Embryonic heat conditioning in chicks induces transgenerational heat/immunological resilience via methylation on regulatory elements

Abstract

The question of whether behavioral traits are heritable is under debate. An obstacle in demonstrating transgenerational inheritance in mammals originates from the maternal environment's effect on offspring phenotype. Here, we used in ovo embryonic heat conditioning (EHC) of first-generation chicks, demonstrating heredity of both heat and immunological resilience, confirmed by a reduced fibril response in their untreated offspring to either heat or LPS challenge. Concordantly, transcriptome analysis confirmed that EHC induces changes in gene expression in the anterior preoptic hypothalamus (APH) that contribute to these phenotypes in the offspring.To study the association between epigenetic mechanisms and trait heritability, DNAmethylation patterns in the APH of offspring of control versus EHC fathers were evaluated. Genome-wide analysis revealed thousands of differentially methylated sites (DMSs), which were highly enriched in enhancers and CCCTC-binding factor (CTCF) sites. Overlap analysis revealed 110 differentially expressed genes that were associated with altered methylation, predominantly on enhancers. Gene-ontology analysis shows pathways associated with immune response, chaperone-mediated protein folding, and stress response. For the proof of concept, we focused on HSP25 and SOCS3, modulators of heat and immune responses, respectively. Chromosome conformational capture (3C) assay identified interactions between their promoters and methylated enhancers, with the strongest frequency on CTCF binding sites.Furthermore, gene expression corresponded with the differential methylation patterns, and presented increased CTCF binding in both hyper-and hypomethylated DMSs. Collectively, we demonstrate that EHC induces transgenerational thermalThis is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Molecular responses of chicken embryos to maternal heat stress through DNA methylation and gene expression

“…The results revealed a slight influence of maternal heat stress on embryo transcriptomic levels, with eleven differentially expressed genes. We detected a total of 289 DMCs between HS and CT groups, consistent with findings from previous studies in chicken 28 , cow 34 or guinea pig 35 , which have demonstrated changes in DNA methylation linked to parental heat exposure.…”

“…The copyright holder for this preprint (which this version posted April 15, 2024. ; https://doi.org/10.1101/2024.04.12.589068 doi: bioRxiv preprint environments, epigenetic factors, through intergenerational and transgenerational effects, play a role in promoting adaptability of exposed populations 33,35 . This has been observed in chicken, with an intergenerational inheritance of heat resilience after fathers' embryonic heat conditioning, associated with DNA methylation changes in anterior preoptic hypothalamus 28 .…”

“…The hypothesis made to justify the improved resistance was that heat stress-induced epigenetic modifications were occurring as a consequence of the embryonic thermal manipulation, leading to increased thermal tolerance and adaptability in adults. A recent study confirmed the epigenetic nature of the transmission of heatinduced effects between generations through epigenetic mechanisms in chicken 28 .…”

Embryonic manipulations shape life-long, heritable stress responses through complex epigenetic mechanisms: a review

“…On one hand, poor embryonic development may lead to adult adversities ( Galler and Rabinowitz, 2014 ; O’Donnell and Meaney, 2017 ). On the other hand, the embryonic environment can have a beneficial effect on improving stress tolerance ( Pribenszky et al, 2010 ; Rosenberg et al, 2022 ). Hence, understanding and optimizing embryonic conditions hold promise for not only individual survival but also for the transmission of adaptive traits across generations.…”

“…In recent years, both our team and others have pioneered the use of a chick model to investigate responses to embryonic and early-life thermal stress ( Loyau et al, 2016 ; Cramer et al, 2019 ; Rosenberg et al, 2020 , 2021 , 2022 ; Iraqi et al, 2024 ). These studies have indicated that enhancing thermotolerance in poultry is achievable through exposure to elevated ambient temperatures during embryogenesis.…”