3D rendering of the cellular assembly of the tactile organs of the fruit fly Drosophila using SBF-SEM

3D Morphology of Tactile Sensory Organs with Volume Electron Microscopy

byZEISS Microscopy 18 December 2023 4 min read

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3D Morphology of Tactile Sensory Organs with Volume Electron Microscopy

SBF-SEM provides insights into a new type of specialized epidermal cell involved in touch sensing in Drosophila.

Touch is an essential sense, allowing us to gather information about the world around us. The touch sensation is evoked through direct contact with our skin by cutaneous mechanosensory organs, which convert this stimulus into neuronal impulses. However, little is known about the development of these tactile organs.

Dr. Federica Mangione is a senior postdoctoral fellow in the Apoptosis and Proliferation Control Laboratory headed by Dr. Nicolas Tapon at the Francis Crick Institute, United Kingdom. In her independent line of research, she works to understand the sensory function of the epidermis and the cellular basis of touch. She studies how tactile sensory organs, such as the hairs on our skin, form during development to allow touch sensation. Dr. Mangione recently published a paper describing a new type of specialized epidermal cells, called F-cells, involved in touch sensing in Drosophila. In her work, she combined diverse microscopy methodologies to characterize the tactile bristles within the epidermis, including high resolution morphology studies with volume electron microscopy using SBF-SEM with ZEISS Sigma FE-SEM in collaboration with the Electron Microscopy Platform at the Francis Crick Institute.

My aim was to fully access the structure of these tactile organs in 3D through differentiation while maintaining their native context. We achieved this ambitious goal by imaging sequential stages of differentiation using SBF-SEM and carefully segmenting the cells of these mini-organs.

Dr. Federica Mangione
Senior Postdoctoral Fellow, Apoptosis and Proliferation Control Laboratory, Francis Crick Institute, United Kingdom

3D Volume Electron Microscopy of Developing Tactile Bristles

SBF-SEM Data Acquired with ZEISS Sigma FE-SEM

Aligned SBF-SEM dataset and 2D segmentation of the differentiating tactile bristle and F-Cell. Raw data is on the left and the segmented cells are shown on the right: F-Cell (magenta), socket cell (green), shaft cell (light blue), sheath cell (orange), and neuron (yellow). Data acquired with ZEISS Sigma FE-SEM.

SBF-SEM Acquisition and Segmentation

To characterize the morphology of the F-Cell and its interaction with the tactile organ at higher resolution, Dr. Mangione created 3D renderings of the bristle structure using serial block face scanning electron microscopy (SBF-SEM) at different timepoints during differentiation.

SBF-SEM creates a 3D ultra resolution image by imaging sections from a sample block using an ultramicrotome inside the SEM chamber. Here is one example of the 2D images of a Drosophila bristle and F-Cell with the raw data on the left and the segmented cells on the right.

3D morphology of the differentiating tactile bristle and associated F-Cell. F-Cell (magenta), socket cell (green), shaft cell (light blue), sheath cell (orange), and neuron (yellow). Data acquired with ZEISS Sigma FE-SEM.

3D Renderings of Drosophila Tactile Bristles

After acquisition of the 2D images and segmentation of the cell types, Dr. Mangione generated 3D rendering of the sensory organ at different timepoints during differentiation to track the nuances of the development of this tiny structure.

The 3D renderings unveiled remarkable changes in the morphology of the tactile bristle throughout development, particularly of the F-Cell. As differentiation progresses, the F-Cell extended its contact with the socket cell, to finally ensheath most of the tactile bristle by the end of differentiation.

3D peeling animation of the cellular assembly of the differentiating tactile organs. F-Cell (magenta), socket cell (green), shaft cell (light blue), sheath cell (orange), and neuron (yellow). Data acquired with ZEISS Sigma FE-SEM.

3D Peeling Animation Illustrates the Cellular Organization of the Tactile Bristle

As shown in this 3D peeling animation, the cells of the differentiating tactile bristle are arranged in a highly organized manner. The neuron (yellow) is progressively surrounded by the diverse cells making up the tactile organ, specifically by the sheath cell, the shaft cell, the socket cell, and the F-Cell. This organization is likely essential for touch sensation and neuronal function.

Dr. Mangione went on to perform electrophysiology studies to show that F-Cells are required for touch sensing.

Our efforts unambiguously showed the connection between the F-Cell and the bristle, and also illuminated the cellular assembly of the bristle itself. With SBF-SEM, we have gained essential insights into the 3D structure of the tactile bristle and the F-Cell for the first time.

Dr. Federica Mangione
Senior Postdoctoral Fellow, Apoptosis and Proliferation Control Laboratory, Francis Crick Institute, United Kingdom

Research team with pages from their publication in eLIFE — Pages from Dr. Mangione's article in *Nature Cell Biology*

Discovery of a New Cell Critical for Touch Sensing

By combining different microscopy technologies, Dr. Mangione was able to visualize the development of the Drosophila tactile bristle sensory organs within the epidermis.

Read her full article to see how she used live imaging and genetic labelling to track the differentiation of the sensory organs in vivo and shed light on its cellular organization, leading to her discovery of an additional cell type, the F-Cell.

Volume electron microscopy using SBF-SEM was used for morphology studies of the sensory organs during their development, and she was able to show that the F-Cell is co-opted into the tactile bristles and influence touch sensitivity in the adult fly.

Her findings show the importance of the F-Cells that she discovered in the assembly of functional touch-sensitive organs.