Are dendrites in Drosophila homologous to vertebrate dendrites?

Dendrites represent arborising neurites in both vertebrates and invertebrates. However, in vertebrates, dendrites develop on neuronal cell bodies, whereas in higher invertebrates, they arise from very different neuronal structures, the primary neurites, which also form the axons. Is this anatomical difference paralleled by principal developmental and/or physiological differences? We address this question by focussing on one cellular model, motorneurons of Drosophila and characterise the compartmentalisation of these cells. We find that motorneuronal dendrites of Drosophila share with typical vertebrate dendrites that they lack presynaptic but harbour postsynaptic proteins, display calcium elevation upon excitation, have distinct cytoskeletal features, develop later than axons and are preceded by restricted localisation of Par6-complex proteins. Furthermore, we demonstrate in situ and culture that Drosophila dendrites can be shifted from the primary neurite to their soma, i.e. into vertebrate-like positions. Integrating these different lines of argumentation, we propose that dendrites in vertebrates and higher invertebrates have a common origin, and differences in dendrite location can be explained through translocation of neuronal cell bodies introduced during the evolutionary process by which arthropods and vertebrates diverged from a common urbilaterian ancestor. Implications of these findings for studies of dendrite development, neuronal polarity, transport and evolution are discussed.     

REV1 and polymerase ζ facilitate homologous recombination repair

REV1 and DNA Polymerase ζ (REV3 and REV7) play important roles in translesion DNA synthesis (TLS) in which DNA replication bypasses blocking lesions. REV1 and Polζ have also been implicated in promoting repair of DNA double-stranded breaks (DSBs). However, the mechanism by which these two TLS polymerases increase tolerance to DSBs is poorly understood. Here we demonstrate that full-length human REV1, REV3 and REV7 interact in vivo (as determined by co-immunoprecipitation studies) and together, promote homologous recombination repair. Cells lacking REV3 were hypersensitive to agents that cause DSBs including the PARP inhibitor, olaparib. REV1, REV3 or REV7-depleted cells displayed increased chromosomal aberrations, residual DSBs and sites of HR repair following exposure to ionizing radiation. Notably, cells depleted of DNA polymerase η (Polη) or the E3 ubiquitin ligase RAD18 were proficient in DSB repair following exposure to IR indicating that Polη-dependent lesion bypass or RAD18-dependent monoubiquitination of PCNA are not necessary to promote REV1 and Polζ-dependent DNA repair. Thus, the REV1/Polζ complex maintains genomic stability by directly participating in DSB repair in addition to the canonical TLS pathway.     

AMID, an AIF homologous protein, induces caspases-independent apop-tosis

AIF is a mitochondrial flavoprotein that triggers caspase-independent apoptosis. We cloned and characterized a novel AIF homologous molecule designated as AMID (AIF-homologous Mitochondrion-associated Inducer of Death. AMID lacks a mitochondrial localization sequence but shares significant homology with AIF and NADH-oxidoreductases from bacteria to mammalian species. Immunofluorescent staining and biochemical experiments indicated that AMID was co-localized with mitochondria. Overexpression of AMID     

Is malarial anaemia homologous to neocytolysis after altitude acclimatisation?

Malaria patients frequently develop severe anaemia that can persist after Plasmodium infection has been cleared from the circulation. This puzzling phenomenon involves massive death of young uninfected erythrocytes at a time when parasitic infection is very low. We have observed striking similarities in erythrocyte homoeostasis during altitude acclimatisation and Plasmodium infection, both of which initially induce an increase in circulating erythropoietin (Epo). Decreasing levels of Epo after return to low altitudes induce the death of young erythrocytes, a phenomenon called neocytolysis. In a similar way, we propose that Epo, which peaks during acute malaria and decreases after parasite clearance, could be contributing to anaemia causing neocytolysis during recovery from Plasmodium infection.     

