Cellular activity of autophagy and multivesicular bodies in lens fiber cells during early lens development in rbm24a mutant of zebrafish: Ultrastructure analysis

Abstract

Use of zebrafish as animal model for various diseases during early developmental stages has been exponentially increased with the aim to achieve the best representative results in this transparent fish. Recent studies documented that Rbm24a mutant causes cataract formation and resulted in blindness using the zebrafish model. Therefore, correct interpretation of studies that aimed for molecular approaches, a description of comparative and in-depth analysis of development of lens in wildtype and mutant is crucial to obtain the correct conclusion. In this study, we use a gold standard method the Transmission Electron Microscopy (TEM) to analysis the lens development in rbm24a mutant zebrafish. Firstly, we compare the cellular structures at 16-20 h post fertilization (hpf), the lens placode in ectoderm indicated delay lens development in rbm24a mutant than wildtype (siblings) zebrafish. At 33 hpf, loosely appeared lens fiber cells showed heterogenous electron density with numbers of mitochondria in lens of rbm24a mutant, revealed the influence of gene mutation in lens development. A detail ultrastructure of lens of rbm24a mutant also presented at 33 hpf. Comparatively in wildtype (siblings) at 33 hpf, lens exhibited homogenous electron density in tightly packed lens fiber cells with few mitochondria. Furthermore, to characterize the lens in rbm24a mutant we obtained data of cellular structures on 25 hpf and 1.5 days' post fertilization (dpf). At 25 hpf in mutant zebrafish, the detached solid sphere lens mass from ectoderm showed karyorrhexis, mitophagy and vesicles (also multivesicular bodies), these cellular structures supposed to hamper the development of future fiber cells. Moreover, at 1.5 dpf in mutant, nuclear excisosome, multilamellar bodies and irregular shaped mitochondria in heterogenous electron dense cytoplasm of lens fiber cells, collectively shown affected lens transparency. In summary the ultrastructure results of lens of rbm24a mutant zebrafish expand our knowledge and give reflection of different cellular activities like autophagy, apoptosis, vesicles (multivesicular bodies) and nuclear excisosomes which play their role in transparency achievement.

Keywords: Apoptosis; Autophagy; Lens; Nuclear excisosomes; Zebrafish; rbm24a.