Insights into the Evolution of Shells and Love Darts of Land Snails Revealed from Their Matrix Proteins

Abstract

Over the past decade, many skeletal matrix proteins that are possibly related to calcification have been reported in various calcifying animals. Molluscs are among the most diverse calcifying animals and some gastropods have adapted to terrestrial ecological niches. Although many shell matrix proteins (SMPs) have already been reported in molluscs, most reports have focused on marine molluscs, and the SMPs of terrestrial snails remain unclear. In addition, some terrestrial stylommatophoran snails have evolved an additional unique calcified character, called a “love dart,” used for mating behavior. We identified 54 SMPs in the terrestrial snail Euhadra quaesita, and found that they contain specific domains that are widely conserved in molluscan SMPs. However, our results also suggest that some of them possibly have evolved independently by domain shuffling, domain recruitment, or gene co-option. We then identified four dart matrix proteins, and found that two of them are the same proteins as those identified as SMPs. Our results suggest that some dart matrix proteins possibly have evolved by independent gene co-option from SMPs during dart evolution events. These results provide a new perspective on the evolution of SMPs and “love darts” in land snails.

Hydrophilic Shell Matrix Proteins ofNautilus pompiliusand The Identification of a Core Set of Conchiferan Domains

“…However, the number of the obtained proteins is reasonable, when compared with other previous studies (e.g. Euhadra quaesita = 55, Shimizu et al, 2019; Pinctada margaritifera = 45, Marie et al, 2012; Pinctada fucata = 75, Liu et al, 2015; Cepaea nemoralis = 59, Mann and Jackson, 2014). One of the possible advantages of using a shallow system for transcriptome sequencing is that, most of the sequences we obtained here were probably the most abundantly expressed transcripts, and thus, major SMPs, and not background expression genes accidentally picked-up.…”

“…Because of the stringency of our searches, and considering our highly fragmented transcriptome sequence data, there is a possibility that we did not pick up possibly conserved protein-coding gene sequences in our data. Therefore, we also conducted reciprocal local BLASTn searches using less stringent settings following previous studies (only by setting the maximum e-value of ≤e -5 ; Shimizu et al, 2019; Zhao et al, 2018) (“Search Setting 2”).…”

“…Among extant metazoans, two phyla have anciently evolved and are still retaining their external biomineralized shells: the mollusks (Mollusca) and the brachiopods (Brachiopoda) (Cowen, 2009). Most members of these calcifying organisms live in the marine environment, where calcium and carbonate ions are easily available as sources of the mineralized tissues (Shimizu et al, 2019).…”

Pearl Sac Gene Expression Profiles Associated With Pearl Attributes in the Silver-Lip Pearl Oyster, Pinctada maxima

“…Differentially expressed transcripts were further investigated to determine whether they (i) were likely to encode SMPs based upon similarity to proteins that had previously been identified from molluscan shells, (ii) possibly had regulatory roles (specifically, whether they were likely to have transcription regulatory or signaling activity), or (iii) whether they had similarity to transcripts that had been associated with pearl quality in a previous study ( Le Luyer et al, 2019 ). Similarity to SMPs was ascertained by performing BLASTP searches against an in-house database of published proteins that had previously been identified from the shells of other mollusc species ( Marie et al, 2010 , 2011 , 2012 , 2013b , 2017 ; Bédouet et al, 2012 ; Mann et al, 2012 , 2018 ; Pavat et al, 2012 ; Zhang et al, 2012 ; Mann and Jackson, 2014 ; Gao et al, 2015 ; Liao et al, 2015 , 2019 ; Liu et al, 2015 ; Arivalagan et al, 2016 ; Upadhyay et al, 2016 ; Le Pabic et al, 2017 ; Shimizu et al, 2018 ), using an e-value cut-off of 1e –10 . Reciprocal BLAST searches were then performed against the parent taxon of the top BLAST hit in NCBI to provide evidence for transcript homology.…”

Data_Sheet_1.PDF

“…Differentially expressed transcripts were further investigated to determine whether they (i) were likely to encode SMPs based upon similarity to proteins that had previously been identified from molluscan shells, (ii) possibly had regulatory roles (specifically, whether they were likely to have transcription regulatory or signaling activity), or (iii) whether they had similarity to transcripts that had been associated with pearl quality in a previous study (Le Luyer et al, 2019). Similarity to SMPs was ascertained by performing BLASTP searches against an in-house database of published proteins that had previously been identified from the shells of other mollusc species (Marie et al, 2010(Marie et al, , 2011(Marie et al, , 2012(Marie et al, , 2013b(Marie et al, , 2017Bédouet et al, 2012;Mann et al, 2012Mann et al, , 2018Pavat et al, 2012;Zhang et al, 2012;Mann and Jackson, 2014;Gao et al, 2015;Liao et al, 2015Liao et al, , 2019Liu et al, 2015;Arivalagan et al, 2016;Upadhyay et al, 2016;Le Pabic et al, 2017;Shimizu et al, 2018), using an e-value cut-off of 1e −10 . Reciprocal BLAST searches were then performed against the parent taxon of the top BLAST hit in NCBI to provide evidence for transcript homology.…”