Bioinformatic analysis of the expression pattern of an intron-retaining isoform of the Agrp transcript in arcuate nucleus neurons of mice

Abstract

Known to be the regulatory center of hunger and satiety, the arcuate nucleus (ARC) harbors two neuronal populations that exert opposite effects on the regulation of food intake. Namely, AgRP and POMC neurons respectively trigger hunger and satiety. Although both neuronal groups are born within the same time interval in the developing hypothalamus of mouse, their peptidergic identities are established at distinct developmental timepoints. While the POMC identity is established as early as the embryonic period, the complete maturation of the AgRP peptidergic identity extends to the postnatal period. Previously, through RT-PCR, our group detected the presence of an Agrp transcript isoform that retained introns 3 and 4 (Agrp-i3,4) in the early postnatal, but not in the adult mouse hypothalamus. In this thesis project, the expression pattern of Agrp-i3,4 is analyzed in public RNA-seq datasets from ARC neurons of mice at different postnatal developmental stages. To identify intron retention events, iREAD was used, and to quantify the proportion of Agrp transcripts that retained introns 3 and 4, ASpli was employed. Using this bioinformatics approach, the largest proportion of Agrp-i3,4 was detected in ARC samples of P12 mice and there was a trend towards decreased retention of Agrp introns 3 and 4 at later developmental stages. Agrp-i3,4 was detected in poly-A RNA extracted from whole AgRP neurons, but not in the ribosomal fraction. On the other hand, food deprivation appeared to exert distinct effects on the proportion of the Agrp-i3,4 transcript depending on the duration of the fast. While in weaned mice fasted for 16 hours Agrp-i3,4 showed a slight increase, in adult mice fasted for 38 hours Agrp-i3,4 appeared to decrease. Unlike fasting, leptin treatment did not exert any effect on the retention of Agrp introns 3 and 4. Of note, IR was found in Agrp but not in other genes that characterize the ARC, such as Npy or Pomc. Taken together, the results presented in this thesis suggest that increased IR of the Agrp transcript may correlate with a lower maturation degree of the ARC during a time interval in which the AgRP peptidergic identity has not yet been fully established.