Nanoscale imaging of all anatomical structures over whole vertebrates is needed for a systematic understanding of human diseases, but this has not yet been achieved. Here, we demonstrate whole-ExM, which enables nanoscale imaging of all anatomical structures of whole zebrafish larvae by labeling the proteins of the larvae with fluorophores and expanding them four-fold. We first optimize the fluorophore selection and labeling procedure to visualize a broader range of anatomical structures. We then develop an expansion protocol for zebrafish larvae having calcified body parts. Through this process, we visualize the nanoscale details of diverse larvae organs, which have corresponding organ counterparts in humans, over the intact larvae. We show that whole-ExM retains the fluorescence signals of fluorescent proteins, and its resolution is high enough to visualize various structures that can be imaged only with electron microscopy. Whole-ExM would enable the nanoscale study of the molecular mechanisms of human diseases.
Glaucoma surgeries, such as trabeculectomy, are performed to lower the intraocular pressure to reduce the risk of vision loss. The surgeries create a new passage in the eye that reroutes the aqueous humor outflow to the subconjunctival space, where the fluid is presumably absorbed by the conjunctival lymphatics. However, the current knowledge of these ocular surface lymphatics remains limited. Here, we characterized the biology and function of the ocular lymphatics using transgenic lymphatic reporter mice and rats. We found that the limbal and conjunctival lymphatic networks are progressively formed by a primary lymphatic vessel that grows out from the nasal-side medial canthus region at the time of birth. This primary lymphatic vessel immediately branches out and invades the limbus and conjunctiva, and then simultaneously encircles the cornea in a bidirectional manner. As a result, the distribution of the ocular lymphatic is significantly polarized toward the nasal side, and the limbal lymphatics are directly connected to the conjunctival lymphatics. New lymphatic spouts are mainly produced from the nasal-side limbal lymphatics, posing the nasal side of the eye more responsive to fluid drainage and inflammatory stimuli. Consistently, when a fluorescent tracer was injected, fluid clearance was much more efficient in the nasal side than the temporal side of the eyes. In comparison, blood vessels are evenly distributed on the front surface of the eyes. We found that these distinct vascular distribution patterns were also conserved in human eyes. Together, our study demonstrated that the ocular surface lymphatics are more densely present in the nasal side and uncovered the potential clinical benefits in selecting the nasal side as a surgical site for glaucoma surgeries to improve the fluid drainage.
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