Generated using OpenAI Deep Research API
The INTU gene (also known as inturned, PDZD6, or CPLANE4) encodes a planar cell polarity effector protein crucial for ciliogenesis and embryonic development (reactome.org) (pmc.ncbi.nlm.nih.gov). INTU plays a key role in forming primary cilia by controlling the organization of the apical actin cytoskeleton and positioning basal bodies at the apical cell surface (reactome.org). This function is essential for the normal orientation and elongation of ciliary microtubules needed to transduce Hedgehog (Hh) signals (reactome.org) (pmc.ncbi.nlm.nih.gov). Indeed, loss of Intu causes almost complete absence of primary cilia and a corresponding suppression of Hh signaling in certain cells (pmc.ncbi.nlm.nih.gov), highlighting that Intu’s effect on Hh is indirect via its role in cilium assembly (corona-2.cansar.icr.ac.uk). Notably, INTU is a planar cell polarity (PCP) effector required for defining cell polarity through ciliogenesis, although it is apparently not involved in the convergent extension movements mediated by core PCP components (corona-2.cansar.icr.ac.uk). This suggests INTU influences polarized cell behaviors mainly by enabling cilia formation and orientation, rather than directly altering cell movements.
Molecularly, Intu is proposed to function as a core component of the CPLANE complex (“ciliogenesis and planar polarity effector” complex) that recruits intraflagellar transport (IFT) machinery to basal bodies (reactome.org). Intu physically interacts with fellow PCP effector proteins Fuz and WDPCP, forming the CPLANE complex scaffold at the ciliary base (corona-2.cansar.icr.ac.uk). Through this complex, Intu specifically helps recruit the IFT-A subunits (peripheral intraflagellar transport A proteins) to the mother centriole/basal body, a critical step for ciliogenesis (reactome.org). For example, affinity purification of Intu in ciliated cells pulls down all six IFT-A complex subunits (but not IFT-B), demonstrating Intu’s role in assembling the IFT machinery at the ciliary base (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). Additionally, Intu interacts with other ciliopathy proteins like JBTS17 (also called CPLANE1) and RSG1 in organizing the ciliary assembly hierarchy (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). Intu and its partner WDPCP are mutually required for each other’s localization to basal bodies, indicating a cooperative mechanism in anchoring the CPLANE complex (pmc.ncbi.nlm.nih.gov).
Beyond IFT recruitment, Intu serves as an adaptor linking the ciliary apparatus to the actin cytoskeleton. In multiciliated epithelial cells, Intu localizes near basal bodies and mediates a ternary complex between the ciliary base protein NPHP4 and the actin-nucleating factor DAAM1 (pmc.ncbi.nlm.nih.gov). This Intu–NPHP4–DAAM1 complex is crucial for rearranging the subapical actin network that supports basal body docking and coordinated ciliary beating (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). Intu appears to couple cilia-associated proteins to actin regulators, ensuring the apical actin web is properly organized for ciliogenesis and cilium positioning (pmc.ncbi.nlm.nih.gov). Consistently, Intu depletion leads to disorganized or thinned apical actin, defective basal body docking, and reduced ciliogenesis, phenocopying the effects of Nphp4 or Daam1 loss (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). Intu also recruits the small GTPase RhoA to the apical cortex during multiciliogenesis; without Intu, RhoA fails to localize apically, which impairs actin polymerization at the cell apex (pmc.ncbi.nlm.nih.gov). Through these mechanisms, Intu coordinates cytoskeletal dynamics with ciliary assembly, thereby influencing planar polarization of cilia across cell fields (pmc.ncbi.nlm.nih.gov).
In summary, INTU’s molecular function is as a scaffold protein in cilium formation and planar polarity pathways. It is predicted to bind phosphatidylinositol lipids (a possible membrane association function) (www.ncbi.nlm.nih.gov), and it facilitates multiple protein–protein interactions via its domains (see below). By integrating with other CPLANE components and cytoskeletal regulators, Intu ensures that cilia are built, positioned, and oriented correctly, which is vital for downstream signaling pathways and developmental patterning.
