Purpose
To establish optical coherence tomography (OCT) as an
in vivo
imaging modality for investigating the process of newt lens regeneration.
Methods
Spectral-domain OCT was employed for
in vivo
imaging of the newt lens regeneration process. A total of 37 newts were lentectomized and followed by OCT imaging over the course of 60 to 80 days. Histological images were obtained at several time points to compare with the corresponding OCT images. Volume measurements were also acquired.
Results
OCT can identify the key features observed in corresponding histological images based on the scattering differences from various eye tissues, such as the cornea, intact and regenerated lens, and the iris. Lens volume measurements from three-dimensional OCT images showed that the regenerating lens size increased linearly until 60 days post-lentectomy.
Conclusions
Using OCT imaging, we were able to track the entire process of newt lens regeneration
in vivo
for the first time. Three-dimensional OCT images allowed us to volumetrically quantify and visualize the dynamic spatial relationships between tissues during the regeneration process. Our results establish OCT as
an
in vivo
imaging modality to track/analyze the entire lens regeneration process from the same animal.
Translational Relevance
Lens regeneration in newts represents a unique example of vertebrate tissue plasticity. Investigating the cellular and morphological events that govern this extraordinary process
in vivo
will advance our understanding and shed light on developing new therapies to treat blinding disorders in higher vertebrates.
Humans and other tetrapods are considered to require apical-ectodermal-ridge, AER, cells for limb development, and AER-like cells are suggested to be re-formed to initiate limb regeneration. Paradoxically, the presence of AER in the axolotl, the primary regeneration model organism, remains controversial. Here, by leveraging a single-cell transcriptomics-based multi-species atlas, composed of axolotl, human, mouse, chicken, and frog cells, we first established that axolotls contain cells with AER characteristics. Surprisingly, further analyses and spatial transcriptomics revealed that axolotl limbs do not fully re-form AER cells during regeneration. Moreover, the axolotl mesoderm displays part of the AER machinery, revealing a novel program for limb (re)growth. These results clarify the debate about the axolotl AER and the extent to which the limb developmental program is recapitulated during regeneration.
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