Development of myelination and axon diameter for fast and precise action potential conductance

Axons of globular bushy cells in the cochlear nucleus convey hyper-accurate signals to the superior olivary complex, the initial site of binaural processing via comparably thick axons and the calyx of the Held synapse. Bushy cell fibers involved in hyper-accurate binaural processing of low-frequency sounds are known to have an unusual internode length-to-axon caliber ratio (L/d) correlating with higher conduction velocity and superior temporal precision of action potentials. How the L/d-ratio develops and what determines this unusual myelination pattern is unclear. Here we describe a gradual developmental transition from very simple to complex, mature nodes of Ranvier on globular bushy cell axons during a 2-week period starting at postnatal day P6/7. The molecular composition of nodes matured successively along the axons from somata to synaptic terminals with morphologically and molecularly mature nodes appearing almost exclusively after hearing onset. Internodal distances are initially coherent with the canonical L/d-ratio of ~100. Several days after hearing onset, however, an over-proportional increase in axon caliber occurs in cells signaling low-frequency sounds which alters their L/d ratio to ~60. Hence, oligodendrocytes initially myelinating axons according to their transient axon caliber but a subsequent differential axon thickening after hearing onset results in the unusual myelination pattern.

A new look at the architecture and dynamics of the Hydra nerve net

The Hydra nervous system is the paradigm of a 'simple nerve net'. Nerve cells in Hydra, as in many cnidarian polyps, are organized in a nerve net extending throughout the body column. This nerve net is required for control of spontaneous behavior: elimination of nerve cells leads to polyps that do not move and are incapable of capturing and ingesting prey (Campbell, 1976). We have re-examined the structure of the Hydra nerve net by immunostaining fixed polyps with a novel antibody that stains all nerve cells in Hydra. Confocal imaging shows that there are two distinct nerve nets, one in the ectoderm and one in the endoderm, with the unexpected absence of nerve cells in the endoderm of the tentacles. The nerve nets in the ectoderm and endoderm do not contact each other. High-resolution TEM (transmission electron microscopy) and serial block face SEM (scanning electron microscopy) show that the nerve nets consist of bundles of parallel overlapping neurites. Results from transgenic lines show that neurite bundles include different neural circuits and hence that neurites in bundles require circuit-specific recognition. Nerve cell-specific innexins indicate that gap junctions can provide this specificity. The occurrence of bundles of neurites supports a model for continuous growth and differentiation of the nerve net by lateral addition of new nerve cells to the existing net. This model was confirmed by tracking newly differentiated nerve cells.

A Case for Electron-Astrophysics

The smallest characteristic scales, at which electron dynamics determines the plasma behaviour, are the next frontier in space and astrophysical plasma research. The analysis of astrophysical processes at these scales lies at the heart of the research theme of electron-astrophysics. Electron scales are the ultimate bottleneck for dissipation of plasma turbulence, which is a fundamental process not understood in the electron-kinetic regime. In addition, plasma electrons often play an important role for the spatial transfer of thermal energy due to the high heat flux associated with their velocity distribution. The regulation of this electron heat flux is likewise not understood. By focussing on these and other fundamental electron processes, the research theme of electron-astrophysics links outstanding science questions of great importance to the fields of space physics, astrophysics, and laboratory plasma physics. In this White Paper, submitted to ESA in response to the Voyage 2050 call, we review a selection of these outstanding questions, discuss their importance, and present a roadmap for answering them through novel space-mission concepts.

Spectrum of kinetic plasma turbulence at 0.3-0.9 astronomical units from the Sun

We investigate spectral properties of turbulence in the solar wind that is a weakly collisional astrophysical plasma, accessible to in situ observations. Using the Helios search coil magnetometer measurements in the fast solar wind, in the inner heliosphere, we focus on properties of the turbulent magnetic fluctuations at scales smaller than the ion characteristic scales, the so-called kinetic plasma turbulence. At such small scales, we show that magnetic power spectra between 0.3 and 0.9 AU from the Sun have a generic shape ∼f^{-8/3}exp(-f/f_{d}), where the dissipation frequency f_{d} is correlated with the Doppler shifted frequency f_{ρe} of the electron Larmor radius. This behavior is statistically significant: all the observed kinetic spectra are well described by this model, with f_{d}=f_{ρe}/1.8. Our results indicate that the electron gyroradius plays the role of the dissipation scale and marks the end of the electromagnetic cascade in the solar wind.

