De novo assembly of a transcriptome for the cricket Gryllus bimaculatus prothoracic ganglion: An invertebrate model for investigating adult central nervous system compensatory plasticity

Abstract

The auditory system of the cricket, Gryllus bimaculatus, demonstrates an unusual amount of anatomical plasticity in response to injury, even in adults. Unilateral removal of the ear causes deafferented auditory neurons in the prothoracic ganglion to sprout dendrites across the midline, a boundary they typically respect, and become synaptically connected to the auditory afferents of the contralateral ear. The molecular basis of this sprouting and novel synaptogenesis in the adult is not understood. We hypothesize that well-conserved developmental guidance cues may recapitulate their guidance functions in the adult in order to facilitate this compensatory growth. As a first step in testing this hypothesis, we have generated a de novo assembly of a prothoracic ganglion transcriptome derived from control and deafferented adult individuals. We have mined this transcriptome for orthologues of guidance molecules from four well-conserved signaling families: Slit, Netrin, Ephrin, and Semaphorin. Here we report that transcripts encoding putative orthologues of most of the candidate developmental ligands and receptors from these signaling families were present in the assembly, indicating expression in the adult G. bimaculatus prothoracic ganglion.

Characterization of plexinA and two distinct semaphorin1a transcripts in the developing and adult cricket Gryllus bimaculatus

“…This putative PlexA protein appeared to be fairly well‐conserved, sharing reasonably high levels of identity with PlexA in C. secundus (termite) and D. melanogaster . As previously characterized, G. bimaculatus PlexA shares the same domain type, number and order as compared to D. melanogaster PlexA (Fisher et al, ), indicating that this protein's structure, and presumably its functions, are well‐conserved.…”

“…A 5′ portion of sema1a was identified from a published transcriptome (Zeng et al, ), and was confirmed and extended by searching our recent de novo transcriptome assembly, which is based on adult control and deafferented prothoracic ganglia (Fisher et al, ). A second, distinct sema1a was identified in a draft genome for G. bimaculatus (Mito and Noji, personal communication), which we confirmed and extended with a search of our recently assembled transcriptome (Fisher et al, ). A majority of both sequences were amplified and confirmed from independent prothoracic ganglion and embryonic samples using PCR and Sanger sequencing.…”

“…We identified a plexA transcript predicted to encode a full‐length PlexA protein from our assembled transcriptome. Our initial characterization indicates that PlexA in G. bimaculatus has the same number, type, and order of protein domains as PlexA (isoform A) in D. melanogaster (Fisher et al, ). We amplified and confirmed a majority of the predicted sequence from independent prothoracic and embryonic samples using PCR and Sanger sequencing.…”

“…ISH experiments in D. melanogaster have shown that s ema1b is not expressed in the PNS or CNS of the developing embryo, but is instead present in early oocytes and at the embryonic midline during gastrulation (Khare, Fascetti, DaRocha, Chiquet‐Ehrismann, & Baumgartner, ). This distinction could explain the absence of sema1b in our transcriptome, which is derived from adult CNS tissue (Fisher et al, ). Moreover, a recent search of the GenBank database indicates that Sema1b may be limited to Diptera, indicating that this protein might be a result of a fairly recent gene duplication.…”

“…The percent identity among the predicted G. bimaculatus Sema proteins indicates that these two Sema1a‐type proteins share more identity with Sema1a candidates than with non‐Sema1a candidates. In addition, a specific search for sema1b in our transcriptome did not identify any candidate sequences (Fisher et al, ). There are many technical reasons that sema1b may not be represented in our transcriptome, but we have reason to suspect that it is truly absent.…”