Translational machinery of the chaetognath Spadella cephaloptera: a transcriptomic approach to the analysis of cytosolic ribosomal protein genes and their expression.
BACKGROUND
Chaetognaths, or arrow worms, are small marine, bilaterally symmetrical metazoans. The objective of this study was to analyse ribosomal protein (RP) coding sequences from a published collection of expressed sequence tags (ESTs) from a chaetognath (Spadella cephaloptera) and to use them in phylogenetic studies.


RESULTS
This analysis has allowed us to determine the complete primary structures of 23 out of 32 RPs from the small ribosomal subunit (SSU) and 32 out of 47 RPs from the large ribosomal subunit (LSU). Ten proteins are partially determined and 14 proteins are missing. Phylogenetic analyses of concatenated RPs from six animals (chaetognath, echinoderm, mammalian, insect, mollusc and sponge) and one fungal taxa do not resolve the chaetognath phylogenetic position, although each mega-sequence comprises approximately 5,000 amino acid residues. This is probably due to the extremely biased base composition and to the high evolutionary rates in chaetognaths. However, the analysis of chaetognath RP genes revealed three unique features in the animal Kingdom. First, whereas generally in animals one RP appeared to have a single type of mRNA, two or more genes are generally transcribed for one RP type in chaetognath. Second, cDNAs with complete 5'-ends encoding a given protein sequence can be divided in two sub-groups according to a short region in their 5'-ends: two novel and highly conserved elements have been identified (5'-TAATTGAGTAGTTT-3' and 5'-TATTAAGTACTAC-3') which could correspond to different transcription factor binding sites on paralog RP genes. And, third, the overall number of deduced paralogous RPs is very high compared to those published for other animals.


CONCLUSIONS
These results suggest that in chaetognaths the deleterious effects of the presence of paralogous RPs, such as apoptosis or cancer are avoided, and also that in each protein family, some of the members could have tissue-specific and extra-ribosomal functions. These results are congruent with the hypotheses of an allopolyploid origin of this phylum and of a ribosome heterogeneity.
Barthélémy
Roxane M
RM
E,R, Biodiversity and environnement, case 5, Pl, V, Hugo, Université de Provence, 13331, Marseille cedex 3, France. Roxane.Barthelemy@univ-provence.fr
Chenuil
Anne
A
Blanquart
Samuel
S
Casanova
Jean-Paul
JP
Faure
Eric
E
D000595:Amino Acid Sequence; D000818:Animals; D018076:DNA, Complementary; D019143:Evolution, Molecular; D020224:Expressed Sequence Tags; D007448:Invertebrates / Q000145:classification / Q000235:genetics*; D010802:Phylogeny; D014176:Protein Biosynthesis; D020033:Protein Isoforms / Q000235:genetics; D012269:Ribosomal Proteins / Q000235:genetics*; D016415:Sequence Alignment
D018076:DNA, Complementary; D020033:Protein Isoforms; D012269:Ribosomal Proteins