Abstract
The alternatively spliced trimeric G-protein subunit XLαs, which is involved in cAMP signalling, is encoded by the Gnasxl transcript of the imprinted Gnas locus. XLαs deficient mice show neonatal feeding problems, leanness, inertia and a high mortality rate. Mutants that survive to weaning age develop into healthy and fertile adults, which remain lean despite elevated food intake. The adult metabolic phenotype can be attributed to increased energy expenditure, which appears to be caused by elevated sympathetic nervous system activity. To better understand the changing phenotype of Gnasxl deficient mice, we compared XLαs expression in neonatal versus adult tissues, analysed its co-localisation with neural markers and characterised changes in the nutrient-sensing mTOR1-S6K pathway in the hypothalamus. Using a newly generated conditional Gnasxl lacZ gene trap line and immunohistochemistry we identified various types of muscle, including smooth muscle cells of blood vessels, as the major peripheral sites of expression in neonates. Expression in all muscle tissues was silenced in adults. While Gnasxl expression in the central nervous system was also developmentally silenced in some midbrain nuclei, it was upregulated in the preoptic area, the medial amygdala, several hypothalamic nuclei (e.g. arcuate, dorsomedial, lateral and paraventricular nuclei) and the nucleus of the solitary tract. Furthermore, expression was detected in the ventral medulla as well as in motoneurons and a subset of sympathetic preganglionic neurons of the spinal cord. In the arcuate nucleus of Gnasxl-deficient mice we found reduced activity of the nutrient sensing mTOR1-S6K signalling pathway, which concurs with their metabolic status. The expression in these brain regions and the hypermetabolic phenotype of adult Gnasxl-deficient mice imply an inhibitory function of XLαs in energy expenditure and sympathetic outflow. By contrast, the neonatal phenotype of mutant mice appears to be due to a transient role of XLαs in muscle tissues.
Highlights
In mammals the paternally and maternally inherited genomes contribute unequally to the development of offspring [1,2], which can be attributed to epigenetic modifications that are established in the two parental germlines
We identified several developmental changes in the central nervous system (CNS) expression pattern, and detected XLas in areas implicated in the regulation of energy homeostasis and sympathetic outflow
We employed a gene trap strategy to generate a conditionally targeted allele of Gnasxl, since a standard approach of flanking the single Gnasxl specific 59-exon with loxP sites would most likely result in disturbance of the Nespas imprinting control region (ICR) with consequences for the expression of other transcripts of the locus (Figure 1) [33]
Summary
In mammals the paternally and maternally inherited genomes contribute unequally to the development of offspring [1,2], which can be attributed to epigenetic modifications that are established in the two parental germlines. To gain insights into the causes of the developmentally changing phenotype of Gnasxl-deficient mice, we systematically analysed its expression pattern in the CNS and in peripheral tissues at neonatal and adult stages.
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