Intu protein is primarily localized at the base of cilia within cells. It concentrates around the mother centriole/basal body of both primary cilia and motile cilia (www.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). For example, in multiciliated epithelial cells, fluorescently tagged Intu was observed robustly around the basal bodies just below each ciliary axoneme (pmc.ncbi.nlm.nih.gov). Intu’s presence at basal bodies is interdependent with other CPLANE proteins (e.g., Wdpcp), as each is required for the other’s proper anchoring to the centriole area (pmc.ncbi.nlm.nih.gov). High-resolution imaging in Xenopus multiciliated cells showed Intu localized to a region just distal to the basal body, at the apical membrane where the cilium emerges (pmc.ncbi.nlm.nih.gov). This positioning allows Intu to interface with both the ciliary enterprising structures (transition zone/IFT machinery) and the subapical actin network.
In addition to basal body localization, a portion of Intu is found in the cytosol (www.ncbi.nlm.nih.gov). The cytosolic fraction likely represents Intu that is not yet assembled at cilia or is in transit as part of protein complexes. Intu may shuttle between the cytosol and the ciliary base as needed for ciliogenesis. Notably, Intu has been detected at motile cilia as well (www.ncbi.nlm.nih.gov), consistent with its role in cells bearing multiple motile cilia (such as airway epithelial cells or embryonic node cells). In these cells, Intu localizes to the apical cortex at each basal body, thereby participating in the polarized alignment of motile ciliary arrays (pmc.ncbi.nlm.nih.gov). There is no evidence that Intu localizes to the nucleus or other organelles; instead, it is concentrated at the cell’s apical domain where ciliary organelles and associated structures reside.
Overall, INTU is a cytoplasmic protein enriched at the ciliary base, specifically the basal body/centriolar complex of both primary and motile cilia. This subcellular localization underpins its role in assembling ciliary components and organizing the apical cell cortex. Its presence at the basal body–actin interface positions Intu perfectly to coordinate the structural elements required for cilium formation and orientation in polarized cells.
Intu is involved in several key biological processes, primarily related to cilium formation and developmental patterning. Foremost, INTU is required for ciliogenesis, the process of building a cilium. Genetic studies in mice have shown that Intu is essential for the biogenesis of primary cilia in many cell types (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). When Intu is absent, cells fail to form normal ciliary axonemes even though basal bodies may dock, leading to a loss of functional cilia (pmc.ncbi.nlm.nih.gov). Intu thereby participates in intraciliary transport and assembly: it helps recruit the IFT-A transport proteins necessary to extend the ciliary axoneme (pmc.ncbi.nlm.nih.gov). Intu’s role in ciliogenesis directly impacts the Hedgehog (Hh) signaling pathway, since primary cilia are required for Hh signal transduction. Intu-deficient mouse embryos exhibit severely impaired Hh signaling and downstream gene expression, due to the absence of cilia needed for pathway activation (pmc.ncbi.nlm.nih.gov). In specific contexts like skin, removal of Intu abolishes primary cilia on keratinocytes and suppresses Hh-dependent hair follicle differentiation, demonstrating a cilia-mediated effect on developmental signaling (pmc.ncbi.nlm.nih.gov).
As a PCP effector, INTU also contributes to establishing planar cell polarity in tissues. It is needed for the proper orientation of cilia and basal bodies across the epithelial plane. In multiciliated cells, Intu is required for the coordinated polarization of cilia, ensuring they beat in the same direction (pmc.ncbi.nlm.nih.gov). Loss of Intu in these cells leads to misaligned cilia and disrupted directional fluid flow, due to defects in actin-based basal body positioning (pmc.ncbi.nlm.nih.gov). Intu does not appear to regulate the convergent-extension movements of cells themselves (a separate aspect of PCP), but it defines cell polarity via its ciliogenic role (corona-2.cansar.icr.ac.uk). By organizing apical actin and recruiting RhoA, Intu influences how each cell’s cilium is positioned relative to the tissue axis, thus participating in planar polarity cues (pmc.ncbi.nlm.nih.gov).
