Maternal effects, paternal effects, and their interactions in the freshwater snail Physa acuta

Individuals exposed to predation risk can produce offspring with altered phenotypes. Most work on predation-induced parental effects has focused on maternal effects or on generalized parental effects where both parents are exposed to risk. We conducted an experiment to measure and compare maternal and paternal effects on offspring phenotypes and test for interactions in those effects. We exposed 82 snails from 22 lines to control or predator cues and created line dyads with the four possible mating pairings of control and predator cue exposed individuals. We measured the resulting body masses, shell masses, shell shapes, and anti-predator behaviors of the offspring. We found some evidence that offspring were larger and heavier when the mother was exposed to predation cues, but that this effect was negated when the father was also exposed. The mass of offspring shells relative to their total mass was unaffected by parental treatments. Shell shape was marginally affected by maternal treatment, but not paternal treatment. Behavioral responses to cues were not affected by maternal or paternal treatments. Our results suggest potential conflict between male and female parental effects and highlight the importance of examining the interactions of maternal and paternal effects.

Paternal effect does not affect in vitro embryo morphokinetics but modulates molecular profile

The use of different sires influences in vitro embryo production (IVP) outcome. Paternal effects are observed from the first cleavages until after embryonic genome activation (EGA). Little is known about the mechanisms that promote in vitro fertility differences, even less about the consequences on embryo development. Therefore, this study aimed to evaluate the paternal effect at fertilization, embryo developmental kinetics, gene expression and quality from high and low in vitro fertility bulls. A retrospective analysis for bull selection was performed using the In vitro Brazil company database from 2012 to 2015. The dataset was edited employing cleavage and blastocyst rates ranking a total of 140 bulls. Subsequently, the dataset was restricted by embryo development rate (blastocyst/cleaved rate) and ten bulls were selected as high (HF; n = 5) and low (LF; n = 5) in vitro fertility groups. IVP embryos derived from high and low fertility bulls were classified according to their stage of development (2 cells, 3-4 cells, 6 cells, 8-16 cells), at 24, 36, 48, 60, 72 hpi, respectively, to evaluate embryo kinetics. Pronuclei formation (24 hpi), cleavage rate (Day 3), development rate, and blastocyst morphology (Grade I and II - Day 7) were also assessed, as well as the abundance of 96 transcripts at 8-16 cell stage and blastocysts. There was no difference in early embryo kinetics (P > 0.05), and cleavage rate (HF = 86.7%; LF = 84.9%; P = 0.25). Nevertheless, the fertilization rate was higher on HF (72%) than LF (62%) and the polyspermy rate was lower on HF compared to LF (HF:16.2% LF:29.2%). As expected, blastocyst rate (HF = 29.4%; LF = 16.0%; P < 0.0001) and development rate (HF = 33.9% LF = 18.9%; P < 0.0001) were higher in HF than LF. At the 8-16 cell stage, 22 transcripts were differentially represented (P ≤ 0.05) between the two groups. Only PGK1 and TFAM levels were higher in HF while transcripts related to stress (6/22, ∼27%), cell proliferation (6/22, ∼27%), lipid metabolism genes (5/22, ∼23%), and other cellular functions (5/22, ∼23%) were higher on LF embryos. Blastocysts had 9 differentially represented transcripts (P ≤ 0.05); being only ACSL3 and ELOV1 higher in the HF group. Lipid metabolism genes (3/9, 33%) and other cellular functions (6/9, 67%) were higher in the LF group. In conclusion, the timing of the first cleavages is not affected by in vitro bull fertility. However, low in vitro fertility bulls presented higher polyspermy rates and produced 8-16 cells embryos with higher levels of transcripts related to apoptosis and cell damage pathways compared to high in vitro fertility ones. Evidence such as polyspermy and increase in apoptotic and oxidative stress genes at the EGA stage suggest that embryo development is impaired in the LF group leading to the reduction of blastocyst rate.

