Characterization of a female-specific cDNA derived from a developmentally regulated mRNA in the human blood fluke Schistosoma mansoni.

Abstract

We have isolated and characterized a cDNA clone that is derived from a developmentally regulated mRNA found only in mature female schistosomes. The mRNA is approximately 950 nucleotides in length and is not detectable in immature female schistosomes isolated from single-sex infections, in male worms, or in eggs. During normal bisexual infections, the mRNA species is first detected 28 days after infection (the time of worm pairing) and increases to a high level 35 days after infection, coinciding with the start of egg production. The nucleotide sequence of the cDNA shows two large open reading frames in the coding strand. Several features of the clone, including the deduced sequence of the polypeptide encoded by one of the reading frames, suggest a relationship to the silk moth chorion (egg shell) gene family.The isolation of this clone provides us with a probe for further studies of female schistosome development and is a first step toward a detailed understanding of this process at the molecular level.Schistosomes are multicellular parasites whose life cycle includes both human and snail hosts. Schistosoma mansoni, as the other species that infect humans, inhabits the bloodstream of man. Infection begins when cercariae penetrate unbroken skin of humans who are in contact with fresh water containing Schistosoma. Once the skin is penetrated, the transformed parasite, termed a schistosomule, remains in the interstitial tissue for 2 days, then enters the circulation, and migrates to the lungs. By day 7-14 the parasites leave the lungs and migrate to the liver where male and female worms mate (approximately day 28), and encopula move to their final niche in the mesenteries. Egg laying commences about day 35 (1).Unlike most trematode parasites, schistosomes are dioecious. S. mansoni has 8 pairs of chromosomes, and the female schistosome is heterogametic (2). Sex is determined in the zygote, which develops into an embryonated egg.Earlier studies dealing with female maturation and development demonstrated that the presence of the male worm is necessary for full growth and complete sexual maturation of the female (3, 4). Female worms obtained from single-sex infections are stunted and not sexually developed (3, 5), although male worms from single-sex infections appear normal (6, 7). Moreover, Clough (8) showed that male worms are necessary to maintain, as well as to initiate, female maturation and fecundity. When sexually mature female worms are removed from their male partners, they stop laying eggs and regress to a condition morphologically resembling immature female parasites, until they are reunited with mature male worms. The stimulus from the male schistosome responsible for female growth, maturation, and fecundity is independent of sperm transfer (6, 7, 9), but its exact nature is unresolved (4, 10-12).The unusual interplay between male and female schistosomes in the regulation of female development provides a unique system to study sexual differentiation. Moreover, since the production of eggs by mature ...

Small gene family encoding an eggshell (chorion) protein of the human parasite Schistosoma mansoni.

“…There was a strong correlation between the amino acid composition of this protein and the actual composition of the schistosome eggshell (4). This fact, in addition to the biological context in which the mRNA was found, the significant homology in sequence to the silkmoth chorion gene family (3), and the recognition of an eggshell protein of 14 kDa by an antiserum directed against a peptide from the deduced amino acid sequence of the cDNA clone (unpublished data), led us to conclude that the clone encoded a protein that is a major component of the schistosome eggshell (chorion).…”

“…Our data indicated that there were approximately five copies per haploid genome. We also showed that these genes did not amplify or rearrange during schistosome development (1,3).…”

“…This mRNA appeared to be developmentally regulated, since it was not found in any other parasite stage. The accumulation of the mRNA in schistosome females coincided temporally with the pairing of females with male schistosomes and with subsequent egg production (1,3).…”

“…Like the chorion genes of the silkmoth and Drosophila melanogaster, the eggshell protein genes of S. mansoni are developmentally regulated, showing a high sex, tissue, and temporal specificity of expression (1,3,5,8,21). The silkmoth chorion (eggshell) consists of more than 100 different proteins, encoded by a large number of genes belonging to a gene superfamily with two symmetrical branches, each consisting of three families (7,12).…”

Cloning and Characterization of a Schistosoma mansoni cDNA Clone with a Specific Antigenic Expression during Development in a Vertebrate Host

“…This antigen named Sm44 has a specific antigenic expression since only serum related to the chronic phase is able to recognize it although in terms of RNA expression the Sm44 antigen of S. mansoni is also present in other evolutionary phases of parasitism but is excluded by the immune system perhaps by some block due to host molecule incorporation or different distribution during the development of the parasite in vertebrate hosts, similar to other antigens described previously (Aronstein & Strand 1983, Harn et al 1985, Davies et al 1986, Stein & David 1986, Bobek et al 1986, Grossman et al 1990, Menrath et al 1995.…”