Cell specification and functional interactions in the pig blastocyst inferred from single cell transcriptomics
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Abstract
The early embryonic development of the pig comprises a long in utero pre- and peri-implantation development, which dramatically differs from mouse and human. During this pro-tracted peri-implantation period, an intimate dialogue between the embryo and the uterus is established through a complex series of paracrine signals. It leads to concomitant drastic changes in the embryonic morphology and uterine receptivity to implantation. From day 7 after fertilization, the spherical blastocyst elongates as ovoid, tubular and filamentous wich transforms from a 0.5-1 mm diameter sphere to a 1000 mm long filamentous blastocyst at day 16. At the same time, the inner cell mass moves up to the trophoblast as the Rauber’s layer disappears and evolves as an embryonic disc that is directly exposed to molecules present in the uterine fluids. These drastic changes occurring before implantation are driven and coordinated by interactions between embryonic cells and maternal tissues.
To better understand the biology of pig embryos before implantation, we generated a large dataset of single-cell RNAseq at different embryonic stages (early and hatched blastocyst, spheroid and ovoid conceptus) and proteomic datasets from corresponding uterine fluids. These data were cleaned, filtered and represent a total of 34,888 cells. We first characterised the embryonic and extra-embryonic cell populations and their evolution, and identified population-specific markers of the three main populations (epiblast, trophectoderm and hypoblast). Our analysis also confirmed known functions and predicted new biological functions associated with these cell populations.We then inferred gene regulatory networks working on modules of gene regulation (regulon) and selected those that were specifically active in each embryonic population. We confirmed the relevance of the identified regulons by a meta-analysis of two other scRNAseq datasets (porcine and human preimplantation embryos). We then linked these regulons to signalling pathways and biological processes. Our results confirm the molecular specificity and functionality of the three main cell populations and identify novel stage-specific subpopulations. In particular, we discovered two previously unknown subpopulations of the trophectoderm, one characterised by the expression of LRP2, which could represent a subpopulation of progenitor cells, and the other, expressing many pro-apoptotic markers, which could correspond to the cells of the Rauber’s layer. We also provide new insights into the biology of these populations, their reciprocal functional interactions and the molecular dialogue established with the maternal uterine environment.
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conserved role of IL1B genes between pig and human/monkey
Since you didn't include mice here, am I correct to assume that this is something that is NOT conserved in mice. And therefore an advantage to using pig as a model for human biology?
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Figure 1A
This was super helpful. Thank you!
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earch to improve the derivation, stability and survival of porcine ESCs.
Maybe this is leftover from a previous version?
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Proteomic datasets were also generated from the uterine fluids of the sows used for embryo production
As an outsider to this field, it would be helpful for me to better understand the rationale for including uterine fluids. It seems important, and I want to make sure I understand why!
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The early stage shows a protein intensity profile with functions associated with cell metabolism, such as those involved in glycolysis GAPDH, ENO1, AKR1A1, PKM, IDH1 (Figure 6B) [53]–[57] pyruvate mechanism LDHA/B (Figure 6B) [58] and proteins with pleiotropic functions such as proteins of 14-3-3 and YWHAQ/Z/E families, recently identified as key players during the maternal-to-zygotic transition in pigs (Figure 6B) [59].
Would be curious to know your interpretation of this result. Do you think these proteins are being secreted by the uterine lining or the embryo itself? i.e. in which direction is communication happening?
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whose transcriptional profiles are very different from the later lineages
Curious if these transcriptional profiles provided any insights for you on other proxies you could measure in the future that may help you differentiate between cell types and stages? i.e. key metabolites/hormones that could be assayed for instead of sequencing?
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