Identification of genes related to learning and memory in the brain transcriptome of the mollusc,Hermissenda crassicornis

Abstract

The sea slug Hermissenda crassicornis (Mollusca, Gastropoda, Nudibranchia) has been studied extensively in associative learning paradigms. However, lack of genetic information previously hindered molecular-level investigations. Here, the Hermissenda brain transcriptome was sequenced and assembled de novo, producing 165,743 total transcripts. Orthologs of 95 genes implicated in learning were identified. These included genes for a serotonin receptor and a GABA-B receptor subunit that had not been previously described in molluscs, as well as an adenylyl cyclase gene not previously described in gastropods. This study illustrates the Hermissenda transcriptome's potential as an important genetic tool in future learning and memory research.[Supplemental material is available for this article.]Nervous systems of molluscs have been a focus of neuroscience research for many decades, yet their study has been impeded by lack of genetic information. The nudibranch Hermissenda crassicornis exhibits a simple form of associative learning, which has been studied extensively: it can learn to associate light changes with vestibular stimulation (Crow and Alkon 1978). The neural correlates of Hermissenda's associative memories formed during lightmovement pairings have been uncovered (Alkon 1980;Crow and Alkon 1980;Britton and Farley 1999;Tamse et al. 2003;Cavallo et al. 2014). Hermissenda has also been the subject of investigations related to many other aspects of neuroscience, including sensory and motor neuron physiology (Crow and Tian 2004;Nesse and Clark 2010;Jin and Crow 2011;Crow et al. 2013) and the evolution of behaviors and neurotransmitter systems Newcomb et al. 2012;Lillvis and Katz 2013). A limited number of molecular-level studies have been performed on Hermissenda in these areas (Nelson and Alkon 1988;Crow et al. 1997). Broader-scale genetic experiments, such as identification of genes or specific genetic isoforms that produce proteins involved in Hermissenda associative learning, have been impossible without more extensive genetic information specifically from Hermissenda.Transcriptomes have been sequenced in a small number of other gastropod species, including neuronal transcriptomes from Aplysia californica (Moroz et al. 2006;Fiedler et al. 2010;Heyland et al. 2011), A. kurodai (Lee et al. 2008Choi et al. 2010), Lymnaea stagnalis (Bouetard et al. 2012;Sadamoto et al. 2012), and Tritonia diomedea (Senatore et al. 2015), which have been used in studies of learning and other aspects of neuroscience. The field of molluscan neurogenomics is growing thanks in large part to recent advances in sequencing technologies, which allow larger amounts of transcriptomic information to be sequenced at lower costs compared with technologies available a few years ago.In this study, we describe the brain transcriptome of the sea slug Hermissenda crassicornis. The transcriptome was sequenced from central nervous system tissue mRNA, which included the cerebropleural ganglia, pedal ganglia, optic ganglia, eyes, and statocyst hair cells. S...

Sequences of Circadian Clock Proteins in the Nudibranch Molluscs Hermissenda crassicornis, Melibe leonina, and Tritonia diomedea

“…Sequencing and TSA metrics were previously provided for Hermissenda (Tamvacakis et al, 2015) and Tritonia (Senatore et al, 2015). For Melibe , sequencing resulted in 123,087,512 paired-end reads, 94.5% of which had a Phred score greater than 30.…”

“…Previously published CNS transcriptomes were used for Hermissenda and Tritonia (Senatore et al, 2015; Tamvacakis et al, 2015), while the Melibe transcriptome was developed using 15 specimens collected by Monterey Abalone Company (Monterey, CA). Total RNA was extracted from the CNS (the fused cerebropleural and pedal ganglia, plus the buccal ganglia), using an RNeasy Plus Universal Midi Kit (QIAGEN, Hilden, Germany).…”

“…, default parameters). A de novo transcriptome shotgun assembly (TSA) was then developed using Trinity (release 2013-08-14; Grabherr et al, 2011; Haas et al, 2013; Senatore et al, 2015; Tamvacakis et al, 2015). …”

“…The goal of this study was to identify the core circadian gene products in the central nervous systems (CNS) of three nudibranchs that are common neurophysiological model systems: Hermissenda crassicornis (Eschscholtz, 1831), Melibe leonina (Gould, 1852), and Tritonia diomedea Bergh, 1894 (synonym = Tritonia tetraquetra [Pallas, 1788]), using bioinformatic analyses of recently assembled transcriptomes (Senatore et al, 2015; Tamvacakis et al, 2015). Gene products were identified in all three species for a number of canonical clock genes, as well as some associated sequences, and compared to sequences in clock proteins in other species.…”

Investigating the Potential Signaling Pathways That Regulate Activation of the Novel PKC Downstream of Serotonin in Aplysia

“…One possibility is that there is an additional 5HT2 receptor in Aplysia . In their recent publication of the Hermissenda transcriptome, Katz and colleagues identified a 5HT2 receptor with more similarity to arthropod 5HT 2B receptors than to the 5HT 2Apl receptor we had cloned [46]. The NCBI database reveals a receptor that may be the orthologue of this Hermissenda receptor (XP_012935429.1) in Aplysia .…”