Without changing the underlying genetic sequence, environmental factors can influence how an individual’s genetic information affects their physical appearance. This can happen when specific molecular changes occur that either increase or silence the expression of certain genes. These so-called epigenetic changes can help explain why one population of mice, with the same genetic makeup, can present as two populations of either lean or obese individuals when consuming the same diet. Studies suggest that the Neuronatin (Nnat) gene may be regulated in this manner, and in a recent study by Ciminoet and colleagues, researchers set out to better understand the specific effect that this gene has on food intake and body mass. In this study LC-MS/MS was used to study the peptides of pancreatic hormones in Nnat deficient and wildtype mice. While the authors did not identify difference in the two mouse populations in this area, the ability to thoroughly examine both the unprocessed precursor peptides and mature peptide hormones meant that the authors could be confident in minimising the role of these specific hormones as significant causes of the body mass disparity in the two groups. While it is challenging to use negative results to support or refute a hypothesis, the use of peptidomics in this study is a good example of how a lack of findings, or positive results, in a detailed examination of one specific component of a pathways, e.g. hormone processing, can be used to advocate for future studies of other components of the pathway, e.g. receptor sensitivity, which may be more fruitful.
How was PEAKS used?
PEAKS was used for Peptide identification by searching against the mouse SwissProt database. The integration of de novo sequencing into the database search workflow means that users can examine confidence levels for each amino acid in a identified peptide that has been matched to a database peptide, thus increasing overall confidence in the identification results.
Cimino, I., Rimmington, D., Tung, Y.C.L. et al. Murine neuronatin deficiency is associated with a hypervariable food intake and bimodal obesity. Sci Rep 11, 17571 (2021). doi:10.1038/s41598-021-96278-8
Neuronatin (Nnat) has previously been reported to be part of a network of imprinted genes downstream of the chromatin regulator Trim28. Disruption of Trim28 or of members of this network, including neuronatin, results in an unusual phenotype of a bimodal body weight. To better characterise this variability, we examined the key contributors to energy balance in Nnat+/−p mice that carry a paternal null allele and do not express Nnat. Consistent with our previous studies, Nnat deficient mice on chow diet displayed a bimodal body weight phenotype with more than 30% of Nnat+/−p mice developing obesity. In response to both a 45% high fat diet and exposure to thermoneutrality (30 °C) Nnat deficient mice maintained the hypervariable body weight phenotype. Within a calorimetry system, food intake in Nnat+/−p mice was hypervariable, with some mice consuming more than twice the intake seen in wild type littermates. A hyperphagic response was also seen in Nnat+/−p mice in a second, non-home cage environment. An expected correlation between body weight and energy expenditure was seen, but corrections for the effects of positive energy balance and body weight greatly diminished the effect of neuronatin deficiency on energy expenditure. Male and female Nnat+/−p mice displayed subtle distinctions in the degree of variance body weight phenotype and food intake and further sexual dimorphism was reflected in different patterns of hypothalamic gene expression in Nnat+/−p mice. Loss of the imprinted gene Nnat is associated with a highly variable food intake, with the impact of this phenotype varying between genetically identical individuals.