Isolation and Characterization of Five Actin cDNAs from the Cestode Diphyllobothrium dendriticum: A Phylogenetic Study of the Multigene Family

Abstract

Five cDNAs (pDidact2-pDidact6), representing different actin genes, were isolated from a Diphyllobothrium dendriticum cDNA library, and the DNA as well as the putative amino acid sequences were determined. The corresponding Didact2 and Didact4 genes code for peptides 376 amino acids long, with molecular weights 41,772 and 41,744 Da, respectively, while the deduced Didact3 protein is 377 amino acids long and weighs 41,912 Da. The pDidact5 and -6 cDNAs lack nucleotides corresponding to three to six amino acids at the amino-terminus. Two of the five cDNAs contain the conventional AATAAA as the putative polyadenylation signal, one has the common variant ATTAAA, whereas the hexanucleotide AATAGA is found 15 and 18 nucleotides, respectively, upstream of the poly(A) site in two of the cDNAs. Phylogenetic studies including 102 actin protein sequences revealed that there are at least four different types of cestode actins. In this study three of these types were found to be expressed in the adult D. dendriticum tapeworm. Structurally the cestode actin groupings differ from each other to an extent seen only among the metazoan actins between the vertebrate muscle and cytoplasmic isoforms. In the phylogenetic trees constructed, cestode actins were seen to map to two different regions, one on the border of the metazoan actins and the other within this group. It is, however, difficult to say whether the cestode actins branched off early in the metazoan evolution or if this position in the phylogenetic tree only reflects upon differences in evolutionary rate.

Patterns of Variant Polyadenylation Signal Usage in Human Genes

“…The agreement between our results and the literature is excellent: those naturally occurring polyadenylation signals that do not figure in our list are either weakly active, deleterious, or found only in plants. Interestingly, the AAUAGA motif was reported as functional solely in flatworms (Wahlberg and Johnson 1997), while its presence in human ␤-globin mRNA in replacement of the canonical signal is a known cause of ␤-thalassemia (Jankovic et al 1990;van Solinge et al 1996). Mutations in poly(A) signals causing ␣-and ␤-thalassemia result in elongated mRNAs (Orkin et al 1985;Smetanina et al 1996), meaning the poly(A) signal either is not functional or is used inefficiently.…”

“…AAUACA Functional in 5 mammalian mRNAs (Suzuki et al 1990;Taylor et al 1990;Herve et al 1991;Myohanen et al 1991;Parthasarathy et al 1997), and 1 insect mRNA (Tokishita et al 1997). AAUAGA Functional in 1 Platyhelminthe (flatworm) mRNA (Wahlberg and Johnson 1997); deleterious in human ␤-globin mRNA (Jankovic et al 1990;van Solinge et al 1996). ACUAAA Functional in 1 mammalian mRNA (Trowsdale and Kelly 1985).…”

Actin expression in Taenia solium cysticerci (cestoda): tisular distribution and detection of isoforms

“…The latter expresses seven actin isoforms, as shown by two-dimensional gel electrophoresis (Abbas and Cain, 1989). Their presence in these helminths could correlate with different patterns of actin distribution found in other cestodes Stitt et al, 1992;Wahlberg and Johnson, 1997;Wahlberg, 1998). This differential expression appears to depend on the developmental stage (Abbas and Cain, 1989;Mair et al, 1998;Wahlberg, 1997Wahlberg, , 1998, and could be explained by the occurrence of a multiple actin gene family (Sheterline et al, 1998).…”

“…Two actin genes have been identified and sequenced in T. solium (Campos et al, 1990), but their tissue expression has not been studied. These genes have a high degree of homology with those of the cestode Diphyllobotrium dendriticum (Wahlberg et al, 1994;Wahlberg and Johnson, 1997) and the trematode Schistosoma mansoni (Oliveira and Kemp, 1995). In D. dendriticum, using in situ hybridization assays, three sets of actin expression patterns have been found (Wahlberg, 1997).…”

“…In D. dendriticum, using in situ hybridization assays, three sets of actin expression patterns have been found (Wahlberg, 1997). Two of these genes show high DNA homology with T. solium actin genes (Wahlberg and Johnson, 1997;Wahlberg, 1997). T. solium and S. mansoni DNA also show similar homologies to actin genes (Oliveira and Kemp, 1995).…”