INTU is crucial for several embryonic developmental processes that are known to depend on cilia and PCP signaling. It is involved in embryonic digit morphogenesis – Intu mutant mice display polydactyly (extra digits), reflecting disrupted patterning of the limb bud (pmc.ncbi.nlm.nih.gov) (www.ncbi.nlm.nih.gov). Similarly, Intu plays a role in craniofacial development: it is required for normal roof of mouth (palate) development and tongue morphogenesis during embryogenesis (www.ncbi.nlm.nih.gov). Humans or mice lacking Intu function can exhibit a high-arched or cleft palate and tongue malformations (e.g. lingual nodules), linking Intu to these developmental processes. Intu also contributes to skeletal development, particularly through the Indian hedgehog (Ihh) pathway in cartilage: Intu hypomorphic mutant mice show delayed endochondral ossification in long bones and ribs, correlating with reduced Ihh signaling in growth plates (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). Additionally, Intu function in the embryonic node (which contains motile cilia) suggests a role in left-right axis specification, since node cilia defects often lead to laterality issues. Indeed, Intu mutant embryos have shorter and fewer nodal cilia (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov), which could perturb left-right signaling, although this may be context-dependent.
In summary, INTU is involved in cilium assembly and function, planar cell polarity, and cilia-dependent developmental pathways. Key GO Biological Process terms associated with INTU include cilium organization, intraciliary (intraflagellar) transport, Hedgehog signaling pathway, embryonic limb morphogenesis, palate development, and tongue development, among others (www.ncbi.nlm.nih.gov). The diverse developmental phenotypes of Intu disruption (polydactyly, craniofacial anomalies, skeletal defects) all stem from its fundamental role in building cilia and thereby enabling the signaling and polarity processes that guide embryogenesis.
Given its critical role in cilia, INTU is linked to human ciliopathy syndromes. Biallelic pathogenic variants in INTU cause a rare recessive disorder classified as Oral-Facial-Digital syndrome type XVII (OFD XVII) (pubmed.ncbi.nlm.nih.gov). OFD XVII is characterized by malformations of the oral cavity, face, and digits, consistent with ciliary dysfunction. Patients with INTU mutations present with developmental delay, craniofacial dysmorphisms (e.g. hypertelorism), a high-arched palate, tongue nodules or hamartomas, and polydactyly (extra fingers/toes) (pubmed.ncbi.nlm.nih.gov). Other features can include brain malformations, congenital heart defects, and kidney anomalies (pubmed.ncbi.nlm.nih.gov). This phenotype overlaps considerably with other oral-facial-digital syndromes and ciliopathies, underlining that INTU loss disrupts multiple organ systems during development.
INTU has also been implicated in a skeletal ciliopathy: Short-Rib Thoracic Dysplasia 20 with polydactyly (SRTD20) (pubmed.ncbi.nlm.nih.gov). SRTD20, also known as a form of Jeune asphyxiating thoracic dystrophy, is a lethal dwarfism syndrome involving shortened ribs (leading to a small thoracic cage), limb shortness, and polydactyly. At least two patients with this severe ciliopathy were found to carry homozygous loss-of-function mutations in INTU (pubmed.ncbi.nlm.nih.gov). Consistent with Intu’s role in chondrogenesis, these individuals showed thoracic skeletal hypoplasia and limb patterning defects. An INTU mutant patient reported in a 2016 study had compound heterozygous mutations (one nonsense and one missense) and presented with multiple congenital anomalies, including a narrow ribcage, polydactyly in all limbs, craniofacial abnormalities (such as microphthalmia and open fontanel), and cardiac defects (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). This clinical presentation aligns with the short-rib polydactyly spectrum and underscores INTU’s importance in thoracic and limb development.
