Yolk proteins of the schistosomiasis vector snail Biomphalaria glabrata revealed by multi-omics analysis

Abstract

Vitellogenesis is the most important process in animal reproduction, in which yolk proteins play a vital role. Among multiple yolk protein precursors, vitellogenin (Vtg) is a well-known major yolk protein (MYP) in most oviparous animals. However, the nature of MYP in the freshwater gastropod snail Biomphalaria glabrata remains elusive. In the current study, we applied bioinformatics, tissue-specific transcriptomics, ovotestis-targeted proteomics, and phylogenetics to investigate the large lipid transfer protein (LLTP) superfamily and ferritin-like family in B. glabrata. Four members of LLTP superfamily (BgVtg1, BgVtg2, BgApo1, and BgApo2), one yolk ferritin (Bg yolk ferritin), and four soma ferritins (Bg ferritin 1, 2, 3, and 4) were identified in B. glabrata genome. The proteomic analysis demonstrated that, among the putative yolk proteins, BgVtg1 was the yolk protein appearing in the highest amount in the ovotestis, followed by Bg yolk ferritin. RNAseq profile showed that the leading synthesis sites of BgVtg1 and Bg yolk ferritin are in the ovotestis (presumably follicle cells) and digestive gland, respectively. Phylogenetic analysis indicated that BgVtg1 is well clustered with Vtgs of other vertebrates and invertebrates. We conclude that, vitellogenin (BgVtg1), not yolk ferritin (Bg yolk ferritin), is the major yolk protein precursor in the schistosomiasis vector snail B. glabrata.

Figure 1

(A) A schematic diagram showing the modular architecture of 4 LLTP proteins, BgVtg1, BgVtg2, BgApo1, and BgApo2 (not drawn to scale). RPT: Internal Repeats. (B) A heatmap showing the relative expression of 4 LLTP proteins, BgVtg1, BgVtg2, BgApo1, and BgApo2 in 11 tissues of B. glabrata.

Figure 2

(A) A mRNA sequence of Bg yolk ferritin. Nucleotides in purple color are coding sequences. (B) A comparison of the deduced amino acid (aa) sequences of yolk ferritin between B. glabrata and L. stagnalis. Sequence in pink color is single peptide (SP) and sequence in red is the 42-aa insert sequence. (C) A heatmap showing relative expression of the yolk ferritin and four cytoplasmic ferritins in 11 tissues of B. glabrata.

Figure 3

(A,B) show phylogenetic analysis of LLTP proteins and ferritin-like proteins, respectively. Bootstraps < 60% are not shown. The number in parenthesis is a GenBank accession number.