IFT46 plays an essential role in cilia development

Abstract

Cilia are microtubule-based structures that project into the extracellular space. Ciliary defects are associated with several human diseases, including polycystic kidney disease, primary ciliary dyskinesia, left-right axis patterning, hydrocephalus and retinal degeneration. However, the genetic and cellular biological control of ciliogenesis remains poorly understood. The IFT46 is one of the highly conserved intraflagellar transport complex B proteins. In zebrafish, ift46 is expressed in various ciliated tissues such as Kupffer’s vesicle, pronephric ducts, ears and spinal cord. We show that ift46 is localized to the basal body. Knockdown of ift46 gene results in multiple phenotypes associated with various ciliopathies including kidney cysts, pericardial edema and ventral axis curvature. In ift46 morphants, cilia in kidney and spinal canal are shortened and abnormal. Similar ciliary defects are observed in otic vesicles, lateral line hair cells, olfactory pits, but not in Kupffer’s vesicle. To explore the functions of Ift46 during mouse development, we have generated Ift46 knock-out mice. The Ift46 mutants have developmental defects in brain, neural tube and heart. In particular Ift46(−/−) homozygotes displays randomization of the embryo heart looping, which is a hallmark of defective left-right (L/R) axis patterning. Taken together, our results demonstrated that IFT46 has an essential role in vertebrate ciliary development.

The Intraflagellar Transport Machinery

“…In agreement with this notion, a direct interaction between IFT46 and the ODA assembly factor ODA16 was detected both by yeast-two-hybrid analysis as well as by pulldowns using recombinantly expressed proteins (Ahmed et al 2008), but further examination of amino-terminal and carboxy-terminal IFT46 domains was not published. IFT46 knockdown in zebrafish was recently shown to lead to a similar shortening of cilia in various organs and to several phenotypes indicative of motility defects (e.g., left -right asymmetry defects), but analysis of the axonemal ultrastructure did not show an obvious ODA assembly defect (Lee et al 2015).…”

IFT56 regulates vertebrate developmental patterning by maintaining IFTB complex integrity and ciliary microtubule architecture

“…This is unexpected, as IFTA proteins have long been thought to enter cilia together with IFTB proteins through the function of kinesin 2 (Blacque et al, 2008;Hsiao et al, 2012). In mice, most IFTB and kinesin 2 mutants lose cilia (Berbari et al, 2011;Botilde et al, 2013;Houde et al, 2006;Huangfu et al, 2003;Lee et al, 2015;Marszalek et al, 1999), suggesting that IFTB and kinesin 2 are crucial for the anterograde transport of cilia proteins and ciliogenesis. IFTA and dynein mouse mutants have short, bulbous cilia that accumulate IFT proteins (Cortellino et al, 2009;May et al, 2005;Mill et al, 2011;Qin et al, 2011;Tran et al, 2008), implicating a role in retrograde transport and the recycling of ciliary proteins.…”

IFT46 plays crucial roles in craniofacial and cilia development

“…Knockdown of IFT46 causes unstable complex B structure, loss of the outer dynein arm in the cilia [26], and shortened cilia in numerous ciliated tissues including Kupffer's vesicle, pronephric ducts, ears, and spinal cord [22]; however, effects of IFT46 on embryogenesis need further investigation.…”

“…Cterminus deletion construct of IFT46 showed unstable complex B structure, whereas N-terminus deletion construct showed a loss of the outer dynein arms in the cilium of C. reinhardtii [21]. Recent reports suggest that IFT46 knockdown induces the shortening of cilia in various ciliated tissues such as Kupffer's vesicle, pronephric ducts, ears, and spinal cord of zebrafish [22].…”