Placental alterations in structure and function in intra-uterine growth-retarded horses

Could assisted reproductive techniques affect equine fetal membranes and neonatal outcome?

Embryo transfer (ET) and intracytoplasmic sperm injection (ICSI) are widely used in equine species, but their effects on fetal adnexa and neonates have not been investigated yet. The aim of this study was to retrospectively evaluate whether pregnancies obtained by ET or ICSI could be associated with the presence of macroscopic alterations of fetal membranes (FM) and umbilical cord (UC) and if the use of these techniques could influence neonatal outcome. Sixty-six light breed mares hospitalized at the Veterinary Teaching Hospital, University of Bologna, for attending delivery were included in the study. Mares were divided into Artificial Insemination (AI; 32/66 mares, 48 %), Embryo Transfer (ET; 12/66 mares, 18.2 %) and Intracytoplasmic Sperm Injection (ICSI; 22/66 mares, 33 %) groups. All the medical reports of mares and their foals were reviewed and data about mare, pregnancy, foaling, fetal membranes, umbilical cord and foal were recorded. The occurrence of dystocia resulted statistically different between AI group and ICSI group (p = 0.0066), and between AI group and ET group (p = 0.044). Macroscopic examination of FM revealed alterations in 30/66 mares (46 %): 8/32 in AI (25 %), 7/12 in ET (58 %) and 15/22 in ICSI (68 %) with significant lower incidence in AI compared to ET (p = 0.04) and ICSI (p = 0.002) groups. Alterations reported were chorionic villi hypoplasia, chorioallantois edema, allantois cysts, necrotic areas and greenish-grey concretions. Total length of UC resulted significantly shorter in ICSI group (49 ± 9 cm; p < 0.03) compared to AI (60 ± 17 cm) and ET (59 ± 15 cm). However, there were no differences in the incidence of foals' diseases at birth and in foals' survival among groups (p > 0.05). The results demonstrate that transfer of in vivo or in vitro produced embryos may lead to alterations of placental development, as observed in other species, without being associated with a higher incidence of neonatal morbidity and mortality. Further studies about trophoblast development, FM histological evaluation, and placental gene expression should be carried out to clarify the mechanisms underlying the placental alterations.

Resiliency of equid H19 imprint to somatic cell reprogramming by oocyte nuclear transfer and genetically induced pluripotency†

Cell reprogramming by somatic cell nuclear transfer and in induced pluripotent stem cells is associated with epigenetic modifications that are often incompatible with embryonic development and differentiation. For instance, aberrant DNA methylation patterns of the differentially methylated region and biallelic expression of H19-/IGF2-imprinted gene locus have been associated with abnormal growth of fetuses and placenta in several mammalian species. However, cloned horses are born with normal sizes and with no apparent placental anomalies, suggesting that H19/IGF2 imprinting may be epigenetically stable after reprogramming in this species. In light of this, we aimed at characterizing the equid H19 gene to determine whether imprinting is altered in somatic cell nuclear transfer (SCNT)-derived conceptuses and induced pluripotent stem cell (iPSC) lines using the mule hybrid model. A CpG-rich region containing five CTCF binding sites was identified upstream of the equine H19 gene and analyzed by bisulfite sequencing. Coupled with parent-specific and global H19 transcript analysis, we found that the imprinted H19 remains monoallelic and that on average the methylation levels of both parental differentially methylated regions in embryonic and extra-embryonic SCNT tissues and iPSC lines remained unaltered after reprogramming. Together, these results show that, compared to other species, equid somatic cells are more resilient to epigenetic alterations to the H19-imprinted locus during SCNT and iPSC reprogramming.

Fetal morphological features and abnormalities associated with equine early pregnancy loss

BACKGROUND

Early pregnancy loss (EPL) occurs in approximately 8% of equine pregnancies, although the aetiology is mostly unknown and embryonic/fetal morphological abnormalities associated with EPL are not defined.

OBJECTIVES

To compare the morphology of EPL to clinically normal embryos/fetuses and previously described embryonic/fetal developmental milestones. To identify morphological abnormalities associated with equine EPL.

STUDY DESIGN

Observational case-control study.

METHODS

Embryos/fetuses were obtained from clinically normal Thoroughbred and pony pregnancies (n = 11) and following EPL from Thoroughbred mares (n = 27). The crown-rump length (CRL) of embryos/fetuses was measured and macroscopic morphology and developmental age were determined independently by three blinded examiners. Sagittal sections of EPL (n = 13) and control (n = 6) embryos/fetuses were assessed microscopically. Fisher's exact test was used to determine significance (P < .05) and correlations were expressed by Pearson coefficient.

RESULTS

Age and CRL were strongly positively correlated in clinically normal Thoroughbred and reference (n = 15, R = .9 (95% CI: 0.8-1.0), R²  = .9, P < .0001) but not EPL embryos/fetuses (n = 19, R = .1 (95% CI: -0.4 to 0.5), R²  = .01, P = .75). Relative to controls, the CRL of EPL embryos/fetuses was smaller, with evidence of intrauterine growth retardation (IUGR) in 3/8 fetuses assessed. In 9/13 EPL embryos/fetuses, nonspecific neural tissue alterations were identified including disruption of developing pros-, mes- and rhombencephalon and the presence of haemosiderin, indicating premortem haemorrhage. Failed neural tube closure was identified in 1/13 EPL embryos/fetuses. Subcutaneous haemorrhage was present in 14/27 EPL embryos/fetuses.

MAIN LIMITATIONS

Autolysis significantly affected 15/27 EPL embryos/fetuses, excluding them from complete assessment. The IUGR reference cut-off values were based on a small number of controls.

CONCLUSIONS

Morphological features associated with equine EPL were a mismatch between embryonic/fetal size and age, and alterations of the developing neural tissue and localised subcutaneous haemorrhage. Failed neural tube closure was confirmed as a rare specific abnormality.

Physiological development of the equine fetus during late gestation

In many species, the pattern of growth and physiological development in utero has an important role in determining not only neonatal viability but also adult phenotype and disease susceptibility. Changes in fetal development induced by a range of environmental factors including maternal nutrition, disease, placental insufficiency and social stresses have all been shown to induce adult cardiovascular and metabolic dysfunction that often lead to ill health in later life. Compared to other precocious animals, much less is known about the physiological development of the fetal horse or the longer-term impacts on its phenotype of altered development in early life because of its inaccessibility in utero, large size and long lifespan. This review summaries the available data on the normal metabolic, cardiovascular and endocrine development of the fetal horse during the second half of gestation. It also examines the responsiveness of these physiological systems to stresses such as hypoglycaemia and hypotension during late gestation. Particular emphasis is placed on the role of the equine placenta and fetal endocrine glands in mediating the changes in fetal development seen towards term and in response to nutritional and other environmental cues. The final part of the review presents the evidence that the early life environment of the horse can alter its subsequent metabolic, cardiovascular and endocrine phenotype as well as its postnatal growth and bone development. It also highlights the immediate neonatal environment as a key window of susceptibility for programming of equine phenotype. Although further studies are needed to identify the cellular and molecular mechanisms involved, developmental programming of physiological phenotype is likely to have important implications for the health and potential athletic performance of horses, particularly if born with abnormal bodyweight, premature or dysmature characteristics or produced by assisted reproductive technologies, indicative of an altered early life environment.