Abstract
Simple SummaryMyocilin is a protein with an incompletely understood function, mainly known because of its role in glaucoma. In this study we have analysed the normal role of this protein in vivo. To that end, we generated the first myocilin knockout zebrafish line reported to date. This zebrafish line did not show any apparent gross morphological anomaly, but unexpectedly, we observed that all knockout animals were males. Detailed analyses revealed the existence of apoptosis in the immature juvenile gonad, which is associated with male differentiation. Moreover, we demonstrate that adult knockout differentially expressed key genes involved both in male sex determination and the Wnt signalling pathway, which also plays a role in zebrafish gonad differentiation. Altogether, these results indicate that myocilin is a novel key protein involved in sex determination in zebrafish. Myocilin is a secreted glycoprotein with a poorly understood biological function and it is mainly known as the first glaucoma gene. To explore the normal role of this protein in vivo we developed a myoc knockout (KO) zebrafish line using CRISPR/Cas9 genome editing. This line carries a homozygous variant (c.236_239delinsAAAGGGGAAGGGGA) that is predicted to result in a loss-of-function of the protein because of a premature termination codon p.(V75EfsX60) that resulted in a significant reduction of myoc mRNA levels. Immunohistochemistry showed the presence of myocilin in wild-type embryonic (96 h post-fertilization) anterior segment eye structures and caudal muscles. The protein was also detected in different adult ocular and non-ocular tissues. No gross macroscopic or microscopic alterations were identified in the KO zebrafish, but, remarkably, we observed absence of females among the adult KO animals and apoptosis in the immature juvenile gonad (28 dpf) of these animals, which is characteristic of male development. Transcriptomic analysis showed that adult KO males overexpressed key genes involved in male sex determination and presented differentially expressed Wnt signalling genes. These results show that myocilin is required for ovary differentiation in zebrafish and provides in vivo support for the role of myocilin as a Wnt signalling pathway modulator. In summary, this myoc KO zebrafish line can be useful to investigate the elusive function of this protein, and it provides evidence for the unexpected function of myocilin as a key factor in zebrafish sex determination.
Highlights
Myocilin is a 55–57 kDa extracellular glycoprotein with an enigmatic function and was identified in 1997 as the first glaucoma gene [1]
C-terminal myocilin fragments have been identified in different ocular tissues and biological fluids such as the ciliary body, aqueous humor (AH) [11] and trabecular meshwork [9], indicating that the proteolytic cleavage of this protein occurs in vivo and that it may be important in regulating its biological function
We found that while this line did not show apparent morphological anomalies, unexpectedly, all KO animals were males, indicating that myocilin is required for ovary differentiation, acting as a novel key protein involved in sex determination in domesticated zebrafish
Summary
Myocilin is a 55–57 kDa extracellular glycoprotein with an enigmatic function and was identified in 1997 as the first glaucoma gene [1]. Glaucoma is a progressive and irreversible optic neuropathy that is caused by apoptosis of retinal ganglion cells, and it is generally associated with elevated intraocular pressure [2] This protein was identified in human trabecular meshwork cell cultures that were treated with glucocorticoids, and it was initially called Trabecular Meshwork Inducible Glucocorticoid Response (TIGR) [3]. C-terminal myocilin fragments have been identified in different ocular tissues and biological fluids such as the ciliary body, aqueous humor (AH) [11] and trabecular meshwork [9], indicating that the proteolytic cleavage of this protein occurs in vivo and that it may be important in regulating its biological function. To the best of our knowledge, our results provide the first in vivo evidence of myocilin as a Wnt signalling pathway modulator
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