Effects of paternal diet and antioxidant addition to the semen extender on bovine semen characteristics and on the phenotype of the resulting embryo

The aim of this study was to examine the effects of long-term dietary supplementation of young Nellore bulls with rumen-protected polyunsaturated fatty acids (PUFAs) and of the inclusion of catalase in the semen extender on semen quality, in vitro sperm fertilizing ability, and intracytoplasmic lipid content in the resulting embryos. Twelve Nellore bulls were supplemented with rumen-protected PUFAs or with a basal diet from 14 to 24 months of age. The semen was collected at the end of supplementation. For cryopreservation, the ejaculate was divided into two equal volumes and catalase was added to the extender in one of the fractions. Thus, the experimental design consisted of a 2 × 2 factorial scheme with two diets (control and PUFA) and two extenders (Cat+ and Cat-). Total motility and the percentage of rapid cells in fresh semen were negatively affected by dietary supplementation with PUFAs (P < 0.05), but these effects did not persist after freezing. The frozen/thawed semen of animals fed PUFAs exhibited an increase in the percentages of damaged plasma and acrosomal membranes, as well as an increase in the proportion of lipids ions at m/z 578 and m/z 757 detected by MALDI-MS. Nevertheless, there was no effect of the treatments on in vitro embryo development. However, embryos derived from bulls supplemented with PUFAs exhibited higher lipid accumulation compared to control (P < 0.05). In conclusion, PUFA supplementation promoted worsening of semen quality without affecting the in vitro sperm fertilizing ability; however, the paternal diet affected the intracytoplasmic lipid content in the resulting embryos.

Paternal systemic inflammation induces offspring programming of growth and liver regeneration in association with Igf2 upregulation

Recent studies suggest that stress can lead to variations in offspring development. However, whether paternal systemic inflammation induces phenotypic changes in the offspring remains unclear. Here, we established an in vivo mouse model of systemic inflammation and investigated the long-term consequences on the offspring. Male, but not female offspring derived from inflammatory fathers (LPS-F1) grew faster than those derived from the control fathers (CON-F1). Moreover, the LPS-F1 males had higher capacity for liver regeneration after injury, as indicated by decreased hepatic fibrosis, apoptosis, and increased hepatocyte proliferation upon carbon tetrachloride challenge. Insulin-like growth factor 2 (Igf2), a key mitogen that drives growth and liver regeneration, was significantly upregulated in the livers of male, but not female offspring from fathers with inflammation. Taken together, paternal inflammation alters the hepatic Igf2 expression and reprograms growth and liver regeneration in male but not female offspring.

Intergenerational effects of paternal predator cue exposure on behavior, stress reactivity, and neural gene expression

Predation threat impacts prey behavior, physiology, and fitness. Stress-mediated alterations to the paternal epigenome can be transmitted to offspring via the germline, conferring a potential advantage to offspring in predator-rich environments. While intergenerational epigenetic transmission of paternal experience has been demonstrated in mammals, how paternal predator exposure might alter offspring phenotypes across development is unstudied. We exposed male mice to a predator odor (2,4,5-trimethylthiazoline, TMT) or a neutral odor (banana extract) prior to mating and measured offspring behavioral phenotypes throughout development, together with adult stress reactivity and candidate gene expression in the prefrontal cortex, hippocampus, amygdala, and hypothalamus. We predicted that offspring of TMT-exposed males would be less active, would display elevated anxiety-like behaviors, and would have a more efficient stress response relative to controls, phenotypes that should enhance predator avoidance in a high predation risk environment. Unexpectedly, we found that offspring of TMT-exposed males are more active, exhibit less anxiety-like behavior, and have decreased baseline plasma corticosterone relative to controls. Effects of paternal treatment on neural gene expression were limited to the prefrontal cortex, with increased mineralocorticoid receptor expression and a trend towards increased Bdnf expression in offspring of TMT-exposed males. These results suggest that fathers exposed to predation threat produce offspring that are buffered against non-acute stressors and, potentially, better adapted to a predator-dense environment because they avoid trade-offs between predator avoidance and foraging and reproduction. This study provides evidence that ecologically relevant paternal experience can be transmitted through the germline, and can impact offspring phenotypes throughout development.

