PKG and the neural basis for behavioral phenotypes

Increased expression of a cGMP-dependent protein kinase in rotation-adapted western corn rootworm (Diabrotica virgifera virgifera L.)

A new 'variant' behavior in western corn rootworm (WCR) has resulted in egg-laying into non-cornfields, compared to 'normal' deposition of eggs in cornfields, allowing these insects to circumvent crop rotation. No morphological or genetic characteristics have been defined to differentiate between the normal and variant biotypes. Cyclic GMP-dependent protein kinases (PKG) have been implicated in the regulation of behaviors in vertebrates, insects, and nematodes, including foraging behavior in Drosophila. A cDNA with homology to the Drosophila melanogaster foraging gene (called Dvfor1) was cloned from WCR. The deduced DvFOR1 protein is approximately 70% similar to FOR proteins in Drosophila, silkworm (Bombyx mori) and honeybee (Apis mellifera). It contains a coiled-coil region, two tandem cyclic nucleotide-binding domains, a serine/threonine kinase catalytic domain, and a serine/threonine kinase catalytic domain extension, which are all characteristically found in PKG proteins. Real-time PCR assays of foraging transcript levels in heads of normal and rotation adapted females of WCR obtained from lab-reared insect colonies indicated that the variants had higher levels (25%) of PKG expression than normals. The magnitude of this increase is similar to that observed in Drosophila rover phenotypes compared to sitter phenotypes. However, Diabrotica contains at least two different foraging gene transcripts, which complicates establishing a direct link between the level of gene expression and insect behavior.

Visual pattern memory requires foraging function in the central complex of Drosophila

The role of the foraging (for) gene, which encodes a cyclic guanosine-3',5'-monophosphate (cGMP)-dependent protein kinase (PKG), in food-search behavior in Drosophila has been intensively studied. However, its functions in other complex behaviors have not been well-characterized. Here, we show experimentally in Drosophila that the for gene is required in the operant visual learning paradigm. Visual pattern memory was normal in a natural variant rover (for(R)) but was impaired in another natural variant sitter (for(S)), which has a lower PKG level. Memory defects in for(S) flies could be rescued by either constitutive or adult-limited expression of for in the fan-shaped body. Interestingly, we showed that such rescue also occurred when for was expressed in the ellipsoid body. Additionally, expression of for in the fifth layer of the fan-shaped body restored sufficient memory for the pattern parameter "elevation" but not for "contour orientation," whereas expression of for in the ellipsoid body restored sufficient memory for both parameters. Our study defines a Drosophila model for further understanding the role of cGMP-PKG signaling in associative learning/memory and the neural circuit underlying this for-dependent visual pattern memory.

Lack of association between polymorphism of the human cyclic GMP-dependent protein kinase gene and obesity

OBJECTIVE

To investigate whether genetic variation in the cyclic GMP-dependent protein kinase gene (PRKG1) is associated with obesity.

METHODS

The study included 143 individuals from New York City area, NY, USA. The subjects were sampled on the basis of body mass index (BMI): obese (BMI ranging from 33.8 to 89.5 kg/m(2)), and nonobese (BMI ranging from 16.0 to 29.4 kg/m(2)). The association between C2276T polymorphism in PRKG1 gene and obesity was tested using linear regression analysis.

RESULTS

BMI levels were predicted by linear regression models adjusted for demographic factors. An analysis was performed twice: in individuals of all ethnic backgrounds and in European-Americans only. In both cases, genotype did not have a significant effect.

CONCLUSION

We found no evidence that the C2276T polymorphism in the PKRG1 gene is associated with obesity.

Importance of NO/cGMP signalling via cGMP-dependent protein kinase II for controlling emotionality and neurobehavioural effects of alcohol

Cyclic GMP is a second messenger for nitric oxide (NO) that acts as a mediator for many different physiological functions. The cGMP-dependent protein kinases (cGKs) mediate cellular signalling induced by NO and cGMP. Here, we explored the localization of cGMP-dependent protein kinase type II (cGKII) in the mouse brain. In situ hybridization revealed high levels of cGKII mRNA in cerebral cortex, thalamic nuclei, hypothalamic nuclei, and in several basal forebrain regions including medial septum, striatum and amygdala. The close link to NO and the distribution pattern of cGKII suggested that this enzyme might be involved in emotional reactions and responses to drugs of abuse. Therefore, cGKII knockout animals (cGKII-/-) were compared with littermate controls in behavioural tests (i) for emotion-linked and (ii) for acute and chronic ethanol responses. Deletion of cGKII did not influence aggressive behaviour but led to enhanced anxiety-like behaviour. In terms of acute responses to ethanol, cGKII-/- mice were hyposensitive to hypnotic doses of ethanol as measured by the loss of righting reflex, without an alteration in their blood alcohol elimination. In a two-bottle free choice test, cGKII-/- mice showed elevated alcohol consumption. No taste differences to sweet solutions were observed compared to control animals. In summary, our data show that cGKII activity modulates anxiety-like behaviour and neurobehavioural effects of alcohol.