Renal disease is another association: a homozygous missense variant in INTU was identified in one case of juvenile nephronophthisis, a cystic kidney disease (pmc.ncbi.nlm.nih.gov). The affected child developed end-stage renal failure by age 10, suggesting that even hypomorphic INTU alleles can lead to renal ciliopathy manifestations (nephronophthisis is typically caused by cilia-related genes). However, this INTU change was at a not well-conserved residue and might represent a milder, partially functional allele (pmc.ncbi.nlm.nih.gov). It indicates that INTU is also needed for normal kidney function, likely through maintaining the primary cilia of renal tubular cells.
Overall, INTU-related diseases reflect the hallmarks of ciliopathies: orofacial abnormalities, polydactyly, skeletal dysplasia, and cystic organ defects. These disorders are inherited in an autosomal recessive manner and are very rare. The link between INTU and such syndromes was established only recently, with a handful of families reported (pubmed.ncbi.nlm.nih.gov). Importantly, INTU lies in the same functional network as other ciliopathy genes (e.g., OFD6/CPLANE1, JBTS17), and mutations in these interacting partners can cause overlapping syndromes (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). Recognition of INTU’s involvement in human disease has expanded the genetic landscape of ciliopathies, designating OFD type XVII (OMIM #617925) and SRTD type 20 (OMIM #617952) as INTU-associated conditions. Future identification of additional patients will likely refine the clinical spectrum attributable to INTU mutations.
The INTU protein consists of 942 amino acids (pmc.ncbi.nlm.nih.gov) and contains a notable PDZ domain in its sequence. A predicted PDZ domain is located approximately at residues 199–262 of human Intu (www.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). PDZ domains are protein-interaction modules often binding to specific motifs at the C-termini of target proteins or sometimes to internal peptide sequences or lipids (www.ncbi.nlm.nih.gov). The presence of a PDZ domain suggests that Intu functions as a scaffold, anchoring other proteins (possibly those with PDZ-binding motifs) at the ciliary base or apical membrane. Indeed, many interactions of Intu (with FUZ, WDPCP, NPHP4, etc.) are likely mediated through regions like this PDZ domain and adjacent sequences that facilitate complex formation.
Aside from the PDZ domain, the remainder of Intu is largely composed of unique or low-complexity regions without well-characterized globular domains. It has a long C-terminal region (downstream of the PDZ) which is required for Intu’s function; for example, a point mutation near the C-terminus (Ile813Asn in mice) disrupts Intu’s ability to fully rescue ciliogenesis (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). This indicates that the C-terminal portion, though not a defined domain, is functionally important—potentially mediating interactions with cytoskeletal elements or other ciliary proteins. Intu’s C-terminus is rich in conserved hydrophobic residues (like the Ile813) that are maintained across species (pmc.ncbi.nlm.nih.gov), hinting that this region has structural or regulatory significance.
Bioinformatic analyses predict that Intu may have phosphoinositide-binding capacity (www.ncbi.nlm.nih.gov). While Intu is not known to contain a classic PH domain, the prediction of phosphatidylinositol binding suggests it could associate with membrane lipids at the ciliary base. This could stabilize Intu’s localization to the ciliary membrane or basal body area by binding to phosphoinositide-rich domains of the plasma membrane or ciliary pocket. Experimentally, Intu has been shown to recruit membrane-associated proteins like small GTPases (e.g. RhoA) to the apical membrane (pmc.ncbi.nlm.nih.gov), supporting the idea that it might interact with membrane components.
In terms of protein structure, no high-resolution structure of Intu is currently available, likely because it is a large scaffold protein with flexible regions. However, Intu belongs to the inturned family of proteins, sharing sequence homology with Drosophila Inturned and with other species’ orthologs that all contain PDZ domains. Intu lacks obvious enzymatic domains; its function comes from protein–protein interaction interfaces. The PDZ domain is a key interface, and additional stretches may form coiled-coils or bind specific partners (for instance, interaction with DAAM1 and NPHP4 involves the Intu C-terminus and perhaps adjacent motifs (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov)).