Sperm pre-fertilization thermal environment shapes offspring phenotype and performance

The sperm pre-fertilization environment has recently been suggested to mediate remarkable transgenerational consequences for offspring phenotype (transgenerational plasticity, TGB), but the adaptive significance of the process has remained unclear. Here, we studied the transgenerational effects of sperm pre-fertilization thermal environment in a cold-adapted salmonid, the European whitefish (Coregonus lavaretus). We used a full-factorial breeding design where the eggs of five females were fertilized with the milt of 10 males that had been pre-incubated at two different temperatures (3.5°C and 6.5°C) for 15 h prior to fertilization. Thermal manipulation did not affect sperm motility, cell size, fertilization success or embryo mortality. However, offspring that were fertilized with 6.5°C-exposed milt were smaller and had poorer swimming performance than their full-siblings that had been fertilized with the 3.5°C-exposed milt. Furthermore, the effect of milt treatment on embryo mortality varied among different females (treatment×female interaction) and male-female combinations (treatment×female×male interaction). Together, these results indicate that sperm pre-fertilization thermal environment shapes offspring phenotype and post-hatching performance and modifies both the magnitude of female (dam) effects and the compatibility of the gametes. Generally, our results suggest that short-term changes in sperm thermal conditions may have negative impact for offspring fitness. Thus, sperm thermal environment may have an important role in determining the adaptation potential of organisms to climate change. Detailed mechanism(s) behind our findings require further attention.

Genetic screens for mutations affecting adult traits and parental-effect genes

Forward genetics remains an important approach for the unbiased identification of factors involved in biological pathways. Forward genetic analysis in the zebrafish has until now largely been restricted to the developmental period from zygotic genome activation through the end of embryogenesis. However, the use of the zebrafish as a model system for the analysis of late larval, juvenile and adult traits, including fertility and maternal and paternal effects, continues to gain momentum. Here, we describe two approaches, based on an F3-extended family and gynogenetic methods, that allow genetic screening for, and recovery of mutations affecting post-embryonic stages, including adult traits, fertility, and parental effects. For each approach, we also describe strategies to maintain, map, and molecularly clone the identified mutations.

The impact of paternal factors on cleavage stage and blastocyst development analyzed by time-lapse imaging-a retrospective observational study

PURPOSE

Various time-lapse studies have postulated embryo selection criteria based on early morphokinetic markers. However, late paternal effects are mostly not visible before embryonic genome activation. The primary objective of this retrospective study was to investigate whether those early morphokinetic algorithms investigated by time-lapse imaging are reliable enough to allow for the accurate selection of those embryos that develop into blastocysts, while of course taking into account the correlation with the type of injected spermatozoa.

METHODS

During a period of 18 months, a total of 461 MII oocytes from 43 couples with severe male factor infertility and previous "external" IVF failures after cleavage-stage embryo transfer (ET) were fertilized by intracytoplasmic morphologically selected sperm injection (IMSI). Thereof, 373 embryos were monitored in a time-lapse incubator until ET on day 5. Blastocyst outcome in combination with three previously postulated MKc (cc2: t3-t2, 5-12 h; t3, 35-40 h; t5, 48-56 h) and the morphology of the selected sperm were analyzed.

RESULTS

A significant increase in the rate of blastocysts (54.0 vs. 36.3 %; P < 0.01) and top blastocysts (25.3 vs. 10.8 %; P < 0.001) was observed in the group of those meeting all three morphokinetic criteria (MKc3). However, MKc3 were only met in 23.3 % of all embryos. Moreover, TBR was influenced by the type of injected spermatozoa. In both groups, TBR decreased dramatically (MKc3, 35.0 vs. 17.0 %; MKc < 3, 14.2 vs. 8.4 %) when class II/III sperm instead of class I were injected.

CONCLUSION

Early morphokinetic parameters might give some predictive information but fail to serve as a feasible selective tool for the prediction of blastocyst development given the influence of the type of spermatozoa injected.