Decoding the Secrets of Human Tissue: A Comprehensive Guide

Image showing a cross-section of a retinal organoid, where diverse tissue structures are highlighted in varying colors. Credit: Wahle et al. Nature Biotechnology 2023

The search is on to identify the specific cells found in different human tissues and their exact locations. We aim to understand the genes that become active within these cells and the proteins identifiable inside them. A specialized guide is being developed to provide detailed answers to these questions, with a particular emphasis on illuminating how various tissues form during embryonic development and identifying the root causes of diseases.

The researchers involved in this project strive to map not only tissues derived directly from humans but also structures known as organoids. These lab-grown three-dimensional tissue clusters mirror the development of human organs, albeit on a smaller scale.

Barbara Treutlein, Professor of Quantitative Developmental Biology at the Department of Biosystems Science and Engineering at ETH Zurich in Basel, explains that “organoids give us the opportunity to manipulate their growth and apply various active substances to them. This allows us to learn more about both healthy tissues and diseases.”

To assist in the creation of this guide, Treutlein and her team, alongside researchers from the Universities of Zurich and Basel, have designed a method to gather and collate extensive information about organoids and their development. They applied this technique to human retina organoids, which were derived from stem cells.

Multiple Proteins Made Visible Simultaneously

A key tool in this approach was the 4i technology, known as iterative indirect immunofluorescence imaging. This innovative imaging technique, developed by Lucas Pelkmans, a professor at the University of Zurich, allows for the visualization of several dozen proteins in a thin tissue section at high resolution using fluorescence microscopy. The researchers have now applied this technology to organoids for the first time.

Fluorescence microscopy is commonly used by researchers to emphasize three proteins in a tissue, each with a unique fluorescent dye. Technical limitations usually prevent the staining of more than five proteins simultaneously. However, the 4i technology uses three dyes, which are then washed off after measurement, allowing for the staining of three new proteins. A robot performed this procedure 18 times over 18 days. Finally, a computer compiles the individual images into a single microscopic image, rendering 53 different proteins visible. This information helps identify the functions of individual cell types making up the retina, such as rods, cones, and ganglion cells.

The team also supplemented this visual data of retinal proteins with information on the genes expressed in the individual cells.

Detailed Spatiotemporal Analysis

The scientists carried out these analyses on organoids of different ages and thus at varying developmental stages. This allowed them to create a sequence of images and genetic data that narrates the entire 39-week development of retinal organoids. “This sequence enables us to illustrate how the organoid tissue progressively forms, identifying which cell types proliferate and when, and locating the synapses. These processes mirror those of retinal formation during embryonic development,” remarks Gray Camp, a professor at the University of Basel and a senior author of the study.

The research team has made their image data and additional findings on retinal development publicly available on the EyeSee4is website.

Exploring Further Tissue Types

Up to now, the team’s focus has been on the development of a healthy retina, but they plan to intentionally disturb the development of retinal organoids in the future using drugs or genetic alterations. “This approach will provide new insights into conditions such as retinitis pigmentosa, a genetic disorder causing the gradual degeneration and eventual blindness due to the loss of the retina’s light-sensitive receptors,” says Camp. The team aims to determine when this process begins and how it can be halted.

Alongside this, Treutlein and her colleagues intend to apply their in-depth mapping method to other tissue types, including different areas of the human brain and various tumor tissues. Gradually, this work will contribute to the development of a guide offering information on the growth of human organoids and tissues.

Reference: “Multimodal spatiotemporal phenotyping of human retinal organoid development” by Philipp Wahle, Giovanna Brancati, Christoph Harmel, Zhisong He, Gabriele Gut, Jacobo Sarabia del Castillo, Aline Xavier da Silveira dos Santos, Qianhui Yu, Pascal Noser, Jonas Simon Fleck, Bruno Gjeta, Dinko Pavlinić, Simone Picelli, Max Hess, Gregor W. Schmidt, Tom T. A. Lummen, Yanyan Hou, Patricia Galliker, David Goldblum, Marton Balogh, Cameron S. Cowan, Hendrik P. N. Scholl, Botond Roska, Magdalena Renner, Lucas Pelkmans, Barbara Treutlein and J. Gray Camp, 8 May 2023, Nature Biotechnology.
DOI: 10.1038/s41587-023-01747-2

Frequently Asked Questions (FAQs) about Organoid Research

More about Organoid Research

• Nature Biotechnology: “Multimodal spatiotemporal phenotyping of human retinal organoid development”
• ETH Zurich: Department of Biosystems Science and Engineering
• University of Zurich
• University of Basel
• [EyeSee4is website](insert website URL when available)