To summarize, INTU is structurally characterized by a central PDZ domain (a binding module) and extensive flanking regions that confer scaffolding ability. This architecture is well-suited for its role assembling multi-protein complexes at the ciliary base. The protein’s conserved length (~942 amino acids in human) and motifs emphasize functional regions that have been preserved evolutionarily for effective cilia formation and planar polarity signaling.
INTU is expressed broadly in human tissues, consistent with the widespread need for cilia in cell physiology. According to transcript profiling, INTU shows a ubiquitous expression pattern: it is detectable in many organs, with moderate levels in reproductive tissues (ovary, testis) and numerous others (www.ncbi.nlm.nih.gov). For instance, RNA-seq data indicate INTU mRNA is present in at least 26 different human tissues, albeit generally at modest levels (RPKM values in the low single digits) (www.ncbi.nlm.nih.gov). This suggests Intu is a housekeeping protein for ciliated cells, present wherever cells have primary cilia or require ciliary assembly during development.
During embryonic development, Intu is likely expressed in regions undergoing morphogenesis that depend on cilia-mediated signaling. In mice, Intu mRNA is present in limb bud mesenchyme (important for digit formation) and craniofacial primordia, in line with its role in patterning those structures (though specific in situ expression studies are not detailed here). Intu is also expected to be expressed in the embryonic node and neural tube floor plate, where Hedgehog signaling via cilia is active. Indeed, Intu function is cell-autonomously required in epidermal and hair follicle cells for ciliogenesis, implying it is expressed in skin progenitors during hair follicle development (pmc.ncbi.nlm.nih.gov). Similarly, its requirement in chondrocytes for normal bone growth suggests expression in the cartilage growth plate during ossification.
Regulation of INTU expression is not fully characterized, but there is some evidence that INTU levels can be altered in disease contexts. For example, in cancer, INTU has been noted to have a role: studies in basal cell carcinoma (a skin cancer driven by Hedgehog signaling) found that Intu functions synergistically with activated Hh signaling and might act as an oncogenic factor in that context (pmc.ncbi.nlm.nih.gov). Conversely, in certain cancers like lung adenocarcinoma and endometrial carcinoma, INTU expression is reportedly downregulated, possibly due to epigenetic silencing or loss of cilia in tumor cells (pmc.ncbi.nlm.nih.gov). These observations suggest that while INTU is generally expressed in normal tissues, its expression can be modulated in pathological states, particularly those involving Hh pathway activity or cilia presence.
At the protein level, Intu is likely subject to typical post-translational regulation for a ciliary protein. Some PCP/cilia proteins are regulated by phosphorylation or ubiquitination, though specific modifications on Intu have not been well documented. The Human Protein Atlas indicates Intu protein detection in ciliated structures of certain cell types, but overall, Intu is not a highly abundant protein, consistent with its specialized role in a multi-protein complex.
In summary, INTU is widely expressed in human tissues and throughout development wherever ciliated cells play roles. Its expression levels are relatively even (not extremely tissue-specific), highlighting its general necessity for cellular infrastructure (cilia). Changes in INTU expression in diseases, such as certain cancers, underscore a potential regulatory link between cilia-related genes and pathological processes. For Gene Ontology annotation, INTU would be noted as expressed in ciliated cell types across various tissues, reflecting its ubiquitous yet crucial presence.
