Zebrafish cornea formation and homeostasis reveal a slow maturation process, similarly to terrestrial vertebrates' corneas

Corneal blindness is the fourth leading cause of blindness worldwide. The superficial position of cornea on the eye makes this tissue prone to environmental aggressions, which can have a strong impact on sight. While most corneal pathology studies utilize terrestrial models, the knowledge on zebrafish cornea is too scarce to comprehend its strategy for the maintenance of a clear sight in aquatic environment. In this study, we deciphered the cellular and molecular events during corneal formation and maturation in zebrafish. After describing the morphological changes taking place from 3 days post fertilization (dpf) to adulthood, we analyzed cell proliferation. We showed that label retaining cells appear around 14 to 21dpf. Our cell proliferation study, combined to the study of Pax6a and krtt1c19e expression, demonstrate a long maturation process, ending after 45dpf. This maturation ends with a solid patterning of corneal innervation. Finally, we demonstrated that corneal wounding leads to an intense dedifferentiation, leading to the recapitulation of corneal formation and maturation, via a plasticity period. Altogether, our study deciphers the maturation steps of an aquatic cornea. These findings demonstrate the conservation of corneal formation, maturation and wound healing process in aquatic and terrestrial organisms, and they will enhance the use of zebrafish as model for corneal physiology studies.Peer reviewe

Zebrafish Corneal Wound Healing : From Abrasion to Wound Closure Imaging Analysis

As the transparent surface of the eye, the cornea is instrumental for clear sight. Due to its location, this tissue is prone to environmental insults. Indeed, the eye injuries most frequently encountered clinically are those to the cornea. While corneal wound healing has been extensively studied in small mammals (i.e., mice, rats, and rabbits), corneal physiology studies have neglected other species, including zebrafish, despite zebrafish being a classic research model. This report describes a method of performing a corneal abrasion on zebrafish. The wound is performed in vivo on anesthetized fish using an ocular burr. This method allows for a reproducible epithelial wound, leaving the rest of the eye intact. After abrasion, wound closure is monitored over the course of 3 h, after which the wound is reepithelialized. By using scanning electron microscopy, followed by image processing, the epithelial cell shape, and apical protrusions can be investigated to study the various steps during corneal epithelial wound closure. The characteristics of the zebrafish model permit study of the epithelial tissue physiology and the collective behavior of the epithelial cells when the tissue is challenged. Furthermore, the use of a model deprived of the influence of the tear film can produce new answers regarding corneal response to stress. Finally, this model also allows the delineation of the cellular and molecular events involved in any epithelial tissue subjected to a physical wound. This method can be applied to the evaluation of drug effectiveness in preclinical testing.Peer reviewe

Searching for optimal wintering conditions for young Finnraccoon females

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Resting preferences and welfare of Finnraccoon (Nyctereutes procyonoides ussuriensis) females housed in various housing conditions in winter

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Behaviour of the Finnraccoon females during winter

The aim of the study is to document the wintering behaviour in Finnraccoons (Nyctereutes procyonoides). A total of 40 juvenile Finnraccoon females were divided into four housing groups in mid-December: singly housing in a small cage (SC), singly housing in large cage (LC), singly housing in the large cage with access to a winter nest (WN) and social (pair) housing in the large cage (SH). All cages were furnished with an activity object, straw and platform. The behaviour of Finnraccoons was analysed for 24 hours in January and February by using instantaneous sampling. Linear mixed model was used for statistical analysis. Finnraccoons rested 69-75% of their time, without difference between groups (F3,36=0.33, P=0.806) or recordings (F1,36=2.15, P=0.151). The Finnraccoons in the SC and LC groups rested mainly on the cage floor (74-85% of the resting observations), WN group rested in the winter nest (95-98%) and SH group allohuddled (91-95%). More activity was observed in the SC and LC groups (11-12% of time) than in the WN group (9% of time), the SH group being in between (F3,36=3.90, P=0.016); but no difference between recordings (F1,36=2.66, P=0.112) was found. No difference between groups (F3,36=0.63, P=0.602; F3,36=0.64, P=0.595; F3,36=0.53, P=0.662), or recordings (F1,36=1.84, P=0.183, F1,36=0.13, P=0.724; F1,36=0.24, P=0.625) were found in sitting (9-15% of time), standing (5-7%) or stereotypic behaviour (<1-2%), respectively. The results show that Finnraccoon females prefer resting in the nest and allohuddling in winter. They are more active without these preferred resting options, but do not show more stereotypic behaviour.201