Cranial Nerve Development

Many genetic disorders are thought to disrupt behavior by compromising early steps in neural circuit development [1]. Resolving such cellular changes in early neural development has proven challenging with model organisms. Defining behaviors, circuits, and underlying developmental mechanisms in mutant mouse models that meaningfully parallel clinically significant deficits in human genetic disorders is difficult [1]. Detecting changes in initial differentiation of individual neurons remain elusive. These challenges are addressed by identifying early divergence of axon growth in a key component: the trigeminal nerve of the developing neural circuit [1]. By focusing on the trigeminal nerve (cranial nerve V), which is responsible for sensation of the face and motor functions, such as suckling, feeding, biting, chewing, and swallowing, axonal growth and pathfinding in the native, 3D environment that might otherwise be missed using histological processing, can be can investigated [1]. How rapid, high-contrast imaging of mouse embryos with a THUNDER Imager 3D Cell Culture and Large Volume Computational Clearing (LVCC) [2,3] can help the study of cranial nerve development is shown this article.

To image entire mouse embryos in a practical way, it is helpful to have a solution that can quickly achieve sharp, high-contrast 3D images where important details are clearly resolved. This way, the embryo can be captured in a single session and in a fraction of the time when compared to confocal imaging. Conventional widefield microscopy is fast and offers detection sensitivity, but images of thick specimens, like mouse embryos, often have an out-of-focus blur or haze which reduces the contrast [2,3].

Mouse embryos were imaged with a THUNDER Imager 3D Cell Culture. The embryos were stained with anti-βIII tubulin (Tuj1) antibody for mapping the nervous system and cranial nerves. Coupled with BABB clearing, the 3-dimensional structure of the nervous system in the entire embryo can be imaged. The images in figure 1 were collected with a 20x, multi-immersion media objective with a numerical aperture (NA) of 0.75 and a working distance close to 700 μm. The image consists of 32 stitched tiles with an imaging depth of 672 μm (337 steps), capturing the full extent of the embryo’s structure. All data was collected in a total time of 18 minutes.

The haze inherent to widefield imaging is extracted from the image via LVCC and Instant Computational Clearing (ICC) [2,3]. After clearing, the Leica adaptive deconvolution technology is used to enhance the resolution of the 3-dimenional features [4]. This processing allows for easy viewing of the neural structure of the embryo as well as more precious placement of the neurons within the embryo’s overall layout.

The THUNDER technology Large Volume Computational Clearing (LVCC) [2,3] significantly enhances the contrast when imaging cranial nerve development in mouse embryos allowing fine details to be resolved unlike conventional widefield imaging.

1. Z. Motahari, T.M. Maynard, A. Popratiloff, S.A. Moody, A.-S. LaMantia, Aberrant early growth of individual trigeminal sensory and motor axons in a series of mouse genetic models of 22q11.2 deletion syndrome, Human Molecular Genetics (2020) vol. 29, iss. 18, pp. 3081-3093, DOI: 10.1093/hmg/ddaa199.
2. J. Schumacher, L. Bertrand, THUNDER Technology Note: THUNDER Imagers: How Do They Really Work? Science Lab (2019) Leica Microsystems.
3. L. Felts, V. Kohli, J.M. Marr, J. Schumacher, O. Schlicker, An Introduction to Computational Clearing: A New Method to Remove Out-of-Focus Blur, Science Lab (2020) Leica Microsystems.
4. V. Kohli, J.M. Marr, O. Schlicker, L. Felts, The Power of Pairing Adaptive Deconvolution with Computational Clearing: Technical Brief, Science Lab (2021) Leica Microsystems.