Identification of novel structures in term human placenta using serial block face scanning electron microscopy

Abstract

The placenta is a vital organ for the normal development and growth of the fetus. Inadequate placental function can result in poor fetal growth, which is associated with diseases in adult life. Understanding the structure and function of the normal placenta will enhance our understanding of the mechanisms underlying the placental dysfunction. Investigating the structure of the different cell types, the relationships between them and relating their structure to their function will result in a better understanding of the structures underlying placental function. Previous work on placental structure has primarily been based on 2D sections, however new 3D approaches are now available and this thesis has sought to use these to enhance our understanding of placental structure at different scales.

To investigate the placental structure new 3D imaging techniques have been utilised in this project. Serial block face scanning electron microscopy (SBFSEM) along with transmission electron microscopy and confocal laser scanning microscopy have been used to visualize in more depth the different cell types in the human placenta and also reconstruct cellular structures in 3D. A stereology approach was performed to allow quantifiable analysis of the different cellular structures.

SBFSEM revealed novel structures in the placenta that could not be observed in 2D. SBFSEM demonstrated a fetal erythrocyte protruding through syncytiotrophoblast, enabled the 3D reconstruction of a placental fibroblast and the interactions of fibroblast processes with other fibroblasts as a fibroblast network and in contact with giant extracellular vesicles. SBFSEM also revealed the existence of inter-endothelial protrusions (IEPs) found inside the endothelial cells in terminal villi of term normal placenta.

The existence of fibroblast networks, the interactions of fibroblast processes with giant extracellular vesicles and the identification of IEPs between endothelial cells demonstrate how 3D approaches allows us to better understand placental structure and the relationships between different cell types. Segmentation of thousands of slices generated by SBFSEM technique is a very time-consuming process and thus the development of automated segmenting techniques are necessary to reduce the amount of time and effort in segmentation.

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Identifiers

ORCID for Jane Cleal: orcid.org/0000-0001-7978-4327

ORCID for Rohan Lewis: orcid.org/0000-0003-4044-9104

ORCID for Bram Sengers: orcid.org/0000-0001-5859-6984

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