress or hyperthermia) is one of the best-studied exogenous cellular stresses. The cellular response to HS utilizes ancient molecular networks that are based primarily on the action of stress-induced heat shock proteins (HSP) and heat shock factors. Members of the HSP90 gene family have undergone major duplication events, which led to two known cytoplasmic isoforms, namely Hsp90a ( named Hsp90AA1) or inducible form and Hsp90b ( named Hsp90AB1) which is the constitutive one. Whereas Hsp90b is more or less constitutively and ubiquitously expressed, the expression of Hsp90a is heat-inducible and more tissue specific [2]. The transcriptional enhancement of Hsp90a is mainly due to the HSF1 (heat shock factor 1), but many other heat stress related transcription factors regulate gene expression in response to environmental stress [1, 4]
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