Morphological differences between the trabecular meshworks of zebrafish and mammals.
OBJECTIVE
The zebrafish has been used as an animal model to study ocular development and diseases, including glaucoma. However, there are still many concerns about the morphological differences between zebrafish and mammals. Before using the zebrafish for glaucoma studies, we should understand the morphological differences in the trabecular meshworks (TMs) of zebrafish and other animal models. This study investigated and compared the histological morphologies and compositions of the extracellular matrices of the TMs of the zebrafish and some commonly used animal models, including the mouse, rat, rabbit, and cow.


METHODS
Sections of the angular portions from the studied species (mouse, rat, rabbit, cow, zebrafish, and human) were prepared for immunohistochemical and electron microscopic analyses. Antibodies directed against cytoskeletal and extracellular matrix components (AE1/AE3, vimentin, alpha-smooth muscle actin, keratocan, and lumican) were used for immunolocalization. Reverse transcription polymerase chain reaction (RT-PCR) for keratocan and lumican was also performed.


RESULTS
The TMs of the mouse, rat, and human consist of extracellular matrix organized into a network of beams covered in trabecular endothelial cells. However, no lamellate meshwork exists in the TMs of the rabbit, cow, or zebrafish. Instead, a reticular meshwork (rabbit and cow) and an annular ligament (zebrafish) develop. Immunohistological analysis revealed that vimentin is expressed in the TMs of the rat, rabbit, and human, and alpha-smooth muscle actin is expressed in the TMs of the mouse, rat, rabbit, and human. Only the annular ligament of the zebrafish stained positively with anti-AE1/AE3 antibody. The annular ligament of the zebrafish also expresses keratocan and lumican. The human TM showed weakly positive staining of lumican. A prominent distribution of mitochondria and intracellular vacuoles is observed in the trabecular cells of the mouse, rat, rabbit, and cow, but not the zebrafish. The analysis of RT-PCR shows the keratocan and lumican mRNAs are expressed in the annular ligament of zebrafish, but not in mouse, rat, rabbit, and cow.


CONCLUSIONS
We conclude that the zebrafish expresses different extracellular matrix proteins and has a distinctive ultrastructure in the TM. Therefore, zebrafish should be used with caution for glaucoma studies.
Chen
Chun-Chen
CC
Department of Ophthalmology, Taipei City Hospital, Ren-Ai Branch, Taipei, Taiwan.
Yeh
Lung-Kun
LK
Liu
Chia-Yang
CY
Kao
Winston W-Y
WW
Samples
John R
JR
Lin
Shing-Jong
SJ
Hu
Fung-Rong
FR
Wang
I-Jong
IJ
D000818:Animals; D002417:Cattle; D005109:Extracellular Matrix / Q000378:metabolism / Q000648:ultrastructure*; D016326:Extracellular Matrix Proteins / Q000378:metabolism; D006801:Humans; D007124:Immunoenzyme Techniques; D051379:Mice; D008810:Mice, Inbred C57BL; D046529:Microscopy, Electron, Transmission; D011509:Proteoglycans / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D011817:Rabbits; D051381:Rats; D011922:Rats, Mutant Strains; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014129:Trabecular Meshwork / Q000166:cytology* / Q000378:metabolism; D015027:Zebrafish
D016326:Extracellular Matrix Proteins; D011509:Proteoglycans; D012333:RNA, Messenger