No abstract

Numerous intrauterine changes take place across species during embryo development. Following fertilization in July/August, the European roe deer (Capreolus capreolus) embryo undergoes diapause until embryonic elongation in December/January. Embryonic elongation prior to implantation is a common feature among ungulates. Unlike many other ruminants, the roe deer embryo does not secrete interferon-tau (IFNτ). This provides the unique opportunity to unravel IFNτ-independent signaling pathways associated with maternal recognition of pregnancy (MRP). This study aimed at identifying the cell-type–specific endometrial gene expression changes associated with the MRP at the time of embryo elongation that are independent of IFNτ in roe deer. The messenger RNA (mRNA) expression of genes known to be involved in embryo–maternal communication in cattle, pig, sheep, and mice was analyzed in laser capture microdissected (LMD) endometrial luminal, glandular epithelial, as well as stromal cells. The mRNA transcript abundances of the estrogen (ESR1), progesterone receptor (PGR), and IFNτ-stimulated genes were lower in the luminal epithelium in the presence of an elongated embryo compared to diapause. Retinol Binding Protein-4 (RBP4), a key factor involved in placentation, was more abundant in the luminal epithelium in the presence of an elongated embryo. The progesterone receptor localization was visualized by immunohistochemistry, showing an absence in the luminal epithelium and an overall lower abundance with time and thus prolonged progesterone exposure. Our data show a developmental stage-specific mRNA expression pattern in the luminal epithelium, indicating that these cells sense the presence of an elongated embryo in an IFNτ-independent manner.

No abstract

No abstract

The early developing embryo faces a continuously changing microenvironment to supports its growth. In the European roe deer, this environment accompanies embryonic diapause, a period of up to 4 months in which fertilization and subsequent implantation are decoupled. Diapause is characterised by a deceleration of embryonic growth. In most ruminants such as cattle and sheep, interferon tau (IFNt) plays a major role in maternal recognition of pregnancy. Uniquely to ruminants, the roe deer embryo does not secrete IFNt. The roe deer was used as a model species to gain insights into the changing uterine environment devoid of IFNt that supports prolonged decelerated embryo development, resumption of developmental velocity, and subsequent implantation. Uterine fluid samples from 188 female does were collected during regular huntings between September and January, and 4 developmental stages-blastocysts at early, mid, and late diapause and elongated embryos (16, 57, 97, and 18 does per developmental stage, respectively)-were defined. The developmental stages were assigned based on morphological characteristics of the embryo and the embryonic genomic DNA content. For the analysis of amino acids (AA), all 188 uterine fluid samples were subjected to targeted liquid chromatography-tandem mass spectrometry. Almost all AA increased over the course of embryo development. Although most AA showed developmental stage-specific concentration peaks, serine, glycine, alanine, glutamate, and glutamine were most abundantly present irrespective of the developmental progression. For the analysis of the protein abundances in the uterine fluid in a selected subset of samples (n=5 per developmental stage), holistic liquid chromatography-tandem mass spectrometry identified and quantified a total of 819 proteins with a false discovery rate of <1%. Comparison between the developmental stages revealed 106 differentially abundant proteins. Most changes in protein abundance that occurred related to embryo elongation. Interestingly, 713 proteins remained stable during embryo development, indicating that these proteins may contribute to prolonged embryo survival during embryonic diapause. The differentially abundant proteins were clustered with DAVID Bioinformatics Resources 6.8 (https://david.ncifcrf.gov/). The most enriched clusters were cell-cell adhesion, biosynthesis of AA and carbon metabolism, microtubule, structural molecule activity, and chaperone binding. The ongoing detailed identification of stably abundant proteins will advance our basic understanding of the embryos’ needs for sustained survival during prolonged decelerated development. In addition, a comparison with the protein abundances around the time of maternal recognition of pregnancy in other species could advance our knowledge on conserved proteins that support embryo development and establishment of pregnancy in mammals. Our findings may contribute to defining optimal in vitro embryo culture conditions in a species-independent manner and potentially identify factors capable of halting embryo development.