Loss of Ift74 Leads to Slow Photoreceptor Degeneration and Ciliogenesis Defects in Zebrafish

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.

Male germ cell-associated kinase (MAK) is required for axoneme formation during ciliogenesis in zebrafish photoreceptors

“…However, there are a few exceptions. In zebrafish mutants of an IFT-B component, IFT88 (also named oval), Traf3ip1 (also named elipsa), and a Kinesin II family protein Kif3a, the axoneme and the OS are totally absent in photoreceptors (Krock and Perkins, 2008;Omori et al, 2008;Sukumaran and Perkins, 2009;Zhu et al, 2021).…”

“…However, there are a few exceptions. In zebrafish mutants of an IFT-B component, IFT88 (also named oval ), Traf3ip1 (also named elipsa ), and a Kinesin II family protein Kif3a, the axoneme and the OS are totally absent in photoreceptors (Krock and Perkins, 2008; Omori et al, 2008; Sukumaran and Perkins, 2009; Zhu et al, 2021). Interestingly, in IFT88 ( oval ) and Traf3ip1 ( elipsa ) mutants, a single spot-like γ-tubulin or centrin signal is detected in the apical region of photoreceptors, similar to zebrafish mak mutants, suggesting that basal bodies are formed in both mutants (Omori et al, 2008; Sukumaran and Perkins, 2009; Tsujikawa and Malicki, 2004).…”

“…Because cilia work as “rail tracks” in IFT-mediated trafficking, disruption of cilia affects IFT and further causes photoreceptor degeneration, suggesting that the structural and functional integrity of the connecting cilium is indispensable for photoreceptor functions and maintenance. Although many other factors reportedly regulate photoreceptor cilia integrity (Cideciyan et al, 2007; den Hollander et al, 2006; Gao J., 2002; Gorden et al, 2008; Kakakhel et al, 2020; Rao et al, 2015; Zhu et al, 2021), the underlying mechanisms are not fully understood.…”

Ependymal polarity defects coupled with disorganized ciliary beating drive abnormal cerebrospinal fluid flow and spine curvature in zebrafish

“…Zebrafish mutants were generated using CRISPR/Cas9 method with the following target sequences: ccdc57: 5 0 -GGGAAGAGGTCAGTGAGCTT -3 0 , ofd1: 5 0 -TATCAGACCTTCAAGAGCCG-3 0 , tmem67:5 0 -GGCAAGTGTCAGTGTCCTGA-3 0 . Cilia mutants (MZkif3a, ift74, ift88, and uts2r3) and Tg (urp1: GAL4; UAS: Kaede) transgenic lines were the same as previously reported [8,9,[55][56][57].…”

The role of cilia during organogenesis in zebrafish

“…Further studies have revealed that ift57 mutants form short outer segments but fail to maintain them, leading to rapid photoreceptor degeneration [ 110 , 111 ]. Both ift74 morphants and ift74 mutants exhibit outer segment degeneration [ 112 , 113 ]. Ift80 morphants fail to form outer segments, ultimately resulting in the apoptosis of photoreceptors [ 114 ].…”