Sequencing and expression analysis of a Schistosoma mansoni gene homologue to a Drosophila gene involved in germ plasm assembly

Schistosoma mansoni; mago nashi; germ plasm; gene characterization; sequencing

RESEARCH NOTE

Sequencing and Expression Analysis of a Schistosoma mansoni Gene Homologue to a Drosophila Gene Involved in Germ Plasm Assembly

Vol. 93, Suppl. I: 207-209

Élida ML Rabelo/⁺, Adriano BS Hobaika, Paulo Marcos Z Coelho, Sérgio DJ Pena*

Departamento de Parasitologia *Departamento de Bioquímica e Imunologia, ICB, Universidade Federal de Minas Gerais, Av. Antônio Carlos 6627, 31270-901 Belo Horizonte, MG, Brasil

Key words: Schistosoma mansoni - mago nashi - germ plasm - gene characterization - sequencing

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Genes coding for proteins involved in gene regulation and/or development are of great interest in the study of the biology of Schistosoma mansoni. This trematode is the etiologic agent of schistosomiasis and presents a complex life cycle with drastic morphologic changes between stages. Recently, some strains have become resistant to the drugs currently in use to eradicate the disease (D Cioli et al. 1995 Pharmac Ther 68: 35-85). The strategy of gene discovery program in S. mansoni by using the EST (expressed sequence tag) approach (GR Franco et al. 1995 Gene 152: 141-147) has been very efficient in the discovery of new S. mansoni genes, which were unlikely to be identified using classical procedures based on phenotype. A class of genes that interested us particularly were those that in other organisms were known to be involved in the regulation of embryogenesis. Among these, we selected one that presented a high homology to a Drosophila gene named mago nashi. In diptera this gene is involved in the process of germ plasm assembly and its mutation results in sterility of F1 progeny and also in the formation of the perpendicular axes (RE Boswell et al. 1991 Development 113: 373-384). We reasoned that this gene might conceivably play a role in the morphogenetic changes seen in the life cycle of the parasite. We thus decided to characterize S. mansoni mago nashi further by obtaining its full length cDNA and genomic sequences, as well as studying its expression pattern at the different life stages of the worm.

The whole cDNA was sequenced in both directions yielding 485 nucleotides (nt) that coded for a protein of 146 amino acids with 84% of homology to the Drosophila homologue (Fig. 1). Procedures for plasmidial DNA preparation, sequencing and analysis of sequences have been previously described (Franco loc. cit.). From the cDNA sequence, primers were designed and the genomic gene amplified from S. mansoni total DNA. The genomic amplified product was bigger than the correspondent cDNA amplified product when two different pairs of primers were used (Fig. 2). The PCR amplification products were cloned in a plasmid vector (pUC18) by using the Pharmacia Sure clone kit and sequenced in both directions using fluorescent primers in an automated DNA sequencer. Consistent with the results of Fig. 2, three introns were identified in the genomic sequence, two of 34 nt and one with 33 nt producing a total of a 101 nt of intron sequences (Fig. 3).

Our next step was to investigate the gene expression pattern at the different life cycle stages. Through the RT-PCR technique using cDNA obtained from different stages and specific primers, it was shown that mago nashi is expressed in all stages studied i.e. egg, schistosomula and adult worm (data not shown). This was not unexpected although this gene was first identified in drosophila embryos, it was also identified in adult flies (PA Newmark & RE Boswell 1994 Development 120: 1303-1313). The gene had also been shown to be expressed in a large variety of human adult tissues such as lung, kidney, liver, heart, pancreas, brain and placenta (X- Zhao et al. 1998 Genomics 47: 319-322).

Since this work was started, the mago nashi gene has been identified in a variety of different organisms. These include mouse, human, Caenorhabditis elegans, Brugia malayi, Arabidopsis thaliana and Oryza sativa. Alignment of the conceptual translations of these mago genes reveals that 63% of the residues are identical in all homologues identified and many of the remaining positions show only conservative substitutions (DR Micklem et al. 1977 Current Biology 7: 468-478).

Although a specific function has not been assigned to mago nashi, the fact that the protein seems highly conserved during evolution between animals and plants and is not detected in yeast or bacteria, suggests that it plays some fundamental role in multicellular eukaryotes. The expression of the protein and antibody production will permit the protein immunolocalization shedding some light about the possible functional role it is playing in S. mansoni.

: to Dr José Miguel Ortega for helping with the sequence alignments.

Fig. 1 | Fig. 2 | Fig. 3

This investigation received financial support from UNDP/WORLD BANK/WHO Special Programme for Research in Tropical Diseases (ID no. 940325, 940751); Fapemig Process No. CBS 2205/96; CNPq and PADCT.

Sequence data from this article have been deposited in dBEST and GenBank under accession no. AAA125719

⁺Corresponding author. Fax: [phone].

Received 4 May 1998

Accepted 31 August 1998

Figure 1

Figure 2

Figure 3

Publication Dates

• Publication in this collection
  14 July 2000
• Date of issue
  1998

History

• Accepted
  31 Aug 1998
• Received
  04 May 1998