Researchers have identified the earliest display of an innate immune response found in vertebrate animals to date.
Embryogenesis
Early embryogenesis is prone to cellular errors that are induced by intrinsic and extrinsic stress factors. This subsequently leads to sporadic cell death of progenitor stem cells. It is also believed to be a major cause of early developmental failures in human pre-implantation development. The detection and removal of cell corpses requires a clearance mechanism similar to that done by professional phagocytic cells in adult tissues. The existence of such a mechanism in the early blastula and gastrula stages of vertebrate development is still not fully understood.
Immune response
In this study, published in Nature, researchers used high resolution time-lapse imaging technology to monitor zebrafish and mouse embryos.
They found that the surface epithelium (first tissue formed during vertebrate development) of zebrafish and mouse embryos performed efficient phagocytic clearance of apoptotic cells through phosphatidylserine-mediated target recognition. This is the first time this biological process – epithelial phagocytosis – has been shown to clear cellular errors in newly formed vertebrate embryos.
This process is specifically facilitated by two types of Rac1-dependent basal epithelial protrusions. The first involves phagocytic cups which mediate apoptotic target uptake. The second type is a previously undescribed type of fast and extended actin-based protrusion – ‘epithelial arms’. This promotes the rapid dispersal of apoptotic targets.
Summary
Overall, these findings show that epithelial tissue clearance facilitates error correction. This process specifically indicates the presence of an innate immune function in the earliest stages of embryonic development. This work may aid future efforts to understand why some embryos fail to form. Consequently, this may lead to new clinical efforts in treating infertility or early miscarriages.
Dr. Verena Ruprecht, senior author, stated:
“Here we propose a new evolutionarily conserved function for epithelia as efficient scavengers of dying cells in the earliest stages of vertebrate embryogenesis.
Our work may have important clinical applications by one day leading to improved screening methods and embryo quality assessment standards used in fertility clinics.”
Image by Weslley Carvalho de Souza Weslleycs97 from Pixabay
