Receptors for thymosin fraction V on rat thymic lymphocytes

Summary Binding by rat thymus lymphocytes of thymosin V, labeled with colloidal gold, was studied. Under the experimental conditions employed at least 2.8% cells exhibited thymosin binding sites.This article originally appeared in Experientia 38 (5) 1982, p. 618 but was accompanied by imporperfigures. Supported by Polish Academy of SciencesThe authors thank Dr A.L. Goldstein for the gift of thymosin. Also are grateful to Dr J. Jaroszewski for helpful discussion.     

Apoptosis induced by vitamin A signaling is crucial for connecting the ureters to the bladder

Removal of toxic substances from the blood depends on patent connections between the kidney, ureters and bladder that are established when the ureter is transposed from its original insertion site in the male genital tract to the bladder. This transposition is thought to occur as the trigone forms from the common nephric duct and incorporates into the bladder. Here we re-examine this model in the context of normal and abnormal development. We show that the common nephric duct does not differentiate into the trigone but instead undergoes apoptosis, a crucial step for ureter transposition controlled by vitamin A-induced signals from the primitive bladder. Ureter abnormalities occur in 1-2% of the human population and can cause obstruction and end-stage renal disease. These studies provide an explanation for ureter defects underlying some forms of obstruction in humans and redefine the current model of ureter maturation.     

A possible way of origin of parthenogenetic strains ofDinophilus apatris (=D. gyrociliatus)

Riassunto La femmina diD. apatris è fecondata con un numero di spermi spesso insufficiente per tutte le uova che può produrre durante la sua esistenza, per cui le femmine vecchie depongono uova non fecondate che degenerano a stadi di sviluppo diversi. Questa può essere la causa dell'insorgenza di ceppi partenogenetici.     

Regional cyclic AMP levels in homogenates of rat brain after ketalar and trifluoperazine

Summary There was a significant fall in cAMP levels after administration of TFP or ketalar. Different amounts of cAMP were present in different regions of rat brain. Concentrations of cAMP in different regions of the rat brain were found to decrease in the following order: cerebrum > thalamus with hypothalamus > midbrain > hippocampus > cerebral cortex.Conducted under ocntract No 10.4.2 with the Polish Academy of Science.     

Transcriptome analysis of the acoelomate human parasite Schistosoma mansoni

Schistosoma mansoni is the primary causative agent of schistosomiasis, which affects 200 million individuals in 74 countries. We generated 163,000 expressed-sequence tags (ESTs) from normalized cDNA libraries from six selected developmental stages of the parasite, resulting in 31,000 assembled sequences and 92% sampling of an estimated 14,000 gene complement. By analyzing automated Gene Ontology assignments, we provide a detailed view of important S. mansoni biological systems, including characterization of metazoa-specific and eukarya-conserved genes. Phylogenetic analysis suggests an early divergence from other metazoa. The data set provides insights into the molecular mechanisms of tissue organization, development, signaling, sexual dimorphism, host interactions and immune evasion and identifies novel proteins to be investigated as vaccine candidates and potential drug targets.     

Receptors for thymosin fraction V on rat thymic lymphocytes

Summary Binding by rat thymus lymphocytes of thymosin V, labeled with colloidal gold, was studied. Under the experimental conditions employed at least 2.8% cells exhibited thymosin binding sites. Supported by Polish Academy of Sciences. Fellows of Humboldt's Fellowship. The authors thank Dr A.L. Goldstein for the gift of thymosin. Also are grateful to Dr J. Jaroszewski for helpful discussion.     

Structure of Dnmt3a bound to Dnmt3L suggests a model for de novo DNA methylation

Genetic imprinting, found in flowering plants and placental mammals, uses DNA methylation to yield gene expression that is dependent on the parent of origin. DNA methyltransferase 3a (Dnmt3a) and its regulatory factor, DNA methyltransferase 3-like protein (Dnmt3L), are both required for the de novo DNA methylation of imprinted genes in mammalian germ cells. Dnmt3L interacts specifically with unmethylated lysine 4 of histone H3 through its amino-terminal PHD (plant homeodomain)-like domain. Here we show, with the use of crystallography, that the carboxy-terminal domain of human Dnmt3L interacts with the catalytic domain of Dnmt3a, demonstrating that Dnmt3L has dual functions of binding the unmethylated histone tail and activating DNA methyltransferase. The complexed C-terminal domains of Dnmt3a and Dnmt3L showed further dimerization through Dnmt3a-Dnmt3a interaction, forming a tetrameric complex with two active sites. Substitution of key non-catalytic residues at the Dnmt3a-Dnmt3L interface or the Dnmt3a-Dnmt3a interface eliminated enzymatic activity. Molecular modelling of a DNA-Dnmt3a dimer indicated that the two active sites are separated by about one DNA helical turn. The C-terminal domain of Dnmt3a oligomerizes on DNA to form a nucleoprotein filament. A periodicity in the activity of Dnmt3a on long DNA revealed a correlation of methylated CpG sites at distances of eight to ten base pairs, indicating that oligomerization leads Dnmt3a to methylate DNA in a periodic pattern. A similar periodicity is observed for the frequency of CpG sites in the differentially methylated regions of 12 maternally imprinted mouse genes. These results suggest a basis for the recognition and methylation of differentially methylated regions in imprinted genes, involving the detection of both nucleosome modification and CpG spacing.     

Evidence that mechanisms of fin development evolved in the midline of early vertebrates

The origin of paired appendages was a major evolutionary innovation for vertebrates, marking the first step towards fin- (and later limb-) driven locomotion. The earliest vertebrate fossils lack paired fins but have well-developed median fins, suggesting that the mechanisms of fin development were assembled first in the midline. Here we show that shark median fin development involves the same genetic programs that operate in paired appendages. Using molecular markers for different cell types, we show that median fins arise predominantly from somitic (paraxial) mesoderm, whereas paired appendages develop from lateral plate mesoderm. Expression of Hoxd and Tbx18 genes, which specify paired limb positions, also delineates the positions of median fins. Proximodistal development of median fins occurs beneath an apical ectodermal ridge, the structure that controls outgrowth of paired appendages. Each median fin bud then acquires an anteroposteriorly-nested pattern of Hoxd expression similar to that which establishes skeletal polarity in limbs. Thus, despite their different embryonic origins, paired and median fins utilize a common suite of developmental mechanisms. We extended our analysis to lampreys, which diverged from the lineage leading to gnathostomes before the origin of paired appendages, and show that their median fins also develop from somites and express orthologous Hox and Tbx genes. Together these results suggest that the molecular mechanisms for fin development originated in somitic mesoderm of early vertebrates, and that the origin of paired appendages was associated with re-deployment of these mechanisms to lateral plate mesoderm.