ABSTRACT
Xenoturbella bocki has recently been identified as one of the most basal deuterostomes, although an even more basal phylogenetic position cannot be ruled out. Here we report on a polymerase chain reaction survey of partial Hox homeobox sequences of X. bocki. Surprisingly, we did not find evidence for more than five Hox genes, one clear labial/PG1 ortholog, one posterior gene most similar to the PG9/10 genes of Ambulacraria, and three central group genes whose precise assignment to a specific paralog group remains open. We furthermore report on a re-evaluation of the available published evidence of Hox genes in other basal deuterostomes.
Subject(s)
Genes, Homeobox , Invertebrates/genetics , Amino Acid Sequence , Animals , DNA, Ribosomal/genetics , Invertebrates/classification , Multigene Family , PhylogenyABSTRACT
The phylogenetic position of Xenoturbella bocki has been a matter of controversy since its description in 1949. We sequenced a second complete mitochondrial genome of this species and performed phylogenetic analyses based on the amino acid sequences of all 13 mitochondrial protein-coding genes and on its gene order. Our results confirm the deuterostome relationship of Xenoturbella. However, in contrast to a recently published study (Bourlat et al. in Nature 444:85-88, 2006), our data analysis suggests a more basal branching of Xenoturbella within the deuterostomes, rather than a sister-group relationship to the Ambulacraria (Hemichordata and Echinodermata).
Subject(s)
DNA, Mitochondrial/genetics , Invertebrates/genetics , Amino Acid Sequence , Animals , Base Sequence , DNA, Mitochondrial/chemistry , Molecular Sequence Data , Phylogeny , Polymerase Chain Reaction , RNA, Transfer/chemistry , RNA, Transfer/genetics , Sequence AlignmentABSTRACT
Ultrastructural observations of the gastrodermal cells in the enigmatic Xenoturbella revealed numerous chlamydiae. They are related to "Candidatus Fritschea" and Simkania (Simkaniaceae) based on 16S and 23S rRNA. Their 23S rRNA gene contains an intron encoding a putative homing endonuclease. The chlamydiae were pleomorphic and formed intravacuolar colonies. They have flattened disk-shaped elementary bodies, either oval or bow tie-shaped in cross-section, and reticulate bodies that are spherical, polygonal or irregularly shaped. All stages have five-layered cell wall with rippled appearance. Bacteria were not observed in the nuclei. The association between the chlamydiae and Xenoturbella is characterized by absence of cytopathological effects; limited host cell response against the chlamydiae; the confinement of the chlamydiae to inclusions in some part of the host cell; and complete and uniform infection of all examined hosts.
Subject(s)
Chlamydia Infections/physiopathology , Chlamydia/physiology , Chordata, Nonvertebrate/microbiology , Symbiosis/physiology , Animals , Chlamydia/ultrastructure , Genes, rRNA , Microscopy, Electron, Transmission , Phylogeny , RNA, Bacterial/geneticsABSTRACT
Xenoturbella is an enigmatic animal that has puzzled science for almost a century. The eggs and embryos found in Xenoturbella have recently been interpreted as ingested prey. However, PCR on individual eggs as well as in situ hybridisation and in situ PCR unambiguously show that they are Xenoturbella's own. The eggs and embryos are individually enclosed within follicles with the same ultrastructure. The cortical granules in oocytes and eggs from Xenoturbella but not Nucula stained positively with an antiserum against Reissner's substance. The embryos incorporated 5-bromodeoxyuridine in vivo, i.e. they replicate their genome and are living.
