Endometrial receptivity in cattle: the mutual reprogramming paradigm.

Prior to implantation in cattle, the mucous medium contained in the uterine lumen serves as a working interface for molecular exchange and signaling between the lining endometrium and the embryo. The composition of this luminal fluid changes temporally according to the secretory and reabsorptive activities of the uterus and the embryo, which are under complex regulation. Via this interface, both the embryo and the endometrium reprogram each other's functions to support pregnancy continuation beyond the pre-implantation period. More specifically, the embryo receives elongation signals and the uterus receives anti-luteolytic stimuli. Here, characteristics of the luminal compartment as well as the regulation of its composition to determine the pregnancy outcome will be discussed.

Endometrial receptivity in cattle: the mutual reprogramming paradigm

Prior to implantation in cattle, the mucous medium contained in the uterine lumen serves as a working interface for molecular exchange and signaling between the lining endometrium and the embryo. The composition of this luminal fluid changes temporally according to the secretory and reabsorptive activities of the uterus and the embryo, which are under complex regulation. Via this interface, both the embryo and the endometrium reprogram each other's functions to support pregnancy continuation beyond the pre-implantation period. More specifically, the embryo receives elongation signals and the uterus receives anti-luteolytic stimuli. Here, characteristics of the luminal compartment as well as the regulation of its composition to determine the pregnancy outcome will be discussed.(AU)

The pre-hatching bovine embryo transforms the uterine luminal metabolite composition in vivo.

In cattle, conceptus development after elongation relies on well-characterized, paracrine interactions with the hosting maternal reproductive tract. However, it was unrecognized previously that the pre-hatching, pre-implantation bovine embryo also engages in biochemical signalling with the maternal uterus. Our recent work showed that the embryo modified the endometrial transcriptome in vivo. Here, we hypothesized that the embryo modulates the biochemical composition of the uterine luminal fluid (ULF) in the most cranial portion of the uterine horn ipsilateral to the corpus luteum. Endometrial samples and ULF were collected post-mortem from sham-inseminated cows and from cows inseminated and detected pregnant 7 days after oestrus. We used quantitative mass spectrometry to demonstrate that the pre-hatching embryo changes ULF composition in vivo. Embryo-induced modulation included an increase in concentrations of lipoxygenase-derived metabolites [12(S)-HETE, 15(S)-HETE] and a decrease in the concentrations of amino acids (glycine), biogenic amines (sarcosine), acylcarnitines and phospholipids. The changed composition of the ULF could be due to secretion or depletion of specific molecules, executed by either the embryo or the endometrium, but initiated by signals coming from the embryo. This study provides the basis for further understanding embryo-initiated modulation of the uterine milieu. Early embryonic signalling may be necessary to guarantee optimal development and successful establishment of pregnancy in cattle.

Negative energy balance and metabolic stress in relation to oocyte and embryo quality: an update on possible pathways reducing fertility in dairy cows

A negative energy balance in metabolically compromised high producing dairy cows has been shown to influence oocyte and embryo quality. However, the possible involved pathways needed more attention to better understandspecific deleterious effects. Oocyte maturation is the first process to be scrutinized. Because many possible metabolic factors might directly impact oocyte quality, systematic in vitroapproaches were used to investigate the effects of oocyte maturation under elevated NEFA concentrations. Blastocysts originating from NEFA-exposed oocytes showed a lower cell number, an increased apoptotic cell index, signs of glucose intolerance, sensitive to oxidative stress and mitochondrial dysfunction. Defining these embryos’ transcriptome and epigenome signatures revealed changes in DNA methylation patterns. Long-term exposure of developing murine follicles to elevated NEFA concentrations showed to impair oocyte developmental competence even more. While little is known on how the oviductal micro-environment can change as a consequence of a negative energy balance, a validated in vitrobovine oviduct model offered some valuable insights on how NEFAs disturb oviductal cell physiology. NEFA exposure reduces cell proliferation, cell migration, sperm binding capacity and monolayer integrity. In addition, oviductal cells seem to play an active role in regulating luminal NEFA-concentrations through increased permeability, intracellular lipid accumulation and fatty acid metabolism. This might favour early embryo development. The establishment of a successful pregnancy largely depends on the ability of the embryo to interact with a properly prepared endometrium.

A diet enriched in linoleic acid compromises the cryotolerance of embryos from superovulated beef heifers.

Dietary rumen-protected fat rich in linoleic acid may affect the superovulatory response and embryo yield; however, its effects on in vivo embryo cryotolerance are unknown in zebu cattle. The present study evaluated the production and cryotolerance after freezing or vitrification of embryos from Nelore heifers supplemented with rumen-protected polyunsaturated fatty acids (PUFA). Forty heifers kept in pasture were randomly distributed into two groups according to the type of feed supplement (F, supplement with rumen-protected PUFA, predominantly linoleic; C, control fat-free supplement with additional corn). Supplements were formulated to be isocaloric and isonitrogenous. Each heifer underwent both treatments in a crossover design with 70 days between replicates. After 50 days feeding, heifers were superovulated. Embryos were evaluated morphologically and vitrified or frozen. After thawing or warming, embryo development was evaluated in vitro. There was no difference between the F and C groups (P>0.10) in terms of embryo production. Regardless of the cryopreservation method used, Group C embryos had a greater hatching rate after 72h in vitro culture than Group F embryos (44.3±4.2% (n=148) vs 30.9±4.0% (n=137), respectively; P=0.04). Moreover, vitrified and frozen embryos had similar hatching rates (P>0.10). In conclusion, dietary rumen-protected PUFA rich in linoleic acid did not improve embryo production and compromised the cryotolerance of conventionally frozen or vitrified embryos from Nelore heifers.