The INTU gene is highly conserved across evolution, particularly among animals that utilize planar cell polarity and ciliogenesis. INTU was originally identified in fruit flies (Drosophila melanogaster) as the gene inturned, a PCP effector required for proper orientation of hairs on the fly wing. The human INTU gene was later recognized as the ortholog of Drosophila inturned based on sequence homology (pmc.ncbi.nlm.nih.gov). Homologs of INTU are found in other invertebrates and in nearly all ciliated vertebrates. The Intu/Fuz/Wdpcp module of PCP effectors is deeply conserved: in Drosophila, these proteins control tissue polarity, and in vertebrates, they have acquired the additional role of governing ciliogenesis (pmc.ncbi.nlm.nih.gov). For example, the mouse Intu gene (also called Pdzk6 in older nomenclature) encodes a protein 88% identical in length (940 amino acids) to human INTU, with very high sequence similarity in critical domains like the PDZ domain.
Key functional residues of Intu are preserved across species. A comparison of Intu protein sequences from vertebrates shows strong conservation, especially in the PDZ domain and C-terminal region (pmc.ncbi.nlm.nih.gov). One illustrative case: an isoleucine at position 813 of human Intu (near the C-terminus) is conserved in all examined vertebrates and is replaced by a functionally similar hydrophobic residue (phenylalanine) in Drosophila (pmc.ncbi.nlm.nih.gov). This conservation underscores that the C-terminal segment is important for Intu’s role, and that even insects share some structural features with human INTU, despite lacking primary cilia (flies use Intu only for planar polarity, not ciliogenesis).
Phylogenetic analyses classify INTU in a small family of ciliogenesis/PCP effector proteins present in chordates, arthropods, and other animal phyla. No clear homologs exist in organisms that do not form cilia (e.g., plants, fungi), highlighting Intu’s specialization for ciliated metazoans. In mammals, one can find direct one-to-one orthologs of INTU in species from primates down to fish. C. elegans (a nematode) may lack a clear inturned ortholog, correlating with differences in its planar polarity pathways or ciliary structures. However, in vertebrates like zebrafish and frog, Intu is functionally conserved: knockdown of Xenopus Intu causes ciliogenesis defects and convergent extension phenotypes, mirroring aspects seen in mice (pmc.ncbi.nlm.nih.gov). This cross-species evidence confirms that Intu’s role in cilia and development arose early and has been maintained due to strong selective pressure.
In conclusion, INTU is an evolutionarily conserved gene from flies to humans, associated with the development of multicellular polarity and ciliary organelles. Conservation of sequence and function indicates that insights from model organisms (fruit flies, frogs, mice) about Intu/INTU are applicable to human biology (pmc.ncbi.nlm.nih.gov). This evolutionary perspective is important for GO curation, as it supports the transfer of functional annotations (e.g., “cilium assembly” or “planar cell polarity”) across species based on the orthologous relationships.
Research on INTU has been fueled by genetic and cell-biological studies in multiple organisms. Below are key experimental findings that support current understanding of INTU’s function, localization, and role in disease:
Discovery in Drosophila (1990s–2000s): The inturned gene was identified in fruit flies as a planar cell polarity mutant that affects the orientation of cuticular hairs. Although this was in a context without primary cilia, it set the stage for finding mammalian Intu. Early fly studies established Intu as a PCP effector acting downstream of core PCP genes.
Role in Vertebrate Ciliogenesis (Park et al. 2006): The first indication that Intu might link to cilia came from Xenopus laevis embryos. Morpholino knockdown of Xenopus Intu (and the related protein Fuz) caused failure of ciliogenesis in multiciliated cells and defects in convergent extension movements (pmc.ncbi.nlm.nih.gov). This suggested that vertebrate Intu has a dual role in cilia formation and PCP-related morphogenesis.
Mouse Knockout Studies (Zeng et al. 2010): A seminal mouse study showed that Intu null mutants are embryonic lethal around mid-gestation, with severe ciliopathy-like defects. Mutant embryos lacked almost all primary cilia, leading to disrupted Hedgehog signaling and developmental anomalies such as polydactyly and neural tube patterning defects (pmc.ncbi.nlm.nih.gov). This provided direct evidence that Intu is essential for making cilia and that its absence mimics known ciliopathies.
