title: Autocrine embryotropins revisited: how do embryos communicate with each other in vitro when cultured in groups?
abstract: In the absence of the maternal genital tract, preimplantation embryos can develop in vitro in culture medium where all communication with the oviduct or uterus is absent. In several mammalian species, it has been observed that embryos cultured in groups thrive better than those cultured singly. Here we argue that group-cultured embryos are able to promote their own development in vitro by the production of autocrine embryotropins that putatively serve as a communication tool. The concept of effective communication implies an origin, a signalling agent, and finally a recipient that is able to decode the message. We illustrate this concept by demonstrating that preimplantation embryos are able to secrete autocrine factors in several ways, including active secretion, passive outflow, or as messengers bound to a molecular vehicle or transported within extracellular vesicles. Likewise, we broaden the traditional view that inter-embryo communication is dictated mainly by growth factors, by discussing a wide range of other biochemical messengers including proteins, lipids, neurotransmitters, saccharides, and microRNAs, all of which can be exchanged among embryos cultured in a group. Finally, we describe how different classes of messenger molecules are decoded by the embryo and influence embryo development by triggering different pathways. When autocrine embryotropins such as insulin-like growth factor-I (IGF-I) or platelet activating factor (PAF) bind to their appropriate receptor, the phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) pathway will be activated which is important for embryo survival. On the other hand, the mitogen-activated protein kinase (MAPK) pathway is activated when compounds such as hyaluronic acid and serotonin bind to their respective receptors, thereby acting as growth factors. By activating the peroxisome-proliferator-activated receptor family (PPAR) pathway, lipophilic autocrine factors such as prostaglandins or fatty acids have both survival and anti-apoptotic functions. In conclusion, considering different types of messenger molecules simultaneously will be crucial to understanding more comprehensively how embryos communicate with each other in group-culture systems. This approach will assist in the development of novel media for single-embryo culture.
authors.affiliation: Department of Reproduction, Obstetrics, and Herd Health, Faculty of Veterinary Medicine, Ghent University, B-9820, Merelbeke, Belgium.
authors.forename: Eline
authors.initials: E
authors.lastname: Wydooghe
authors.affiliation: Animal Sciences Unit, Institute for Agricultural and Fisheries Research (ILVO), B-9090, Melle, Belgium.
authors.forename: Leen
authors.initials: L
authors.lastname: Vandaele
authors.affiliation: Department of Reproduction, Obstetrics, and Herd Health, Faculty of Veterinary Medicine, Ghent University, B-9820, Merelbeke, Belgium.
authors.forename: Sonia
authors.initials: S
authors.lastname: Heras
authors.affiliation: Department of Reproductive Medicine, University Hospital, Ghent University, B-9000, Ghent, Belgium.
authors.forename: Petra
authors.initials: P
authors.lastname: De Sutter
authors.affiliation: Laboratory for Pharmaceutical Biotechnology, Ghent University, B-9000, Ghent, Belgium.
authors.forename: Dieter
authors.initials: D
authors.lastname: Deforce
authors.affiliation: Laboratory of Animal Genetics, Faculty of Veterinary Medicine, Ghent University, B-9820, Merelbeke, Belgium.
authors.forename: Luc
authors.initials: L
authors.lastname: Peelman
authors.affiliation: Department of Reproduction, Obstetrics, and Herd Health, Faculty of Veterinary Medicine, Ghent University, B-9820, Merelbeke, Belgium.
authors.forename: Catharina
authors.initials: C
authors.lastname: De Schauwer
authors.affiliation: Department of Reproduction, Obstetrics, and Herd Health, Faculty of Veterinary Medicine, Ghent University, B-9820, Merelbeke, Belgium.
authors.forename: Ann
authors.initials: A
authors.lastname: Van Soom
mesh_terms: D000818:Animals; D001755:Blastocyst / Q000201:enzymology / Q000378:metabolism / Q000502:physiology*; D002450:Cell Communication / Q000502:physiology*; D003470:Culture Media; D004622:Embryo, Mammalian; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism
chemical_list: D003470:Culture Media; D019869:Phosphatidylinositol 3-Kinases
keywords: autocrine factors; exosome; group culture; growth factors; in vitro fertilization; inter-embryo communication; paracrine factors; preimplantation embryo; survival factors