Photochemical reactivity of the homologous proteinsα-lactalbumin and lysozyme

Summary The fluorescent behaviour and the photodynamic effect was studied in native and structurally modified lysozyme and-lactalbumin.The Tyr residues in lysozyme and-lactalbumin show different sensitivities to the photodynamic effect. The effect is zero in the case of Tyr from native lysozyme. In contrast, the Tyr residues in-lactalbumin are susceptible to photooxidation, which indicates a greater degree of exposure to the solvent. The three His residues of-lactalbumin have different degrees of exposure and show two different kinetics of photooxidation whereas the His residue of lysozyme is photooxidized with a single kinetic.Two photooxidation kinetics were obtained for the Trp residues of both native proteins, an indication that in both cases there are Trp residues that are differently exposed to the solvent. The wavelengths of maximum fluorescent emission of the Trp residues were different for the two proteins, an effect which can also be explained in terms of a difference in the environment of these residues. The modified form of these proteins emit at wavelengths longer than those of the native forms. When modified the proteins photooxidize with noticeably greater quantum yields.     

Rad54: the Swiss Army knife of homologous recombination?

Homologous recombination (HR) is a ubiquitous cellular pathway that mediates transfer of genetic information between homologous or near homologous (homeologous) DNA sequences. During meiosis it ensures proper chromosome segregation in the first division. Moreover, HR is critical for the tolerance and repair of DNA damage, as well as in the recovery of stalled and broken replication forks. Together these functions preserve genomic stability and assure high fidelity transmission of the genetic material in the mitotic and meiotic cell divisions. This review will focus on the Rad54 protein, a member of the Snf2-family of SF2 helicases, which translocates on dsDNA but does not display strand displacement activity typical for a helicase. A wealth of genetic, cytological, biochemical and structural data suggests that Rad54 is a core factor of HR, possibly acting at multiple stages during HR in concert with the central homologous pairing protein Rad51.     

Time to match; when do homologous chromosomes become closer?

Chromosoma - In most eukaryotes, pairing of homologous chromosomes is an essential feature of meiosis that ensures homologous recombination and segregation. However, when the pairing process...     

Amyloidogenic peptide homologous to fragment 129–148 of human myocilin

Myocilin is a protein with a molecular weight near 50 kDa. It is expressed in almost all organs and tissues.¹ We showed that the peptide DQL ETQ TRE LET AYS NLL RD corresponding to N-terminal Leucine zipper motif (LZM) of the protein is able to form amyloid-like fibrils. The possible role of this motif in myocilin aggregation is discussed.     

Is it possible to improve homologous recombination in Chlamydomonas reinhardtii?

Targeted modification of the genome has long been an aim of many geneticists and biotechnologists. Gene targeting is a main molecular tool to examine biological effects of genes in a controlled environment. Effective gene targeting depends on the frequency of homologous recombination that is indispensable for the insertion of foreign DNA into a specific sequence of the genome. The main problem associated with the development of an optimal procedure for gene targeting in a particular organism is the variability of homologous recombination (HR) in different species. Chlamydomonas reinhardtii is an attractive model system for the study of many cellular processes and is also an interesting object for the biotechnology industry. In spite of many advantages of this model system, C. reinhardtii does not readily express heterologous genes and does not allow targeted integration of foreign DNA into its genome easily. This paper compares data obtained from several different experiments designed for improving gene targeting in different organisms and reviews the suitability of particular techniques in C. reinhardtii cells. Presented at the International Symposium Biology and Taxonomy of Green Algae V, Smolenice, June 26–29, 2007, Slovakia.     

Genes for two homologous G-protein α subunits map to different human chromosomes

Summary Signal transduction across biological membranes is modulated by a family of related GTP-binding proteins termed G proteins. These G proteins have a heterotrimeric structure composed of α, β, and γ subunits. The α subunits of the G proteins bind GTP and appear to determine the biochemical specificity of the protein. We have recently cloned and characterized cDNA encoding two G-protein α subunits, α_i and α_h. The former is a substrate for ADP-ribosylation by pertussis toxin. The protein corresponding to α_h has not yet been identified. These cDNAs encode proteins, which demonstrate 90% sequence identity to one another and also show marked similarity to other G proteins. The present studies were designed to determine whether the genes for these related proteins are clustered on a single human chromosome. Genomic DNA isolated from a panel of mouse-human hybrid cell lines was analyzed by hybridization to cDNAs for α_i and α_h. Based on the distribution patterns of α_i and α_h in cell hybrids, the gene for α_i was assigned to human chromosome 7, and the gene for α_h assigned to chromosome 12. These data suggest that the G-protein gene family may be distributed over at least two human chromosomes.     

