PQBP1 Affects Lipid Storage Figure 5. Generation of T21D12.3 -specific and T07A9.1 -specific mutant nematodes. A) T21D12.3 is the strictly conserved homologue of mammalian PQBP1 possessing WW domain and C-terminal domain. The genome maps show deleted regions in the genome of T21D12.3 and T07A9.1 mutants. B) T07A9.1 possesses a homology only to C-terminal domain of PQBP1 and does not possess WW domain. The genome maps show deleted regions in the genome of T07A9.1 mutants. doi:10.1371/journal.pone.0004104.g005 A hypothesis to account for the change of lipid granules would be that PQBP1 regulates expression of Fsp27/CIDE-C, which locates at lipid droplets and influences their size [23], like PPAR-c regulates Fsp27 [24]. CIDE-A, another lipid droplet-associated protein controlling triglyceride deposition in white adipocytes [25] might be another target of transcriptional control by PQBP1. Though we have obtained preliminary data to support the hypothesis (data not shown), these issues would be the next project regarding the lipid metabolism function of PQBP1. PQBP1 expression in neurons of C. elegans In this study, we focused on the lipid metabolism, and have not analyzed neuronal functions of the nematode homologue of PQBP1. However, in mammals, PQBP1 definitely functions in neurons and/or progenitor cells, and the neuronal functions are essential for understanding MR symptoms found in PQBP1- mutated patients. Here, we found that pqbp-1.1 was expressed in head ganglion cells at L1 stage (Fig. 3A), which may correspond to neural progenitor cells in mammals. Although our preliminary observation showed no remarkable decline of locomotive activity, further analysis is needed for definite evaluation and it is essential for understanding T21D12.3 function in learning and memory functions in C. elegans. Meanwhile, analysis of PQBP1 functions in neurons are now undergoing in our laboratory with Drosophila mutants and mammalian neural stem cells. Drosophila mutants show a unique type of learning impairment (unpublished observation), which is different from the long-term memory disturbance observed in transgenic fly overexpressing human PQBP1 [26]. These experiments using various animal models will promote understanding of the whole scheme of PQBP1 diseases and might lead to certain insights into basic biology in the future. Human patients with mutations of the PQBP1 gene show mental retardation and microcephaly as major symptoms. However, PQBP1 is expressed widely in multiple tissues of mammals. Therefore, if different animal models have different advantages for analyzing multiple molecular functions of a gene, we should better take the merit. We should employ appropriate animal models for appropriate functional analyses. In this study, we took advantage of the nematode model for analyzing the phenotype in lipid metabolism. We have already constructed conditional knock out mice and RNAi-mediated knock down mice as well as fly models for analyzing neuronal functions of PQBP1, which will be reported elsewhere. The ‘‘lean body’’ is not a tiny symptom because the research on this symptom might link to cell metabolism and the related PLoS ONE | www.plosone.org 5 January 2009 | Volume 4 | Issue 1 | e4104