Novel aspects of endometrial function: a biological sensor of embryo quality and driver of pregnancy success

Successful pregnancy depends on complex biological processes that are regulated temporally and spatially throughout gestation. The molecular basis of these processes have been examined in relation to gamete quality, early blastocyst development and placental function, and data have been generated showing perturbations of these developmental stages by environmental insults or embryo biotechnologies. The developmental period falling between the entry of the blastocyst into the uterine cavity to implantation has also been examined in terms of the biological function of the endometrium. Indeed several mechanisms underlying uterine receptivity, controlled by maternal factors, and the maternal recognition of pregnancy, requiring conceptus-produced signals, have been clarified. Nevertheless, recent data based on experimental perturbations have unveiled unexpected biological properties of the endometrium (sensor/driver) that make this tissue a dynamic and reactive entity. Persistent or transient modifications in organisation and functionality of the endometrium can dramatically affect pre-implantation embryo trajectory through epigenetic alterations with lasting consequences on later stages of pregnancy, including placentation, fetal development, pregnancy outcome and post-natal health. Developing diagnostic and prognostic tools based on endometrial factors may enable the assessment of maternal reproductive capacity and/or the developmental potential of the embryo, particularly when assisted reproductive technologies are applied.

Transcriptome profile of early mammalian embryos in response to culture environment

Early embryonic development, the period from maturation until blastocyst formation, is one of the most critical periods of mammalian development involves various morphological, cellular, and biochemical changes related to genomic activity. During the post-fertilization period, several major developmental events occur in the embryo which are regulating by a harmonized expression of genes and strongly influenced by culture conditions. The products of these genes are involved in various biological processes including metabolism, growth factor/cytokine signaling, stress adaptation, transcription and translation, epigenetic regulation of transcription, apoptosis, compaction and blastocyst formation. Post-fertilization culture environment is known to be the most important factor determining the quality of the resulting embryos as indicated in terms of cryo-tolerance and relative abundance of transcripts. However, the exact effect of culture conditions on gene expression and subsequent influences on molecular pathways controlling early development is still unknown. A number of culture environmental factors can influence the gene expression of produced embryos such as media composition, serum supplementation, number of embryos present in the culture drop and gas atmosphere. During the last ten years several studies were concerned with differences in the transcriptome profile of embryos produced under different environmental conditions and its subsequent influence on embryo developmental competence. From these studies, several genes have been determined as candidate genes controlling preimplantation embryo development and affecting its quality. Here we will discuss results of different experiments investigated the effect of different culture conditions on the transcriptome profile of bovine blastocyst. These experiments identified molecular mechanisms and pathways that influenced by culture conditions and this will enable to launch strategies to modify culture conditions to enhance the development of competent blastocyst.

Transcriptional response of the bovine endometrium and embryo to endometrial polymorphonuclear neutrophil infiltration as an indicator of subclinical inflammation of the uterine environment

The aim of the present study was to analyse the effect of subclinical endometritis on endometrial and embryonic gene expression. A total of 49 cows at either Day 0 or Day 7 of the oestrous cycle (62–83 days post partum) following superovulation were classified as having subclinical endometritis (SE-0, SE-7) or a healthy endometrium (HE-0, HE-7) on the basis of endometrial cytological evaluation. Endometrial samples and associated embryos were subjected to global transcriptome analysis using the Bovine GeneChip (Affymetrix, Santa Clara, CA, USA) and aberrant transcript profiles were observed in SE-0 and SE-7 cows. At Day 0, 10 transcripts were found to be differentially expressed in endometrial samples. Specifically, the PDZK1, PXDN, DDHD2, GPLD1 and SULT1B1 genes were downregulated, whereas the PKIB, LOC534256, BT29392, LYZ and S100A14 genes were upregulated in SE-0 cows. Similarly, 11 transcripts were found to be differentially regulated on Day 7. Of these, GNPTG, BOLA-DQA5, CHD2, LOC541226, VCAM1 and ARHGEF2 were found to be downregulated, whereas PSTPIP2, BT236441 and MGC166084 were upregulated in SE-7 cows. Accordingly, endometrial health status affected the number of flushed, transferable embryos. In all, 20 genes were differentially regulated in blastocysts derived from HE-7 and SE-7 cows. Of these, GZMK, TCEAL4, MYL7, ADD3 and THEM50B were upregulated, whereas NUDCD2, MYO1E, BZW1, EHD4 and GZMB were downregulated. In conclusion, endometrial polymorphonuclear neutrophil infiltration as an indicator of subclinical endometritis is associated with changes in endometrial gene expression patterns, including genes involved in cell adhesion and immune modulation. Consequently, subclinical endometritis affects gene expression in embryos, including the expression of genes related to membrane stability, the cell cycle and apoptosis.