Neuroligin dependence of social behaviour inC. elegansprovides a model to investigate an autism associated gene

Abstract

9Autism spectrum disorder (ASD) is characterised by a triad of behavioural impairments 10 including social behaviour. Neuroligin, a trans-synaptic adhesion molecule, has emerged as a 11 penetrant genetic determinant of behavioural traits that signature the neuroatypical 12 behaviours of autism. However, the function of neuroligin in social circuitry and the impact 13 of genetic variation to this gene is not fully understood. Indeed, in animal studies designed 14 to model autism there remains controversy regarding the role of neuroligin dysfunction in 15 the expression of disrupted social behaviours. The model organism, C. elegans, offers an 16 informative experimental platform to investigate the impact of genetic variants on social 17 behaviour. In a number of paradigms it has been shown that inter-organismal 18 communication by chemical cues regulates C. elegans social behaviour. We utilise this social 19 behaviour to investigate the effect of autism associated genetic variants within the social 20 domain of the research domain criteria. We have identified neuroligin as an important 21 regulator of social behaviour and segregate the importance of this gene to the recognition 22and/or processing of social cues. We also use CRISPR/Cas9 to edit an R-C mutation that 23 mimics a highly penetrant human mutation associated with autism. C. elegans carrying this 24 mutation phenocopy the behavioural dysfunction of a C. elegans neuroligin null mutant, 25 thus confirming its significance in the regulation of animal social biology. This highlights that 26 quantitative behaviour and precision genetic intervention can be used to manipulate 27 discrete social circuits of the worm to provide further insight to complex social behaviour. 28

Investigating autism associated genes inC. elegansreveals candidates with a role in social behaviour

“…The analysis of single, high penetrant, variants is becoming increasingly well refined with the use of animal social behaviours. Use of social behaviours underpinned by discreet neural circuits has helped establish the role of some ASD associated genes in the social domain [39, 86]. However, the analysis of common, low penetrant, variants is more complex.…”

“…C. elegans have been used in targeted single gene approaches and in screens of ASD associated genes to provide valuable insight into the role of some genes in sensory processing, development and learning phenotypes [36, 87]. Recently we have shown the utility of using a social behavioural paradigm in C. elegans to investigate a single ASD associated gene [39]. This paradigm is based on inter-organismal signalling by use of chemosensory social cues which results in a progeny-induced food leaving phenotype [38].…”

“…In conclusion, investigation of ASD associated orthologues in C. elegans identified genes from a number of candidates implicated in ASD that disrupt social behaviour in the worm. Identification of these genes highlights how this assay might be used in quantitative approaches that can probe the single [39] and polygenic nature of ASD and its underpinning genetic architecture [36]. The robust nature of this assay provokes a better detailing of the cellular and circuit dependence of this social interaction.…”

“…In all food leaving assays the number of food leaving events were counted manually during a 30 minute observation period using a binocular dissecting microscope (Nikon SMZ800; X10). A food leaving event was defined as when the whole of the worm’s body came off the bacterial food lawn, as previously described [39]. Following each food leaving assay the % proportion of eggs, L1 and L2 progeny on the plate was calculated.…”

“…This progeny-dependent food leaving behaviour is the result of inter-organismal communication and is thought to be underpinned by a novel social circuit [38]. The utility of this social paradigm to probe autism related dysfunction was demonstrated by showing that when a penetrant mutation of human neuroligin is introduced into the worm orthologue, nlg-1 , it results in disrupted progeny induced food leaving behaviour [39].…”