Women who inject drugs in Russia: stigma as a barrier in access to HIV and drug treatment services

Background

There are over one million people living with HIV in Russia. People who inject drugs experience major disparities in their susceptibility to the virus and in their access to HIV services. Women who inject drugs (WWID) have been shown to be at heightened susceptibility to HIV, through both unsafe drug use and unprotected sex. Less is known about the social determinants of engagement in care specifically among WWID.

Methods

We conducted a qualitative research study in St. Petersburg in order to assess what factors influence engagement in HIV-related and drug rehabilitation services. We conducted in-depth interviews with 20 service providers and 30 WWID from June-November 2018. We recruited providers to represent a range of services, including government clinics, non-governmental organizations, and family services. We recruited WWID through community outreach services. We used thematic analysis and a team-based approach to coding data.

Results

A major theme across our data was the stigma and discrimination that WWID experience in their everyday lives and in their interactions with the healthcare system. WWID are subjected to stigmatization related to gender norms about drug use, the capacity to fulfill their roles as mothers, (for some) engagement in sex work, and (for some) HIV-positive serostatus. WWID are often reluctant to seek HIV-related services, including testing and treatment, out of fear of being treated poorly because of their drug use. The omnipresent societal stigma manifests into self-stigmatization and many WWID questioned their deserving of and abilities to seek healthcare services, including drug rehabilitation and HIV-related care.

Conclusions

Interventions are needed to address the stigma and discrimination that WWID in Russia experience in families, communities, and health institutions. Additionally, psychosocial interventions may help to address the self-stigmatization that sometimes influences WWID's self-efficacy to seek services.

The role of rehabilitation and educational institutions in vocational training and employment of people with disabilities

The article presents some results of a comprehensive sociological research carried out in Moscow in 2018, the purpose of which was to identify the main problems facing people with disabilities (with various types of persistent disorders of body functions) in the capital’s labor market. On the basis of a series of in-depth structured interviews with experts from institutions related to the training and employment of people with disabilities, conclusions were drawn about the features of the selection of vacancies and the problems of adaptation of people with disabilities in the Moscow labor market. The interest of employers in the organization of jobs for persons with disabilities is considered as one of the key issues. One of the issues discussed is the choice between the expediency of creating jobs in the framework of specialized enterprises of the disabled and their integration into the work of ordinary enterprises. Approaches to this issue in different countries have their own characteristics and are determined by the attitude in society towards a person in general and towards a disabled person in particular. The problem of the perception of persons with disabilities in educational institutions and working collectives is considered, and the specific of adaptation of persons with disabilities to digital economy are discussed. There are highlighted the features inherent to social appearance of people with disabilities, as potential employees, as well as the influence of the immediate environment, a kind of ecosystem of a disabled person, on his motivation to work. The social profile of disabled person outlines five key positions in terms of both internal attitudes and environmental conditions affecting employment. In modern conditions of digitalization of the economy, the issues of adaptation of disabled people to its specific features are considered. The authors highlight the role of rehabilitation and special educational institutions in Moscow in preparation of persons with disabilities to their work activities, the ability to present themselves in the selection of a suitable vacancy and the expansion of opportunities to implement their work plans.

