Maternal genetic intergenerational and transgenerational effects on hormone synthesis in ovarian granulosa cells of offspring exposed to cadmium during pregnancy

This study aimed to investigate the maternally inherited intergenerational and transgenerational effects of cadmium (Cd) exposure on steroid hormone synthesis in the ovarian granulosa cells (GCs) of offspring rats. F1 rats were obtained by mating adult female Sprague-Dawley rats with healthy adult male rats and were exposed to 0, 0.5, 2.0, and 8.0 mg/kg CdCl2 during pregnancy. The adult female rats (PND 56) were mated with healthy adult male rats to produce F2 and F3 rats. The serum progesterone (Pg) and estradiol (E2) levels of the F2 adult female rats were decreased, while those of F3 rats were significantly increased. Moreover, hormone synthesis-related genes had different expression patterns in the F2 and F3 generations. F2 and F3 rat ovarian GCs exhibited altered miRNA expression profiles and DNA methylation patterns. Validation of miRNAs that regulate hormone synthesis-related genes in the cAMP/PKA signaling pathway suggested that miR-124-3p was downregulated in F2 and F3 rats, while miR-133a-5p and miR-150-5p were upregulated in F2 rats and downregulated in F3 rats. In summary, 1) there are maternal genetic intergenerational (GCs hormone synthesis disorder) and transgenerational (GCs hormone synthesis function repair change) effects on hormone synthesis function changes in offspring GCs induced by Cd exposure during pregnancy. 2) Changes in miRNAs and DNA methylation modifications associated with the genetic effects of altered hormone synthesis function in offspring GCs induced by Cd exposure during pregnancy are important. 3) Under the current environmental level of Cd exposure, the possible risk of maternal genetic intergenerational and transgenerational effects of offspring ovarian toxicity should be strongly considered.

Both indirect maternal and direct fetal genetic effects reflect the observational relationship between higher birth weight and lower adult bone mass

BACKGROUND

Birth weight is considered not only to undermine future growth, but also to induce lifelong diseases; the aim of this study is to explore the relationship between birth weight and adult bone mass.

METHODS

We performed multivariable regression analyses to assess the association of birth weight with bone parameters measured by dual-energy X-ray absorptiometry (DXA) and by quantitative ultrasound (QUS), independently. We also implemented a systemic Mendelian randomization (MR) analysis to explore the causal association between them with both fetal-specific and maternal-specific instrumental variables.

RESULTS

In the observational analyses, we found that higher birth weight could increase the adult bone area (lumbar spine, β-coefficient= 0.17, P < 2.00 × 10^-16; lateral spine, β-coefficient = 0.02, P = 0.04), decrease bone mineral content-adjusted bone area (BMCadjArea) (lumbar spine, β-coefficient= - 0.01, P = 2.27 × 10^-14; lateral spine, β-coefficient = - 0.05, P = 0.001), and decrease adult bone mineral density (BMD) (lumbar spine, β-coefficient = - 0.04, P = 0.007; lateral spine; β-coefficient = - 0.03, P = 0.02; heel, β-coefficient = - 0.06, P < 2.00 × 10^-16), and we observed that the effect of birth weight on bone size was larger than that on BMC. In MR analyses, the higher fetal-specific genetically determined birth weight was identified to be associated with higher bone area (lumbar spine; β-coefficient = 0.15, P = 1.26 × 10^-6, total hip, β-coefficient = 0.15, P = 0.005; intertrochanteric area, β-coefficient = 0.13, P = 0.0009; trochanter area, β-coefficient = 0.11, P = 0.03) but lower BMD (lumbar spine, β-coefficient = - 0.10, P = 0.01; lateral spine, β-coefficient = - 0.12, P = 0.0003, and heel β-coefficient = - 0.11, P = 3.33 × 10^-13). In addition, we found that the higher maternal-specific genetically determined offspring birth weight was associated with lower offspring adult heel BMD (β-coefficient = - 0.001, P = 0.04).

CONCLUSIONS

The observational analyses suggested that higher birth weight was associated with the increased adult bone area but decreased BMD. By leveraging the genetic instrumental variables with maternal- and fetal-specific effects on birth weight, the observed relationship could be reflected by both the direct fetal and indirect maternal genetic effects.

Maternal genetic effects in Astyanax cavefish development

The role of maternal factors in the evolution of development is poorly understood. Here we describe the use of reciprocal hybridization between the surface dwelling (surface fish, SF) and cave dwelling (cavefish, CF) morphs of the teleost Astyanax mexicanus to investigate the roles of maternal genetic effects in cavefish development. Reciprocal hybridization, a procedure in which F1 hybrids are generated by fertilizing SF eggs with CF sperm (SF × CF hybrids) and CF eggs with SF sperm (CF × SF hybrids), revealed that the CF degenerative eye phenotype showed maternal genetic effects. The eyes of CF × SF hybrids resembled the degenerate eyes of CF in showing ventral reduction of the retina and corresponding displacement of the lens within the optic cup, a smaller lens and eyeball, more lens apoptosis, a smaller cartilaginous sclera, and lens-specific gene expression characteristics compared to SF × CF hybrids, which showed eye and lens gene expression phenotypes resembling SF. In contrast, reciprocal hybridization failed to support roles for maternal genetic effects in the CF regressive pigmentation phenotype or in CF constructive changes related to enhanced jaw development. Maternal transcripts encoded by the pou2f1b, runx2b, and axin1 genes, which are involved in determining ventral embryonic fates, were increased in unfertilized CF eggs. In contrast, maternal mRNAs encoded by the ß-catenin and syntabulin genes, which control dorsal embryonic fates, showed similar expression levels in unfertilized SF and CF eggs. Furthermore, maternal transcripts of a sonic hedgehog gene were detected in SF and CF eggs and early cleaving embryos. This study reveals that CF eye degeneration is controlled by changes in maternal factors produced during oogenesis and introduces A. mexicanus as a model system for studying the role of maternal changes in the evolution of development.

Social Interactions and Indirect Genetic Effects on Complex Juvenile and Adult Traits

Most animal species are social in one form or another, yet many studies in rodent model systems use either individually housed animals or ignore potential confounds caused by group housing. While such social interaction effects on developmental and behavioral traits are well established, the genetic basis of social interactions has not been researched in as much detail. Specifically, the effects of genetic variation in social partners on the phenotype of a focal individual have mostly been studied at the phenotypic level. Such indirect genetic effects (IGEs), where the genotype of one individual influences the phenotype of a second individual, can have important evolutionary and medically relevant consequences. In this chapter, we give a brief outline of social interaction effects, and how systems genetics approaches using recombinant inbred populations can be used to investigate indirect genetic effects specifically, including maternal genetic effects. We discuss experimental designs for the study of IGEs and show how indirect genetic loci can be identified that underlie social interaction effects, their mechanisms, and consequences for trait variation in focal individuals.