Differential distribution and energy status–dependent regulation of the four CART neuropeptide genes in the zebrafish brain

Abstract

The cocaine- and amphetamine-regulated transcript (CART) neuropeptide has been implicated in the neural regulation of energy homeostasis across vertebrate phyla. By using gene-specific in situ hybridization, we have mapped the distribution of the four CART mRNAs in the central nervous system of the adult zebrafish. The widespread neuronal expression pattern for CART 2 and 4 suggests a prominent role for the peptide in processing sensory information from diverse modalities including olfactory and visual inputs. In contrast, CART 1 and 3 have a much more restricted distribution, predominantly located in the nucleus of the medial longitudinal fasciculus (NMLF) and entopeduncular nucleus (EN), respectively. Enrichment of CART 2 and 4 in the preoptic and tuberal areas emphasizes the importance of CART in neuroendocrine functions. Starvation resulted in a significant decrease in CART-positive cells in the nucleus recessus lateralis (NRL) and nucleus lateralis tuberis (NLT) hypothalamic regions, suggesting a function in energy homeostasis for these neurons. Similarly, the EN emerges as a novel energy status-responsive region. Not only is there abundant and overlapping expression of CART 2, 3, and 4 in the EN, but also starvation induced a decrease in CART-expressing neurons in this region. The cellular resolution mapping of CART mRNA and the response of CART-expressing nuclei to starvation underscores the importance of CART neuropeptide in energy processing. Additionally, the regional and gene-specific responses to energy levels suggest a complex, interactive network whereby the four CART gene products may have nonredundant functions in energy homeostasis.

Identification of prohormones and pituitary neuropeptides in the African cichlid, Astatotilapia burtoni

“…Multiple sequence alignment suggests greater sequence similarity between two pairs of CARTPT prohomones: CARTPT1 with CARTPT2 , and CARTPT3 with CARTPT4. O. latipes also has 6 CARTPT copies [71] and D. rerio has 4 CARTPT copies [72]. …”

The Neuroendocrine Regulation of Food Intake in Fish: A Review of Current Knowledge

“…Two CART isoforms have been identified in goldfish (Volkoff and Peter, 2001a) and common carp (Wan et al, 2012), and 4 in zebrafish (Akash et al, 2014) whereas, to date, only one form has been isolated for grass carp (Zhou et al, 2013; Liu et al, 2014), Characiformes [pirapitinga (serrasalmidae) (Volkoff, 2015a), pacu (serrasasalmidae) (Volkoff et al, 2017) and dourado (characidae) (Volkoff et al, 2016), red bellied piranha (serrasalmidae) (Volkoff, 2014a)], Salmoniformes [Atlantic salmon (Murashita et al, 2009a), rainbow trout (Figueiredo-Silva et al, 2012), Arctic charr (Striberny et al, 2015) and lake trout ( Salvelinus namaycush ) (Volkoff et al, 2007)], Siluriformes (channel catfish Kobayashi et al, 2008), Gadiformes (Atlantic cod Kehoe and Volkoff, 2007), Perciformes (cunner Babichuk and Volkoff, 2013), winter flounder (MacDonald and Volkoff, 2009a) and Atlantic halibut ( Hippoglossus hippoglossus ) (Gomes et al, 2015) (Pleuronectiformes), venomous toadfish Thalassophryne nattereri (Batrachoidiforme) (Magalhaes et al, 2006), rainbow smelt ( Osmerus mordax ) (Osmeriforme), pufferfishes ( Takifugu rubripes and Tetraodon nigroviridis , Tetraodontiforme) and stickleback Gasterosteus aculeatus (Gasterosteiforme) (cited in Murashita et al, 2009a). However, six forms of CART have been identified in the medaka (Beloniforme) (Murashita and Kurokawa, 2011) and seven forms in Senegalese sole Solea senegalensis (Pleuronectiforme), the highest number of CART genes reported to date in a vertebrate species (Bonacic et al, 2015).…”

Hypothalamic Integration of Metabolic, Endocrine, and Circadian Signals in Fish: Involvement in the Control of Food Intake

“…Subsequent experiments revealed that CART neurons are anatomical targets for systemic leptin to induce anorexia (Kristensen et al, 1998). In fish, CART mRNA was characterized in several species (Subhedar et al, 2014) but immunohistochemical localization of the CART peptide in brain was only studied in catfish by using antibodies against rat CART (Singru et al, 2007) or by in situ hybridization in zebrafish (Nishio et al, 2012; Akash et al, 2014). CART mRNA abundance decreased with food deprivation in cod (Kehoe and Volkoff, 2007), goldfish (Volkoff and Peter, 2001a), and Atlantic salmon (Murashita et al, 2009), and increased with re-feeding in channel catfish (Kobayashi et al, 2008) whereas post-prandial changes occurred in channel catfish (Peterson et al, 2012), goldfish (Volkoff and Peter, 2001a), and dourado (Volkoff et al, 2016).…”

“…As many other genes, CART is duplicated in the teleost genome and four different genes (CART1-4 or CART1, 2a, 2b, 4) encoding CART peptides are reported in zebrafish (Nishio et al, 2012) or up to seven genes in Senegalese sole (Bonacic et al, 2015). All of them are expressed in zebrafish CNS but only CART2 and 4 are produced in the hypothalamus (Akash et al, 2014). Unfortunately, CART/POMC colocalization in the neurons of the tuberal hypothalamus has not been assessed in fish yet.…”