Social interactions, learning experiences and responses to wide-ranging environmental stimuli occur through nervous cells via synapses. Several observations have suggested that the alteration of neuron connections during nervous system development could represent the root of many cases of autism spectrum disorder. Neuroligins are synaptic cell adhesion proteins that have been shown to be able to induce synaptogenesis. Single missense and frameshift mutations in neuroligin coding genes have been proposed that may lead to autism or mental retardation with complete penetrance (Baudouin and Scheiffele, 2010; Etherton et al., 2011). In C. elegans, nlg-1 is orthologous to mammal neuroligin genes, and it has been shown that nlg-1 mutants are defective in several sensory behaviors and sensitive to oxidative stress (Calahorro et al., 2009; Hunter et al., 2010).

We report here that transgenic expression of rat Nlgn1 and human NLGN1 proteins are functional in C. elegans. The wild type behavior pattern was rescued in nlg-1 deficient mutants by expressing cDNAs from rat Nlgn1 or human NLGN1 genes under C. elegans nlg-1 promoter (Figure 1A). Induced changes Asp396Stop in human NLGN1 or Arg453Cys in worm NLG1 proteins, failed to rescue the wild type phenotype (Figure 1B). These results indicate that mammalian and C. elegans neuroligins seem to be functionally comparable. The results anticipate that the nematode could be useful as an in vivo model for studying specific synapse mechanisms involved in autism. This system will allow the analysis of how mutations in neuroligin genes change phenotypes in different C. elegans genetic backgrounds and the study of their interactions with different environmental factors. It is probable also that this approach could be extended to other genes encoding synaptic proteins implicated in autism spectrum disorder, such as neurexins and shanks.

Table 1. Strains used in this study

Name Genotype Reference/Source
N2 wild type reference CGCa
VC228 nlg-1 (ok259) X CGCa
CRR1b nlg-1 (ok259) X This study
CRR100 nlg-1 (ok259) X; crrEx4 [pPD95.77; pDD04 NeoR (pmyo-2::GFP)] This study
CRR104c nlg-1 (ok259) X; crrEx4 [pPD95.77 (Pnlg-1::nlg-1); pDD04NeoR (pmyo-2::GFP)] This study
CRR105 nlg-1 (ok259) X; crrEx5 [pPD95.77 (Pnlg-1::nlg-1-R437C); pDD04NeoR (pmyo-2::GFP)] This study
CRR106d nlg-1 (ok259) X; crrEx6 [pPD95.77 (Pnlg-1::NLGN1); Pnrx-1::GFP] This study
CRR107 nlg-1 (ok259) X; crrEx7 [pPD95.77 (Pnlg-1::NLGN1-R453C); pDD04NeoR (pmyo-2::GFP)] This study
CRR108 nlg-1 (ok259) X; crrEx8 [pPD95.77 (Pnlg-1::NLGN1-D396X); pDD04NeoR (pmyo-2::GFP)] This study
CRR109e nlg-1 (ok259) X; crrEx9 [pPD95.77 (Pnlg-1::Nlgn1::EGFP); pBCN24NeoR] This study

a Caenorhabditis Genetics Center.

b Obtained by outcrossing VC228 strain with N2 six times.

cThe cDNA nlg-1 coding region was obtained from clone yk1657a10, Yuji Kohara, National Institute of Genetics, Mishima, Japan.

dThe cDNA human NLGN1 coding region was obtained from clone KIAA1070 (hj05602), Kazusa DNA Research Institute, Japan.

e Rat Nlgn-1::EGFP was a gift from Dr. Thomas Dresbach, Univ. Göttingen, Germany.