Urocortin 3 signalling in the auditory brainstem aids recovery of hearing after reversible noise-induced threshold shift

KEY POINTS

Ongoing, moderate noise exposure does not instantly damage the auditory system but may cause lasting deficits, such as elevated thresholds and accelerated ageing of the auditory system. The neuromodulatory peptide urocortin-3 (UCN3) is involved in the body's recovery from a stress response, and is also expressed in the cochlea and the auditory brainstem. Lack of UCN3 facilitates age-induced hearing loss and causes permanently elevated auditory thresholds following a single 2 h noise exposure at moderate intensities. Outer hair cell function in mice lacking UCN3 is unaffected, so that the observed auditory deficits are most likely due to inner hair cell function or central mechanisms. Highly specific, rather than ubiquitous, expression of UCN3 in the brain renders it a promising candidate for designing drugs to ameliorate stress-related auditory deficits, including recovery from acoustic trauma.

ABSTRACT

Environmental acoustic noise is omnipresent in our modern society, with sound levels that are considered non-damaging still causing long-lasting or permanent changes in the auditory system. The small neuromodulatory peptide urocortin-3 (UCN3) is the endogenous ligand for corticotropin-releasing factor receptor type 2 and together they are known to play an important role in stress recovery. UCN3 expression has been observed in the auditory brainstem, but its role remains unclear. Here we describe the detailed distribution of UCN3 expression in the murine auditory brainstem and provide evidence that UCN3 is expressed in the synaptic region of inner hair cells in the cochlea. We also show that mice with deficient UCN3 signalling experience premature ageing of the auditory system starting at an age of 4.7 months with significantly elevated thresholds of auditory brainstem responses (ABRs) compared to age-matched wild-type mice. Following a single, 2 h exposure to moderate (84 or 94 dB SPL) noise, UCN3-deficient mice exhibited significantly larger shifts in ABR thresholds combined with maladaptive recovery. In wild-type mice, the same noise exposure did not cause lasting changes to auditory thresholds. The presence of UCN3-expressing neurons throughout the auditory brainstem and the predisposition to hearing loss caused by preventing its normal expression suggests UCN3 as an important neuromodulatory peptide in the auditory system's response to loud sounds.

Local approach to the study of energy transfers in incompressible magnetohydrodynamic turbulence

We present a local approach to the study of scale-to-scale energy transfers in magnetohydrodynamic (MHD) turbulence. This approach is based on performing local averages of the physical fields, which amounts to filtering scales smaller than some parameter ℓ. A key step in this work is the derivation of a local Kármán-Howarth-Monin relation which provides a local form of Politano and Pouquet's 4/3 law, without any assumption of homogeneity or isotropy. Our approach is exact and nonrandom, and we show its connection to the usual statistical results of turbulence. Its implementation on data obtained via a three-dimensional direct numerical simulation of the forced incompressible MHD equations from the John Hopkins turbulence database constitutes the main part of our study. First, we show that the local Kármán-Howarth-Monin relation holds well. The space statistics of local cross-scale transfers are studied next, their means and standard deviations being maximum at inertial scales and their probability density functions (PDFs) displaying very wide tails. Events constituting the tails of the PDFs are shown to form structures of strong transfers, either positive or negative, which can be observed over the whole available range of scales. As ℓ is decreased, these structures become more and more localized in space while contributing to an increasing fraction of the mean energy cascade rate. Finally, we highlight their quasi-one-dimensional (filamentlike) or quasi-two-dimensional (sheetlike or ribbonlike) nature and show that they appear in areas of strong vorticity or electric current density.

Healthcare reform: Heads of medical organizations at the forefront of problems

The article is devoted to the impact of healthcare reform on the situation in the industry and the requirements for managers of medical organizations. On the data from the expert survey, participants of which were physicians with practical experience in the field of health management; economists studying the work of the public sector; lawyers involved in the protection of patients’ rights, etc., it provides characteristics of today’s financial, logistical support and staffing of medical institutions, their relationships with founders, insurance companies and patients; there are given experts’ opinions on who should be the leaders of medical organizations — managers or clinicians, how to create their personnel reserve, what should be changed in the system of professional development and retraining of medical personnel. It is shown that the working conditions of medical organizations have radically changed, and the amount of attracted extra-budgetary funds has become an important indicator of their effectiveness. At the same time, the institutional context, in which they function, is highly controversial, devoid of a number of fundamentally important elements, and is not balanced in terms of the rights and obligations of various actors involved in the provision of medical care. This significantly complicates the activity of the management of medical institutions, generates a «conflict of interests» among them, which ultimately negatively affects patients. According to experts, today an experienced manager should be at the head of the medical institution, but — with the obligatory good knowledge and understanding of the specifics of the medical industry. Since medical institutions are now managed by medics, their training in economics and management within the system of continuing professional education becomes very important. The article is divided into two parts. The second part will be published in Population 2019 No.1.