Keratinocyte Differentiation and Skin (Lee et al. 2012, Cell Death Differ): Tissue-specific deletion of Intu in mouse skin demonstrated that Intu regulates hair follicle differentiation via primary cilia (pmc.ncbi.nlm.nih.gov). Intu-deficient epidermal cells were unciliated, which surprisingly did not affect general skin stratification but blocked hair follicle development, highlighting a context-specific requirement for Intu in Hh signaling during folliculogenesis.
INTU as CPLANE Complex Component (Toriyama et al. 2016, Nat. Genet.): A proteomics-driven study identified Intu as part of the CPLANE complex that also includes FUZ, WDPCP, and JBTS17 (CPLANE1) (pmc.ncbi.nlm.nih.gov). This work showed that Intu directly binds IFT-A proteins, recruiting them to basal bodies for ciliogenesis (pmc.ncbi.nlm.nih.gov). It also linked INTU mutations to human ciliopathies for the first time. Notably, Toriyama et al. described patients with compound INTU mutations presenting short-rib polydactyly syndrome, establishing INTU as a human disease gene (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov).
Linking Cilia to Actin (Yasunaga et al. 2015, J. Cell Biol.): This study in Xenopus multiciliated cells demonstrated that Intu forms a complex with NPHP4 (a ciliary base protein) and DAAM1 (an actin regulator) (pmc.ncbi.nlm.nih.gov). The data showed Intu is required to connect basal bodies to the actin cytoskeleton, affecting the dense actin meshwork needed for basal body anchoring (pmc.ncbi.nlm.nih.gov). Loss of Intu led to fragmented apical actin and mislocalized basal bodies, elucidating how Intu coordinates cytoskeletal reorganization for ciliogenesis (pmc.ncbi.nlm.nih.gov).
Human Ciliopathy Reports (2017–2021): Clinical genetic studies have reported INTU mutations in humans. Thauvin-Robinet et al. (2017) included INTU in a comprehensive analysis of Oral-Facial-Digital syndromes, and two families with OFD type XVII due to INTU were described (pubmed.ncbi.nlm.nih.gov). In 2021, Izmiryan et al. reported a third family and reviewed the INTU-related OFD17 phenotype (pubmed.ncbi.nlm.nih.gov) (pubmed.ncbi.nlm.nih.gov). These reports, along with the Nat. Genet. 2016 case, solidified INTU’s link to OFD syndrome and Jeune-type thoracic dystrophy.
Cancer-Related Findings (2018–2022): Emerging evidence connects INTU to cancer biology. For example, a study by Wong et al. (2018) found that Intu supports oncogenic Hedgehog signaling in basal cell carcinoma, as loss of Intu reduced tumor growth (implying an oncogenic role when Hh is driving cancer) (pmc.ncbi.nlm.nih.gov). Conversely, Wang et al. (2022) observed downregulation of INTU (and IFT88) in certain carcinomas, suggesting a loss of ciliary gene expression in those tumor types (pmc.ncbi.nlm.nih.gov). These findings open new areas of research into INTU’s role beyond developmental disorders, possibly in cilia-related aspects of cancer cell behavior.
Key Literature for GO Annotations: The evidence above can directly inform Gene Ontology annotations. For instance, Park et al. 2006 and Zeng et al. 2010 support annotating INTU with cilium assembly (GO:0060271) and Hedgehog signaling processes. Yasunaga et al. 2015 provides evidence for actin cytoskeleton organization and ciliary basal body localization GO terms. Toriyama et al. 2016 underpins GO annotations for intraflagellar transport and ciliary membrane components, as well as disease ontology links. The human genetic studies justify annotating INTU in the context of orofaciodigital syndrome (OFD17) and skeletal dysplasia. Curators can refer to these primary sources (and their PubMed IDs) for high-confidence, traceable assertions about INTU’s biological roles (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov) (pubmed.ncbi.nlm.nih.gov). Each of these studies contributes to a comprehensive picture that INTU is a conserved ciliary protein essential for proper cell signaling, structure, and development.