Swordtails turn off when turned on

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Female swordtails down regulate, or turn off, certain genes and up regulate, or turn on, others when interacting with male fish, according to a recent study by scientists from the USA.

The study conducted by Molly Cummings, Jonah Larkins-Ford, Christian Reilly, Ryan Wong, Mary Ramsey and Hans Hofmann, is to be published in the Proceedings of the Royal Society B: Biological Sciences.

The authors recorded behavioural responses of female swordfishes (Xiphophorus helleri) exposed (only visually) to : (1) a pair of males of differing attractiveness (one large & one small male), (2) two females, (3) two unattractive males, and (4) two empty compartments.

This was followed by whole brain gene expression profiling (using gene array technology) and real time quantitative PCR.

The profiling identified possible candidate genes for specific social conditions, and the quantitative PCR examined the relationship between behaviour and the levels of candidate gene expression.

The authors identified 306 out of 3422 genes that were analysed that showed differential expression in all four experimental conditions.

Hierarchical clustering of the 306 differentially expressed genes among the four experimental conditions highlights that the greatest difference in genomic expression was between distinct classes of social stimuli (e.g. females versus attractive males) rather than presence versus absence of stimuli (e.g. attractive males versus no stimuli).

Compared to the other conditions, more genes showed reduced expression than increased expression in females exposed to attractive males; the opposite pattern was produced when females were exposed to other females.

When we examined these genes more closely, we found that distinct social conditions produce diametrically opposed patterns of gene regulation: genes that show decreased activity in the presence of large males are the same genes that are activated in the presence of females, and vice versa.

Females responding to attractive males were found to differentially express 77 genes, among which were the six candidate genes (neuroserpin, neuroligin 3, importin, apyrase, b1-andrenergic receptor and egr-1) whose expression levels were studied by the authors.

A significant relationship between five of the candidate genes (neuroserpin, neuroligin 3, importin, apyrase and egr-1) was found between their differential expression and preference behaviour specific to male-only environments.

For more information, see the paper: Cummings, ME, J Larkins-Ford, CRL Reilly, RY Wong, M Ramsey and HA Hofmann (2008) Sexual and social stimuli elicit rapid and contrasting genomic responses. Proceedings of the Royal Society B:Biological Sciences. DOI:10.1098/rspb.2007.1454.