ABSTRACT
The Lower Devonian (Lower Emsian, -400 Myr) roof slates of the Hunsrück in southeastern Germany have delivered a highly diverse and exceptionally preserved marine fauna that provides a unique snapshot into the anatomy and ecology of a wide range of Palaeozoic animals. Several of the described taxa, however, remain enigmatic in their affinity, at least until new pyritized features hidden under the surface of the slate are revealed using X-ray radiography or micro-computed tomography (µCT). Here, we redescribe such an enigmatic fossil, the putative anostracan crustacean Gilsonicaris rhenanus Van Straelen, 1943. Using µCT scanning, we unveil unprecedented details of its anatomy, including a ventral oral opening and four pairs of recalcitrant jaw elements. These jaws are morphologically consistent with the scolecodonts of eunicidan polychaetes, which along with the gross anatomy of the body and head unambiguously identifies G. rhenanus as a polychaete rather than an arthropod. While this discovery firmly discards the Early Devonian record of crown anostracans in the fossil record, it adds a new record of eunicidan soft tissues, which are surprisingly rare considering the abundant microfossil record of scolecodonts.
Subject(s)
Arthropods , Crustacea , Animals , X-Ray Microtomography , Ecology , FossilsABSTRACT
We report the characterization of a caudal gene from the rhizocephalan cirripede Sacculina carcini and its embryonic and larval expression patterns. Cirripedes are maxillopodan crustaceans that are devoid of any complete abdominal segment at the adult stage. We currently explore the genetic basis of this peculiar body plan. In a previous study we have shown that they probably lack the abdominalA gene, while possessing the other Hox genes shared by arthropods. However, at least a part of the genetic program might be conserved, since the engrailed.a and engrailed.b genes are expressed in a posterior region that we interpret as a relic of an ancestral abdomen. Here we show first that the Sacculina caudal gene is expressed early in embryogenesis, which makes it the earliest genetic marker evidenced in the development of Sacculina and of any other crustacean species. It is expressed later in the embryo in the caudal papilla, a posterior proliferating zone of cells. During the larval stages, the caudal gene is first expressed in the whole thoracic region; then its expression regresses to the posterior end of the larva. Surprisingly, it is never expressed in the vestigial abdomen. This lack of expression of the Sacculina caudal gene in a posterior region, at odds with what is known in all other studied metazoan species, might be correlated with the defective development of the abdomen.
Subject(s)
Gene Expression Regulation, Developmental , Homeodomain Proteins/genetics , Thoracica/genetics , Abdomen , Amino Acid Sequence , Animals , Base Sequence , Cloning, Molecular , DNA Primers , DNA, Complementary , Drosophila Proteins , Embryo, Nonmammalian/metabolism , Homeodomain Proteins/chemistry , Larva/metabolism , Molecular Sequence Data , Reverse Transcriptase Polymerase Chain Reaction , Sequence Homology, Amino Acid , Thoracica/embryology , Thoracica/growth & development , Transcription FactorsABSTRACT
The functions of many open reading frames (ORFs) identified in genome-sequencing projects are unknown. New, whole-genome approaches are required to systematically determine their function. A total of 6925 Saccharomyces cerevisiae strains were constructed, by a high-throughput strategy, each with a precise deletion of one of 2026 ORFs (more than one-third of the ORFs in the genome). Of the deleted ORFs, 17 percent were essential for viability in rich medium. The phenotypes of more than 500 deletion strains were assayed in parallel. Of the deletion strains, 40 percent showed quantitative growth defects in either rich or minimal medium.
Subject(s)
Gene Deletion , Genes, Essential , Genome, Fungal , Open Reading Frames , Saccharomyces cerevisiae/genetics , Culture Media , Gene Expression Regulation, Fungal , Gene Targeting , Genes, Fungal , Phenotype , Polymerase Chain Reaction , Recombination, Genetic , Saccharomyces cerevisiae/growth & developmentABSTRACT
Several studies using positron emission tomography with 18F-fluorodeoxyglucose (18F-FDG) have revealed functional hypofrontality in schizophrenia. However, frontal hypometabolism is not consistently found and is not specific to schizophrenia. Basal ganglia glucose hypermetabolism related to neuroleptic treatment has been demonstrated. Methodological and clinical differences between studies are discussed in this paper.
