Nematode Homologue of PQBP1, a Mental Retardation Causative Gene, Is Involved in Lipid Metabolism Keiko Takahashi1,2, Sawako Yoshina2, Maekawa Masashi3, Wakana Ito1, Takao Inoue3, Hiroki Shiwaku 1 , Hiroyuki Arai3, Shohei Mitani2, Hitoshi Okazawa 1 * 1 Department of Neuropathology, Medical Research Institute, Tokyo Medical and Dental University, Tokyo, Japan, 2 Department of Physiology, Tokyo Women’s Medical University School of Medicine, Tokyo, Japan, 3 Department of Health Chemistry, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, Japan Abstract Background: PQBP1 is a causative gene for X-linked mental retardation (MR) whose patients frequently show lean body. C. elegans has a strictly conserved homologue gene of PQBP1, T21D12.3. Methodology and Principal Findings: We generated Venus-transgenic and T21D12.3-mutant nematodes to analyze developmental expression patterns and in vivo functions of the nematode PQBP1 homologue protein (pqbp-1.1). During development, pqbp-1.1 is expressed from cell proliferation stage to larva stage. In larva, intestinal cells show the highest expression of pqbp-1.1, while it decreases in adult worms. The mutants of pqbp-1.1 show a decrease of the lipid content in intestinal cells. Especially, incorporation of fatty acid into triglyceride is impaired. ShRNA-mediated repression of PQBP1 also leads to reduction of lipid content in mammalian primary white adipocytes. Conclusion/ Significance: These results suggest that pqbp-1.1 is involved in lipid metabolism of intestinal cells. Dysfunction of lipid metabolism might underlie lean body, one of the most frequent symptoms associating with PQBP1-linked MR patients. Citation: Takahashi K, Yoshina S, Masashi M, Ito W, Inoue T, et al. (2009) Nematode Homologue of PQBP1, a Mental Retardation Causative Gene, Is Involved in Lipid Metabolism. PLoS ONE 4(1): e4104. doi:10.1371/journal.pone.0004104 Editor: Sotirios Koutsopoulos, Massachusetts Institute of Technology, United States of America Received August 14, 2008; Accepted December 3, 2008; Published January 1, 2009 Copyright: 2009 Takahashi et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by grants to H.O. from Japan Science Technology Agency (PRESTO, JST, Japan) and from Ministry of Education, Culture, Sports, Science and Technology of Japan (16390249, 16650076, 18390254, 18650097, Research on Pathomechanisms of Brain Disorders: 17025017, 18023014, 20023011). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: okazawa-tky@umin.ac.jp Introduction PQBP1 was identified as a binding protein to the polyglutamine (polyQ) tract of the causative gene products of a major group of neurodegeneration, polyglutamine diseases [1]. PQBP1 includes two protein interaction domains: WW domain (WWD) through which PQBP1 interacts with RNA polymerase II and NpwBP [2,3] and C-terminal domain (CTD) through which it interacts with a splicing factor, U5-15kD [4,5]. Subsequently, PQBP1 was identified as a causative gene for a group of mental retardation including Renpenning syndrome, Golabi-Ito-Hall and the Suther- land-Haan syndromes as well as non-symptomatic X-linked mental retardation with no anomaly [6–8]. The frequency of these PQBP1-linked disorders is relatively high [9]. Among various associating symptoms, one of the most frequent symptoms in these patients is lean body, which is found in 87% of the patients [10]. In this study, we investigated expression patterns of nematode homologue of PQBP1 (pqbp-1.1) during development, and generated mutants of T21D12.3. We found that pqbp-1.1 is expressed in intestinal cells storing lipid in nematodes and that the mutant of T21D12.3 shows reduction of lipid storage in intestinal cells although intestinal cells did not reduce in their number. Furthermore, we found shRNA-mediated knocking down of PQBP1 leads to reduction of lipid storage in mouse primary white adipocytes. These results suggest that PQBP1 is involved in lipid metabolism beyond species and that dysfunction of lipid metabolism might be a cause of lean body in human PQBP1 mutations. Results PQBP1 homologue is expressed in intestinal cells C. elegans possesses a homologue gene of PQBP1, T21D12.3, which encodes a protein (pqbp-1.1) containing both of the essential protein interacting domains, WWD and CTD [11]. Amino acid identities between human and nematode PQBP1 are 35% in the whole molecule, 52% in WWD and 55% in CTD. To analyze expression patterns of T21D12.3, the PQBP1 homologue in C. elegans, we constructed a reporter plasmid expressing a fluorescent fusion protein of pqbp-1.1 and Venus, a variant of yellow fluorescent protein with fast and efficient maturation for visualization [12] under the control of T21D12.3 enhancer/ promoter according to the method described previously [13]. Endogenously, T21D12.3 and T21D12.4 (pat-6) are regulated as an operon (Fig. 1). Therefore, we constructed a plasmid that contains 6.7 kb genome DNA from the 2.7 kb upstream of the neighboring gene (pat-6) to the 39 end of T21D12.3 (Fig. 1). Thereafter, Venus cDNA was subcloned into exon 4 of T21D12.3 to express a nematode PQBP1-Venus fusion protein (pqbp-1.1-Venus). PLoS ONE | www.plosone.org 1 January 2009 | Volume 4 | Issue 1 | e4104