Two neuron clusters in the stem of postembryonic zebrafish brain specifically express relaxin‐3 gene: First evidence of nucleus incertus in fish

Abstract

We examined the spatial expression of the relaxin-3 gene in the developing zebrafish brain, one of the vertebrate model systems in which this gene has been identified. Until the pharyngula stage, the gene is expressed diffusely in the brain, where, starting at about 40 hpf, the transcripts appear restricted in a midbrain cell cluster of the periaqueductal gray. Later, at 72 hpf, the transcripts are still evident in that cluster and distributed in a larger cell number; at this stage, the gene is also expressed posteriorly, in a smaller cell group that, as we report for the first time, could be homologous to mammalian nucleus incertus.

Increased feeding and body weight gain in rats after acute and chronic activation of RXFP3 by relaxin-3 and receptor-selective peptides

“…Phylogenetic studies have shown that the peptide and its sites of expression have been highly conserved from zebrafish to the macaque (Donizetti et al, 2008;Ma et al, 2009b). Unlike other RXFPs, relaxin-3 is predominantly expressed in the brain, by neurons in several areas of the brainstem, including the nucleus incertus, pontine raphé nucleus and ventrolateral periaqueductal grey Tanaka et al, 2005;Ma et al, 2007).…”

Relaxin-3 systems in the brain—The first 10 years

“…In other anatomical studies, relaxin-3 mRNA expression was observed in zebrafish in a cluster of cells in the midbrain periaqueductal grey, and in a more posterior cell group, which is a likely equivalent of the rodent nucleus incertus (Donizetti et al, 2008;Donizetti et al, 2009). Although a primate equivalent of the rodent nucleus incertus is yet to be formally characterised, recent studies in the macaque (Macaca fascicularis) detected relaxin-3 mRNA and relaxin-3 IR in large, elongated neurons within the ventromedial central grey at the level of the tegmentum, while sparse relaxin-3 positive cells were also detected in the periaqueductal grey (Ma et al, 2009b), representing populations of relaxin-3 neurons homologous to those detected in the equivalent regions in the rodent Smith et al, 2010).…”

“…Although limited peripheral expression of relaxin-3 has been reported (Liu et al, 2003b), the main site of relaxin-3 mRNA expression is the brain, where it has been detected in high concentrations in species including the zebrafish (Donizetti et al, 2008), mouse (Bathgate et al, 2002a;Smith et al, 2010), rat Tanaka et al, 2005), macaque (Ma et al, 2009b), and human (Liu et al, 2003b). Expression in brain is neuronal in nature and ultrastructural examinations of rat brain Relaxin-3 expressing neurons in the nucleus incertus of mouse brain.…”

Relaxin family peptide systems and the central nervous system

“…Recently, a study of relaxin-3 expression in zebrafish highlighted the similarities in expression between rodents and the non-mammalian vertebrate [83]. In post-embryonic zebrafish, relaxin-3 expression is restricted to two groups of neurons, the first near the fourth ventricle, which also express type 1 corticotrophin releasing factor receptor (CRF-R1) and the second in the PAG, as confirmed by colocalization with proenkephalin-like gene 1.…”