Distinct functions for IFT140 and IFT20 in opsin transport

Crouse, Jacquelin A.; Lopes, Vanda S.; SanAgustin, Jovenal T.; Keady, Brian T.; Williams, David S.; Pazour, Gregory J.

doi:10.1002/cm.21173

Cited by 49 publications

(53 citation statements)

References 34 publications

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“…These data demonstrate that the IFT process is critical for proper photoreceptor function and explain the vulnerability of photoreceptor cells to disruption of ciliary genes. Consistent with this notion, in a recent study, acute deletion of ift140 in cone photoreceptors of adult mice causes abnormal accumulation of opsins in the nuclear layer and the IS (Crouse et al 2014), suggesting disrupted protein transport as a potential mechanism of retinal degeneration caused by IFT140 deficiency. In addition to its function in adult photoreceptor maintenance, IFT140 is also likely involved in early photoreceptor development based on its critical role during ciliogenesis (Miller et al 2013).…”

Section: Discussionmentioning

confidence: 54%

Mutations in human IFT140 cause non-syndromic retinal degeneration

Yang

Wang

et al. 2015

Hum Genet

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Leber congenital amaurosis (LCA) and retinitis pigmentosa (RP) are two genetically heterogeneous retinal degenerative disorders. Despite the identification of a number of genes involved in LCA and RP, the genetic etiology remains unknown in many patients. In this study, we aimed to identify novel disease-causing genes of LCA and RP. Retinal capture sequencing was initially performed to screen mutations in known disease-causing genes in different cohorts of LCA and RP patients. For patients with negative results, we performed whole exome sequencing and applied a series of variant filtering strategies. Sanger sequencing was done to validate candidate causative IFT140 variants. Exome sequencing data analysis led to the identification of IFT140 variants in multiple unrelated non-syndromic LCA and RP cases. All the variants are extremely rare and predicted to be damaging. All the variants passed Sanger validation and segregation tests provided that the family members’ DNA was available. The results expand the phenotype spectrum of IFT140 mutations to non-syndromic retinal degeneration, thus extending our understanding of intraflagellar transport and primary cilia biology in the retina. This work also improves the molecular diagnosis of retinal degenerative disease.

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Section: Discussionmentioning

confidence: 54%

Mutations in human IFT140 cause non-syndromic retinal degeneration

Yang

Wang

et al. 2015

Hum Genet

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“…Interestingly, only IFT20-GFP displayed ciliary transport properties that were not blocked by forced dimerization of NUP62-Fv (Figure 3E). IFT20 is thought to be a peripheral component of the IFT-B subcomplex [23] and has been proposed to play a role in sorting of ciliary proteins at the Golgi complex [25–29]. Thus, IFT20-GFP could gain access to the cilium via its interaction with membrane proteins rather than as a cytosolic IFT component.…”

Section: Resultsmentioning

confidence: 99%

An Assay for Clogging the Ciliary Pore Complex Distinguishes Mechanisms of Cytosolic and Membrane Protein Entry

et al. 2014

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Summary As a cellular organelle, the cilium contains a unique protein composition [1, 2]. Entry of both membrane [3–5] and cytosolic components [6–8] is tightly regulated by gating mechanisms at the cilium base, however, the mechanistic details of ciliary gating are largely unknown. We previously proposed that entry of cytosolic components is regulated by mechanisms similar to those of nuclear transport and is dependent on nucleoporins (NUPs) which comprise a ciliary pore complex (CPC) [6, 9]. To investigate ciliary gating mechanisms, we developed a system to clog the pore by inhibiting NUP function via forced dimerization. We targeted NUP62, a component of the central channel of the nuclear pore complex (NPC) [10], for forced dimerization by tagging it with the homodimerizing Fv domain. As proof of principle, we show that forced dimerization of NUP62-Fv attenuated active transport of bovine serum albumin into the nuclear compartment and of the kinesin-2 motor KIF17 into the ciliary compartment. Using the pore clogging technique, we find that forced dimerization of NUP62 attenuated the gated entry of cytosolic proteins but did not affect entry of membrane proteins or diffusional entry of small cytosolic proteins. We propose a model in which active transport of cytosolic proteins into both nuclear and ciliary compartments requires functional NUPs of the central pore whereas lateral entry of membrane proteins utilizes a different mechanism that is likely specific to each organelle’s limiting membrane.

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“…Both conditional knockout alleles used here have been used successfully in previous studies to address the role of mTORC1 and mTORC2 in various tissues (Bentzinger et al, 2008; Cybulski et al, 2009; Romanino et al, 2011; Thomanetz et al, 2013; Venkatesh et al, 2015). Similarly, the M-Cre + line has been used successfully to study the role of various genes in cones (Busskamp et al, 2014; Crouse et al, 2014; Ivanovic et al, 2011; Venkatesh et al, 2015). To verify that CRE recombinase is active in all cones across the retina we first crossed the M-Cre +/− line to the Ai9 Cre-reporter line (Madisen et al, 2010), which expresses tdTomato upon CRE recombinase expression.…”

Section: Resultsmentioning

confidence: 99%

Loss of mTOR signaling affects cone function, cone structure and expression of cone specific proteins without affecting cone survival

Venkatesh

Langellotto

et al. 2015

Experimental Eye Research

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Cones are the primary photoreceptor (PR) cells responsible for vision in humans. They are metabolically highly active requiring phosphoinositide 3-kinase (PI3K) activity for long-term survival. One of the downstream targets of PI3K is the kinase mammalian target of rapamycin (mTOR), which is a key regulator of cell metabolism and growth, integrating nutrient availability and growth factor signals. Both PI3K and mTOR are part of the insulin/mTOR signaling pathway, however if mTOR is required for long-term PR survival remains unknown. This is of particular interest since deregulation of this pathway in diabetes results in reduced PR function before the onset of any clinical signs of diabetic retinopathy. mTOR is found in two distinct complexes (mTORC1 & mTORC2) that are characterized by their unique accessory proteins RAPTOR and RICTOR respectively. mTORC1 regulates mainly cell metabolism in response to nutrient availability and growth factor signals, while mTORC2 regulates pro-survival mechanisms in response to growth factors. Here we analyze the effect on cones of loss of mTORC1, mTORC2 and simultaneous loss of mTORC1 & mTORC2. Interestingly, neither loss of mTORC1 nor mTORC2 affects cone function or survival at one year of age. However, outer and inner segment morphology is affected upon loss of either complex. In contrast, concurrent loss of mTORC1 and mTORC2 leads to a reduction in cone function without affecting cone viability. The data indicates that PI3K mediated pro-survival signals diverge upstream of both mTOR complexes in cones, suggesting that they are independent of mTOR activity. Furthermore, the data may help explain why PR function is reduced in diabetes, which can lead to deregulation of both mTOR complexes simultaneously. Finally, although mTOR is a key regulator of cell metabolism, and PRs are metabolically highly active, the data suggests that the role of mTOR in regulating the metabolic transcriptome in healthy cones is minimal.

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Distinct functions for IFT140 and IFT20 in opsin transport

Cited by 49 publications

References 34 publications

Mutations in human IFT140 cause non-syndromic retinal degeneration

Mutations in human IFT140 cause non-syndromic retinal degeneration

An Assay for Clogging the Ciliary Pore Complex Distinguishes Mechanisms of Cytosolic and Membrane Protein Entry

Loss of mTOR signaling affects cone function, cone structure and expression of cone specific proteins without affecting cone survival

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