The AROM Gene, Spliced mRNAs Encoding New DNA/RNA-binding Proteins Are Transcribed from the Opposite Strand of the Melanin-concentrating Hormone Gene in Mammals

Abstract

Melanin-concentrating hormone (MCH)1 is a cyclic peptide, first isolated from salmon pituitary glands on the basis of its skin paling property (1), then purified from rat hypothalami, and sequenced (2). Synthesis of MCH was localized almost exclusively in a large population of neurons present in the zona incerta and lateral hypothalamus area of the mammalian brain (3-5). The MCH axonal network projected widely throughout the brain and posterior pituitary but innervated poorly the external part of the median eminence in resting animals (5). This particular cellular and axonal distribution argued in favor of a neurotransmitter/neuromodulator role for MCH in a large spectrum of functions in the central nervous system (reviewed in Refs. 6 and 7). Recently, several laboratories have demonstrated changes in different behaviors following intracerebroventricular injection of MCH in the rat brain. In particular, MCH plays a particularly important role in the regulation of feeding behavior and associated pathologies such as obesity (8 -11). Given the important biological functions of MCH, it is of great interest to define the mechanisms that regulate the expression of its cognate gene. A single MCH-encoding gene has been identified in both rat and mouse (12, 13), and two distinct MCH gene systems have been found in primates (14, 15). The regulation of MCH gene expression has been most extensively investigated with in vivo models (reviewed in Ref. 7). However, we established recently that production of mature MCH mRNA (0.95 kb in length) can be induced in PC12 cells following treatment with nerve growth factor (NGF) and lithium (16,17). Interestingly, we identified MCH RNA species of high molecular weight (1.4, 3.5, and 4.0 kb in length) in unstimulated PC12 cells; those transcripts transiently disappearing after a short term treatment with NGF and lithium. Because the increase in MCH mRNA content was not apparently associated with transcriptional activation, we hypothesized that some of the large MCH gene-related transcripts could be involved in the regulation of the processing or degradation of the MCH mRNA (16,17).In the present study, we described the isolation and characterization of the high molecular weight MCH RNAs in PC12 cells and in rat tissues. Interestingly, they are derived from a new gene located on the opposite DNA strand to the MCH gene, with extensive overlap existing between the 3Ј end of this gene and the MCH transcriptional unit. Some of the antisense MCH RNAs display alternative splicing and encode new DNA/RNAbinding proteins, whereas other putative transcripts lack extensive open reading frames suggesting different functions for the two classes of antisense MCH RNAs.

The four Rs of RNA-directed evolution

“…Silencing of genes may result when insertion produces new SATs. Alternative splicing may develop when reverse transcription of an antisense RNA copies into a gene those sense-strand sequences that encode introns 74 . Species-specific promoters may evolve through spread of RNA scaffolds by reverse transcription.…”

“…Unlike the creation of new protein domains by exon shuffling, this mode of evolution is not constrained by the need to maintain reading frame 74 . Nor is it constrained by the selective pressures that have conserved promoter and enhancer sequences over the millions of years that separate fish and humans 87 .…”

Melanin-concentrating hormone 1 receptor-deficient mice are lean, hyperactive, and hyperphagic and have altered metabolism

“…6), as well as encode a portion of the recently identified antisense-RNA-overlapping-MCH (AROM; ref. 7). Two recently described mouse genetic models further implicate MCH in the regulation of energy homeostasis.…”

Late-Onset Leanness in Mice with Targeted Ablation of Melanin Concentrating Hormone Neurons

“…The diverse functions of MCH are mediated by two G-protein-coupled receptors, MCH-R1 and MCH-R2 (Chambers et al, 1999;Hill et al, 2001). MCH neuropeptides are derived from a larger prohormone precursor, which also encodes other putative neuropeptides including EI, neuropeptide GE, MCH gene overprinted polypeptide, and antisense RNA overlapping MCH (Bittencourt et al, 1992;Toumaniantz et al, 1996;Borsu et al, 2000). The biological role of these additional neuropeptides is not fully established.…”