Can recA protein promote homologous pairing between duplex regions of DNA?

RecA protein has been shown to promote the formation of joint molecules between intact duplex DNA and homologous gapped DNA. When examined by electron microscopy, such joint molecules display a junction that is, in most cases, distant from the site of the gap. This led us to test whether the observed location of the joint was due to pairing at the gap followed by branch migration, or whether recA-promoted pairing could also take place between duplex homologous regions away from the gap. To test the latter possibility, intact duplex DNA was incubated with DNA which contained a gap in a region of non-homology. Joint molecules were detected by filter binding assay and by electron microscopy at about one-third of the yield observed for fully homologous molecules. These results indicate that initial homologous pairing promoted by recA protein is not restricted to the single-stranded region in the gap but can also take place in regions where both molecules are duplex.     

Three homologous genes encoding functional ∆8-sphingolipid desaturase in Populus tomentosa

?⁸-sphingolipid desaturase is characterized by its ability to catalyze desaturation at the C8 position of the long-chain base of sphingolipids in plants. No previous studies have been conducted on genes encoding Δ⁸-sphingolipid desaturases in the woody plant Populus tomentosa. In this study, three genes that encode Δ⁸-sphingolipid desaturase were isolated from P. tomentosa. Among these genes, PtD8A and PtD8B showed high sequence similarity; whereas PtD8C exhibited large sequence divergence. RT-PCR results showed that PtD8A and PtD8B were expressed in all tissues detected, whereas PtD8C was not expressed in roots. Heterologous expression in yeast revealed that PtD8A/B/C were functional Δ⁸-sphingolipid desaturases, and can catalyze the C18-phytosphingenine desaturation to produce 8(Z)- and 8(E)-C18-phytosphingenine. However, the conversion rate and ratios of the two products differed. Compared with control cells, transgenic yeasts expressing PtD8A/B/C exhibited enhanced aluminum tolerance. Our findings further elucidated the biochemical functions and evolutionary history of Δ⁸-sphingolipid desaturases in plants. Candidate genes for breeding new poplar germplasm resources with enhanced tolerance ability to aluminium were also provided.     

Finding a match: how do homologous sequences get together for recombination?

Decades of research into homologous recombination have unravelled many of the details concerning the transfer of information between two homologous sequences. By contrast, the processes by which the interacting molecules initially colocalize are largely unknown. How can two homologous needles find each other in the genomic haystack? Is homologous pairing the result of a damage-induced homology search, or is it an enduring and general feature of the genomic architecture that facilitates homologous recombination whenever and wherever damage occurs? This Review presents the homologous-pairing enigma, delineates our current understanding of the process and offers guidelines for future research.     

Analyzing variable behavioral contingencies: Are certain complex skills homologous with locomotion?

This paper considers behavioral contingencies that change as a function of time, of the individual's own behavior (as in locomotion and reading), of the behavior of other parties or of interactions with them. A detailed analysis of locomotion and of reading out loud shows that the behavioral contingencies for these are virtually the same. The terrain being traversed and the locomotion behavior involved are shown to be analogous to a segment of text being read and the articulation of the words. In both cases, successive upcoming segments are perceived and processed, and during the processing phases, motor behavior is formulated. In both, the smooth concatenation of the motor phases for successive segments requires buffering. Both involve corrective or digressive actions in response to obstacles or unanticipated stimuli encountered. Both involve looking ahead at the upcoming segment and processing it while the motor phase of the prior segment is still in progress. For both, the size, entropy, familiarity, and other attributes of the upcoming segment are parameters of the performance. It is suggested that locomotion has similar parallels with certain other complex skills, such as listening, copying, receiving Morse code, simultaneous interpreting, and certain types of performance, and may therefore be their phylogenetic prototype and biological homologue.