Novel regulators of planar cell polarity: a genetic analysis in Drosophila.

Planar cell polarity (PCP) is a common feature of many epithelia and epithelial organs. Although progress has been made in the dissection of molecular mechanisms regulating PCP, many questions remain. Here we describe a screen to identify novel PCP regulators in Drosophila. We employed mild gain-of-function (GOF) phenotypes of two cytoplasmic Frizzled (Fz)/PCP core components, Diego (Dgo) and Prickle (Pk), and screened these against the DrosDel genome-wide deficiency collection for dominant modifiers. Positive genomic regions were rescreened and narrowed down with smaller overlapping deficiencies from the Exelixis collection and RNAi-mediated knockdown applied to individual genes. This approach isolated new regulators of PCP, which were confirmed with loss-of-function analyses displaying PCP defects in the eye and/or wing. Furthermore, knockdown of a subset was also sensitive to dgo dosage or dominantly modified a dishevelled (dsh) GOF phenotype, supporting a role in Fz/PCP-mediated polarity establishment. Among the new "PCP" genes we identified several kinases, enzymes required for lipid modification, scaffolding proteins, and genes involved in substrate modification and/or degradation. Interestingly, one of them is a member of the Meckel-Gruber syndrome factors, associated with human ciliopathies, suggesting an important role for cell polarity in nonciliated cells.

Modifying behavioral phenotypes in Fmr1KO mice: genetic background differences reveal autistic-like responses.

Fragile X syndrome (FXS) is the most common inherited form of intellectual disability in humans. In addition to cognitive impairment, patients may exhibit hyperactivity, attention deficits, social difficulties and anxiety, and autistic-like behaviors. The degree to which patients display these behaviors varies considerably and is influenced by family history, suggesting that genetic modifiers play a role in the expression of behaviors in FXS. Several studies have examined behavior in a mouse model of FXS in which the Fmr1 gene has been ablated. Most of those studies were done in Fmr1 knockout mice on a pure C57BL/6 or FVB strain background. To gain a better understanding of the effects of genetic background on behaviors resulting from the loss of Fmr1 gene expression, we generated F1 hybrid lines from female Fmr1 heterozygous mice on a pure C57BL/6J background bred with male Fmr1 wild-type (WT) mice of various background strains (A/J, DBA/2J, FVB/NJ, 129S1/SvImJ and CD-1). Male Fmr1 knockout and WT littermates from each line were examined in an extensive behavioral test battery. Results clearly indicate that multiple behavioral responses are dependent on genetic background, including autistic-like traits that are present on limited genetic backgrounds. This approach has allowed us to identify improved models for different behavioral symptoms present in FXS including autistic-like traits.

Exaggerated behavioral phenotypes in Fmr1/Fxr2 double knockout mice reveal a functional genetic interaction between Fragile X-related proteins.

Individuals affected by Fragile X syndrome (FXS) experience cognitive impairment, hyperactivity, attention deficits, social anxiety and autistic-like behaviors. FXS results from the loss of expression of the Fragile X mental retardation (FMR1) gene, whose protein product FMRP is thought to play an important role in neuronal function and synaptic plasticity. Two paralogs of FMRP, FXR1P and FXR2P, have been identified, forming the Fragile X-related (FXR) family of proteins. Although the functions of FXR1P and FXR2P are not well understood, there are similarities among all three FXR proteins in gene structure, amino acid sequence, expression pattern and cellular functions. Mouse models have been described for loss of Fmrp, Fxr1p and Fxr2p, the mouse homologs of FMRP, FXR1P and FXR2P. In earlier studies, we found that Fmr1 knockout (KO) mice, which do not express Fmrp, and Fxr2 KO mice, which do not express Fxr2p, show similarities in some behavioral responses such as hyperactivity. To better understand the functional relationship between FMRP and FXR2P, we generated Fmr1 KO, Fxr2 KO, Fmr1/Fxr2 double KO and wild-type control mice as littermates on the same genetic background and examined them in several behavioral assays. Results show that Fmr1/Fxr2 double KO mice have exaggerated behavioral phenotypes in open-field activity, prepulse inhibition of acoustic startle response and contextual fear conditioning when compared with Fmr1 KO mice, Fxr2 KO mice or wild-type littermates. Our findings suggest that Fmr1 and Fxr2 genes contribute in a cooperative manner to pathways controlling locomotor activity, sensorimotor gating and cognitive processes.