In vitro culture media type impacts gene expression in the freshwater mussel Lampsilis siliquoidea (Bivalvia: Unionidae)

Abstract

Artificial propagation is an important conservation technique to mitigate the loss of native freshwater mussel diversity. In vitro propagation is an alternative method of metamorphosing freshwater mussel larvae (glochidia) to juveniles without a host fish, but the methodology is still evolving in its rates of metamorphosis. This study provides the first comparison of gene expression in freshwater mussel glochidia metamorphosed in different culture media: M199, L-15, and M199 supplemented with lipids. Compared to the commonly used M199, 1.2% of the transcriptome of glochidia reared in the other culture media showed significantly altered expression levels. Of these differentially expressed transcripts, 86% were the same regardless of whether glochidia were metamorphosed in the different basal culture medium L-15 or in M199 supplemented with lipids. We discuss the Gene Ontology categories with the highest number of differentially expressed transcripts, as well as those categories that were over-represented in the different culture media compared to the whole transcriptome. Our results suggest that the external environment can have a significant impact on the physiology of metamorphosing glochidia and may potentially impact the health and survival of juveniles.

Keywords: Freshwater mussels; Gene expression; Glochidia; In vitro propagation; Transcriptomics; Unionidae.

Fig. 1

Number of transcripts assigned to Gene Ontology terms from the “biological process” (a), “molecular function” (b), and “cellular component” (c) domains

Fig. 2

Overrepresented GO terms for (a) downregulated and (b) upregulated transcripts from glochidia transformed in L-15 medium (L15) compared to M199 medium. Top (blue) bars represent the entire transcriptome. Bottom (red) bars represent the differentially expressed subset

Fig. 3

Overrepresented GO terms for (a) downregulated and (b) upregulated transcripts from glochidia transformed in M199 medium supplemented with lipids (M199 + lipids) compared to M199 medium. Top (blue) bars represent the entire transcriptome. Bottom (red) bars represent the differentially expressed subset. ¹Oxidoreductase activity, acting on paired donors, with incorporation or reduction of molecular oxygen. ²Oxidoreductase activity, acting on paired donors, with incorporation or reduction of molecular oxygen, reduced ascorbate as one donor, and incorporation of one atom of oxygen. ³Dopamine beta-monooxygenase activity