Reptin/Ruvbl2 is a Lrrc6/Seahorse interactor essential for cilia motility

Abstract

Primary ciliary dyskinesia (PCD) is an autosomal recessive disease caused by defective cilia motility. The identified PCD genes account for about half of PCD incidences and the underlying mechanisms remain poorly understood. We demonstrate that Reptin/ Ruvbl2, a protein known to be involved in epigenetic and transcriptional regulation, is essential for cilia motility in zebrafish. We further show that Reptin directly interacts with the PCD protein Lrrc6/Seahorse and this interaction is critical for the in vivo function of Lrrc6/Seahorse in zebrafish. Moreover, whereas the expression levels of multiple dynein arm components remain unchanged or become elevated, the density of axonemal dynein arms is reduced in reptin hi2394 mutants. Furthermore, Reptin is highly enriched in the cytosol and colocalizes with Lrrc6/Seahorse. Combined, these results suggest that the Reptin-Lrrc6/Seahorse complex is involved in dynein arm formation. We also show that although the DNA damage response is induced in reptin hi2394 mutants, it remains unchanged in cilia biogenesis mutants and lrrc6/seahorse mutants, suggesting that increased DNA damage response is not intrinsic to ciliary defects and that in vertebrate development, Reptin functions in multiple processes, both cilia specific and cilia independent.ciliopathy | chromatin remodeling complex | dynein arm assembly factor A lthough the sensory function of the cilium has garnered significant attention only in the past decade, defective cilia motility was recognized nearly four decades ago as the cause of primary (genetic) ciliary dyskinesia (PCD) (1). PCD is a group of rare human genetic diseases characterized by recurrent infections of the respiratory system, male infertility, and frequently laterality defects, all of which are tightly linked to cilia motility abnormalities. Up to now, 19 PCD genes have been identified (2-20). However, combined they account for about 50% of all PCD cases, suggesting the existence of multiple additional causative genes. Despite such significant advances, our understanding of how cilia motility is regulated is limited and the list of genes involved in cilia motility remains incomplete.In motile cilia or flagella, dynein arms are large protein complexes powering cilia motility. Not surprisingly, multiple PCD genes encode dynein arm components, including DNAL1, DNAI1, DNAI2, DNAH5, and DNAH11 (2-6). In addition, it is understood that dynein arm subunits are preassembled in the cytosol, transported into cilia/flagellum, and docked onto the axoneme, although the underlying mechanisms are poorly understood (21). In recent years, three PCD genes, i.e., DNAAF1/LRRC50 (7, 8), DNAAF2/ KTU (9), and DNAAF3/PF22 (10) have been shown to be involved in the assembly of dynein arm subunits, highlighting the relevance and importance of this process in cilia motility and PCD.Very recently, mutations in human LRRC6/SEAHORSE were linked to PCD (18). Similar to the three known dynein arm assembly factors, mutations in LRRC6/SEAHORSE lead to the absence of both the outer...

NudC regulates actin dynamics and ciliogenesis by stabilizing cofilin 1

“…Cilia have been demonstrated to be involved in various developmental processes in vertebrates [5,11,23,24]; therefore, we explored the function of NudC during zebrafish development. Zebrafish NudC shares high homology with human NudC (identity, 72.0%; similarity, 85.0%) and the polyclonal antibodies against human NudC also recognized zebrafish NudC ( Figure 3A).…”

“…As it has been reported that the motile cilia in pronephric ducts are crucial for fluid flow [5,11,23], we examined whether NudC influences the cilia in pronephric ducts. Immunostaining showed that NudC depletion caused longer cilia in anterior pronephric ducts of NudC morphants, which was reversed by exogenous expression of NudC mRNA ( Figure 3L).…”

“…Motile cilia often occur in epithelial tissues to generate fluid flow, while non-motile cilia are distributed widely and are considered critical for extracellular signal reception and transduction [1,2]. Cilia play essential roles in vertebrate development, including establishment of left-right asymmetry, and brain and kidney development [3][4][5]. Disruption of cilia structure or motility is associated with a range of human disorders termed ciliopathies, such as primary ciliary dyskinesias, cystic kidney diseases and situs inversus [6][7][8][9].…”

The Oligomeric Outer Dynein Arm Assembly Factor CCDC103 Is Tightly Integrated within the Ciliary Axoneme and Exhibits Periodic Binding to Microtubules

“…The RPAP3_C domain has a very limited distribution, and, intriguingly, all proteins in which it has been found (CCDC103, RNA polymerase II-associated protein 3, and SPAG1) are either directly involved in ciliary assembly (CCDC103 (19) and SPAG1 (31)) or, in the case of RPAP3, interact with proteins (reptin (35) and WDR92 3 ) required for this process. Using various truncated recombinant forms and fusion proteins containing the coiled coil segments, we determined that intermonomer associations and microtubule binding involve the central region containing the RPAP3_C domain and that the coiled coils do not appear to form either homo-or heterodimers.…”

Left-right asymmetry: lessons from Cancún

“…Magdalena Cardenas-Rodriguez (from Jose Badano's group, Institut Pasteur de Montevideo, Uruguay) discussed how the Ccdc28b protein controls cilia length through interactions with components of mTOR complex 2 (mTORC2) (CardenasRodriguez et al, 2013). Zhaoxia Sun (Yale University, New Haven, USA) showed that loss of the reptin protein in fish led to cilia with reduced dynein arms and aberrant motility resulting in LR defects (Zhao et al, 2013). Among the novel mouse mutants that Cecilia Lo updated us on was an allele of dynein with defects only in ciliary beat frequency.…”