Crosshair, semi-automated targeting for electron microscopy with a motorised ultramicrotome

Curation statements for this article:
  • Curated by eLife

    eLife logo

    Evaluation Summary:

    Meechan et al. present a systematic approach to semi-automate an ultramicrotome operation for targeting a specific plane aided by x-ray tomography measurements. It is a fundamental work of great interest to any users of using electron microscopy (EM), particularly when targeting the imaging of thin sections in a select region of interest by ultramicrotomy, or when targeting volume EM of select sample regions. The manuscript documents with exceptional detail a workflow including both microtome modifications and software adaptations for semi-automated targeting of structures with micrometer precision, resulting in a faster and more accurate orientation of the image acquisition planes for volume electron microscopy, a task that has traditionally been difficult and time-consuming. Therefore, this work will reduce sample preparation labor and, critically, facilitate the comparison of the ultrastructure of multiple samples. The method is based on X-ray imaging acquisition prior to any sectioning and proposes a solution for the two instruments commercially available in the field, and by transparently sharing all the data, hardware, and software, and by describing every detail of the workflow, this fundamental method can be readily adopted by any practitioner, enabling its wide application - it is a key step in the field regarding speed-up, accuracy, and reproducibility in electron microscopy.

    (This preprint has been reviewed by eLife. We include the public reviews from the reviewers here; the authors also receive private feedback with suggested changes to the manuscript. Reviewer #1, Reviewer #2 and Reviewer #3 agreed to share their names with the authors.)

This article has been Reviewed by the following groups

Read the full article See related articles

Abstract

Volume electron microscopy (EM) is a time-consuming process – often requiring weeks or months of continuous acquisition for large samples. In order to compare the ultrastructure of a number of individuals or conditions, acquisition times must therefore be reduced. For resin-embedded samples, one solution is to selectively target smaller regions of interest by trimming with an ultramicrotome. This is a difficult and labour-intensive process, requiring manual positioning of the diamond knife and sample, and much time and training to master. Here, we have developed a semi-automated workflow for targeting with a modified ultramicrotome. We adapted two recent commercial systems to add motors for each rotational axis (and also each translational axis for one system), allowing precise and automated movement. We also developed a user-friendly software to convert X-ray images of resin-embedded samples into angles and cutting depths for the ultramicrotome. This is provided as an open-source Fiji plugin called Crosshair. This workflow is demonstrated by targeting regions of interest in a series of Platynereis dumerilii samples.

Article activity feed

  1. Evaluation Summary:

    Meechan et al. present a systematic approach to semi-automate an ultramicrotome operation for targeting a specific plane aided by x-ray tomography measurements. It is a fundamental work of great interest to any users of using electron microscopy (EM), particularly when targeting the imaging of thin sections in a select region of interest by ultramicrotomy, or when targeting volume EM of select sample regions. The manuscript documents with exceptional detail a workflow including both microtome modifications and software adaptations for semi-automated targeting of structures with micrometer precision, resulting in a faster and more accurate orientation of the image acquisition planes for volume electron microscopy, a task that has traditionally been difficult and time-consuming. Therefore, this work will reduce sample …

  2. Reviewer #1 (Public Review):

    The authors of this paper are offering the electron microscopy community an affordable tool to semi-automatize some of the most challenging and time-consuming steps to target a region of interest in a sample prepared for electron microscopy. This article is sharing in total transparency all their work and the immense development efforts put in by the authors in terms of finance, manpower, software, and hardware development. A huge effort has been done to make all the parts of the workflow accessible. The way to add the hardware to the existing ultramicrotomes is clearly explained and documented. The hardware to be purchased and adapted is also clearly documented. All the software needed is open-source, the code fully documented and the implementation documented. A critical assessment of the performances is …

  3. Reviewer #2 (Public Review):

    For volume Electron Microscopy pipelines, an essential step is to target a specific plane within a resin specimen using an ultramicrotome. Up till now, this can only be done manually. Such a skill set requires months if not years of training and practice to master. This method paper is a pioneer work that offers a first step towards fully automated targeting of structures within resin blocks. It is well structured to document the targeting workflow in EM sample preparation, especially the video tutorial for the UC7 pipeline is professionally produced.

    Meechan et al. first described the workflow and techniques used to automate two models of ultramicrotomes (Leica EM UC7 and RMC PowerTome PC), which involve control of the rotations in three orthogonal axes via individual motors. They then integrated Crosshair, …

  4. Reviewer #3 (Public Review):

    Meechan et al. describe a technical modification of a standard ultramicrotome that allows, in combination with software solutions provided, both, the precise orientation and the depth of the cutting plane according to sample features pre-defined by X-ray imaging. Accurate targeting of specific structures in heavy-metal¬-impregnated volume EM samples is challenging and time-consuming and good reproducibility across samples is difficult. Since the applications for volume EM are rapidly increasing during the last years, improved workflows can have an important impact in the field.

    A great strength of the workflow described here is the easy access to the required components. Once X-ray data acquisition at a micron-resolution has been achieved, no further expensive, sophisticated equipment is required for its …