Eggshell protein genes of Schistosoma mansoni that encode a 14 kDa protein have been shown to be highly conserved and expressed in a sex-, tissue-, and temporal-specific manner. To initiate studies on the eggshell protein genes of S. haematobium, a cDNA probe, pSMf 61-46, representing a S. mansoni eggshell protein mRNA was used to screen a S. haematobium genomic library. Of the seven independent recombinant clones isolated, two (λSH 2-1 and λSH 6-1) were analyzed and compared to those of S. mansoni. λSH 2-1 and λSH 6-1 each contain a different genomic copy of the gene encoding a 19.8 and 17.6 kDa protein, respectively. This is due to an additional 78 bp present in the coding region of λSH 2-1 relative to λSH 6-1. The rest of the coding sequences are identical, and the 5′ and 3′ untranslated regions are nearly identical. The deduced amino acid sequences of S. haematobium eggshell proteins are very rich in glycine (47 and 50%) when compared to 43.5% glycine in the protein encoded by S. mansoni. Long stretches of glycines, as many as 15 in a row, occur in the S. haematobium sequence. DNA comparison of the eggshell protein genes of the two schistosome species yielded an overall homology of 83.1%. The homology is much higher in the 5′ and 3′ untranslated regions than in the protein-coding regions. Genomic clones of both species contained second open reading frames, which appeared to be kept open as a consequence of the amino acid composition of the other. There are no introns in S. haematobium or S. mansoni eggshell protein genes, and the genomic Southern data indicated a similar arrangement of these genes in the genome of both species. Primer extension experiments and dideoxynucleotide sequencing of the RNA determined the mRNA cap site sequence as ATCAT and ATCAC in λSH 2-1 and λSH 6-1, respectively. Northern blot analysis determined the size of the mRNA to be about 1.0 kp. Expression of the RNA from these genes appears to be regulated in a manner similar to the corresponding genes in S. mansoni. mRNA is found only in mature females and first appears at 70 days after infection of hamsters. DNA sequence comparisons of the 5′ flanking regions of S. haematobium and S. mansoni eggshell protein genes to each other and to those of silkmoth and Drosophila revealed several short sequence elements that are shared. Particularly interesting is a hexanucleotide, TCACGT, found to be an essential cis-acting regulatory element for chorion gene expression of both silkmoth and Drosophila and now found in all S. haematobium and S. mansoni eggshell protein genes sequenced to date.
- Chorion genes
- DNA and protein sequence comparisons
- Developmental regulation of expression
- Eggshell protein genes
- cis-acting regulatory elements
ASJC Scopus subject areas
- Infectious Diseases