We identified one such protein in a yeast two-hybrid screen, using as bait the peripheral Golgi phosphatidylinositol(4,5)P2 5-phosphatase OCRL1 that is implicated in a human disease, the oculocerebrorenal syndrome.
The large majority of the OCRL1 mutations producing Lowe syndrome are either missense mutations localized mainly in the catalytic domain or non-sense/frameshift mutations resulting in truncated proteins.
These studies substantiate the first mouse model of Lowe syndrome and give insights into the role of OCRL in cellular trafficking of multiligand receptors.
Altogether, we describe here differential phenotypes between fibroblasts from Lowe and Dent-2 patients, both associated with OCRL LOF mutations, we exclude direct roles of PI(4,5)P2 and INPP5B in this phenotypic variability and we underline potential key alterations leading to ocular and neurological clinical features in Lowe syndrome.
The renal phenotype of 16 patients with Lowe syndrome (10.9 +/- 7.0 yr) under care of the authors was characterized to define overlap of symptoms with Dent disease and infer clues about OCRL function.
Full chromosome studies in the parents and the proband and mutation analysis on peripheral blood lymphocytes (and on skin cultured fibroblasts from affected and unaffected skin areas in the child) in the genes for subcortical band heterotopia (DCX (Xq22.3-q23)], lissencephaly (PAFAH1B1, alias LIS1, at 17p13.3), and oculocerebrorenal syndrome of Lowe (OCRL at Xq23-q24)] were unrevealing.
Cumulatively, our data provide evidence for a role of OCRL in cilia maintenance and suggest the involvement of ciliary dysfunction in the manifestation of Lowe syndrome.
Mutations in the inositol 5-phosphatase OCRL are responsible for Lowe syndrome, an X-linked disorder characterized by bilateral cataracts, mental retardation, neonatal hypotonia, and renal Fanconi syndrome, and for Dent disease, another X-linked condition characterized by kidney reabsorption defects.
We discuss how studies of OCRL have led to important discoveries about the basic mechanisms of membrane trafficking and describe the key features and limitations of the currently available animal models of Lowe syndrome.
Moreover, loss of OCRL1 RhoGAP and the resulting alteration in Rho pathways may contribute to mental retardation in Lowe syndrome, as illustrated in other forms of X-linked mental retardation.
Our findings confirm that OCRL1 is involved in the functional defects characteristic of Dent's disease and suggest that patients carrying missense mutations in exons where many Lowe mutations are mapped may represent a phenotypic variant of Lowe syndrome.
Mutations in the OCRL1 gene, which encodes ocrl1, a phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P(2)) 5-phosphatase, are the cause of Lowe syndrome.
Taking into consideration the relevance of the signaling pathways hosted by the primary cilium, our results suggest hitherto unrecognized mechanisms by which Ocrl1 deficiency may contribute to the phenotypic characteristics of LS.