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Possible eggshell protein gene from Schistosoma mansoni
Abstract:
We have identified and sequenced a cDNA clone of a mRNA found only in mature female schistosomes. This mRNA is not detectably synthesized by female worms from single sex infections (unisexual females), by males or by the developing miracidia in the eggs. The clone hybridises to a highly abundant polyadenylated mRNA of approximately 1500 nucleotides. The nucleotide sequence of the clone predicts a polypeptide comprising two repetitive regions. A pentapeptide repeat with the consensus sequence Gly-Tyr-Asp-Lys-Tyr, and a region rich in histidine residues. Hybrid selected mRNA translated in vitro with [3H]tyrosine as labelled amino acid yields a polypeptide of 48 kDa (p48) that corresponds to the major [3H]tyrosine labelled translation product of female worm total mRNA. p48 does not label with [35S]methionine and is absent from the translation products of male and unisexual female mRNAs. The amino acid sequence of p48 has significant homologies to silk moth chorion proteins and we suggest that it is one of the major components of the schistosome eggshell probably accounting for the high level of [3H]tyrosine incorporation into the vitellaria of Schistosoma mansoni. The tyrosine content of the polypeptide suggests that it may play a role in phenol oxidase mediated cross-linking of the schistosome eggshell and in support of this we find that mushroom phenol oxidase will cause the specific cross-linking of p48 in in vitro translation products.
Insights
Researchers identified a unique mRNA in female schistosomes, crucial for eggshell formation. This mRNA codes for a protein rich in tyrosine and histidine, essential for eggshell cross-linking and structural integrity.
Area of Science:
- Parasitology
- Molecular Biology
- Biochemistry
Background:
- Schistosomes are parasitic flatworms causing significant human disease.
- The complex lifecycle of schistosomes involves distinct male and female adult stages.
- Eggshell formation is critical for schistosome survival and transmission.
Purpose of the Study:
- To identify and characterize novel genes expressed specifically in mature female schistosomes.
- To elucidate the function of a highly abundant mRNA found exclusively in female worms.
- To investigate the role of a specific protein in schistosome eggshell structure and cross-linking.
Main Methods:
- cDNA cloning and sequencing of a female-specific mRNA.
- Hybridization analysis to assess mRNA abundance and distribution.
- In vitro translation of hybrid-selected mRNA and protein characterization (e.g., radiolabeling).
- Bioinformatic analysis for sequence homology and functional prediction.
Main Results:
- Identified and sequenced a female-specific mRNA encoding a 48 kDa polypeptide (p48).
- p48 contains repetitive regions, including a pentapeptide repeat (Gly-Tyr-Asp-Lys-Tyr) and histidine-rich segments.
- p48 is the major tyrosine-labeled translation product in female worms and is absent in males and unisexual females.
- p48 shows homology to silk moth chorion proteins and is cross-linked by phenol oxidase in vitro.
Conclusions:
- The identified mRNA and its protein product (p48) are key components of the schistosome eggshell.
- The high tyrosine content of p48 suggests its involvement in phenol oxidase-mediated eggshell cross-linking.
- This protein likely plays a vital role in the structural integrity and development of schistosome eggs.