Abstract
Cilia are microtubule-based structures projecting from the cell surface that perform diverse biological functions. Ciliary defects can cause a wide range of genetic disorders known collectively as ciliopathies. Intraflagellar transport (IFT) proteins are essential for the assembly and maintenance of cilia by transporting proteins along the axoneme. Here, we report a lack of Ift74, a core IFT-B protein, leading to ciliogenesis defects in multiple organs during early zebrafish development. Unlike rapid photoreceptor cell death in other ift-b mutants, the photoreceptors of ift74 mutants exhibited a slow degeneration process. Further experiments demonstrated that the connecting cilia of ift74 mutants were initially formed but failed to maintain, which resulted in slow opsin transport efficiency and eventually led to photoreceptor cell death. We also showed that the large amount of maternal ift74 transcripts deposited in zebrafish eggs account for the main reason of slow photoreceptor degeneration in the mutants. Together, our data suggested Ift74 is critical for ciliogenesis and that Ift proteins play variable roles in different types of cilia during early zebrafish development. To our knowledge, this is the first study to show ift-b mutant that displays slow photoreceptor degeneration in zebrafish.
Highlights
Accepted: 23 August 2021Retinal degeneration is one of the major causes of human blindness due to progressive death and dysfunction of photoreceptors
We found that ift74, encoding a component of the Intraflagellar transport (IFT)-B core complex, is located in this region
Being a key member of the core IFT‐B complex, the role of Ift74 during intraflagellar transport has been extensively investigated, while less is known about its roles during early embryonic development
Summary
Retinal degeneration is one of the major causes of human blindness due to progressive death and dysfunction of photoreceptors. The vertebrate photoreceptor cell is a specialized type of neuroepithelial cell with a distinctive morphology, consisting of an outer segment (OS), inner segment (IS), the nuclear region, and synapse. OS can be recognized as a highly modified sensory cilium that is rich in the photosensitive G protein-coupled receptors (GPCRs), opsins. The OS and IS are connected through a narrow structure called the connecting cilium, through which opsin and other OS protein components synthesized in the IS can be transported into the OS [1,2]. Cilia are highly conserved organelles extending from the surface of almost all vertebrate cells. Cilia are often classified as either motile or primary (sensory) cilia
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