Physiology and anatomy of neurons in the medial superior olive of the mouse

In mammals with good low-frequency hearing, the medial superior olive (MSO) computes sound location by comparing differences in the arrival time of a sound at each ear, called interaural time disparities (ITDs). Low-frequency sounds are not reflected by the head, and therefore level differences and spectral cues are minimal or absent, leaving ITDs as the only cue for sound localization. Although mammals with high-frequency hearing and small heads (e.g., bats, mice) barely experience ITDs, the MSO is still present in these animals. Yet, aside from studies in specialized bats, in which the MSO appears to serve functions other than ITD processing, it has not been studied in small mammals that do not hear low frequencies. Here we describe neurons in the mouse brain stem that share prominent anatomical, morphological, and physiological properties with the MSO in species known to use ITDs for sound localization. However, these neurons also deviate in some important aspects from the typical MSO, including a less refined arrangement of cell bodies, dendrites, and synaptic inputs. In vitro, the vast majority of neurons exhibited a single, onset action potential in response to suprathreshold depolarization. This spiking pattern is typical of MSO neurons in other species and is generated from a complement of K_v1, K_v3, and I_H currents. In vivo, mouse MSO neurons show bilateral excitatory and inhibitory tuning as well as an improvement in temporal acuity of spiking during bilateral acoustic stimulation. The combination of classical MSO features like those observed in gerbils with more unique features similar to those observed in bats and opossums make the mouse MSO an interesting model for exploiting genetic tools to test hypotheses about the molecular mechanisms and evolution of ITD processing.

Tuning of Ranvier node and internode properties in myelinated axons to adjust action potential timing

Action potential timing is fundamental to information processing; however, its determinants are not fully understood. Here we report unexpected structural specializations in the Ranvier nodes and internodes of auditory brainstem axons involved in sound localization. Myelination properties deviated significantly from the traditionally assumed structure. Axons responding best to low-frequency sounds had a larger diameter than high-frequency axons but, surprisingly, shorter internodes. Simulations predicted that this geometry helps to adjust the conduction velocity and timing of action potentials within the circuit. Electrophysiological recordings in vitro and in vivo confirmed higher conduction velocities in low-frequency axons. Moreover, internode length decreased and Ranvier node diameter increased progressively along the distal axon segments, which simulations show was essential to ensure precisely timed depolarization of the giant calyx of Held presynaptic terminal. Thus, individual anatomical parameters of myelinated axons can be tuned to optimize pathways involved in temporal processing.

Action potential timing is fundamental to information processing, but its determinants are not fully understood. Here the authors demonstrate unexpected structural specializations of myelinated axons in the auditory brainstem that help to adjust action potential arrival time for sound localization.

Adaptation in sound localization: from GABA(B) receptor-mediated synaptic modulation to perception

Across all sensory modalities, the effect of context-dependent neural adaptation can be observed at every level, from receptors to perception. Nonetheless, it has long been assumed that the processing of interaural time differences, which is the primary cue for sound localization, is nonadaptive, as its outputs are mapped directly onto a hard-wired representation of space. Here we present evidence derived from in vitro and in vivo experiments in gerbils indicating that the coincidence-detector neurons in the medial superior olive modulate their sensitivity to interaural time differences through a rapid, GABA(B) receptor-mediated feedback mechanism. We show that this mechanism provides a gain control in the form of output normalization, which influences the neuronal population code of auditory space. Furthermore, psychophysical tests showed that the paradigm used to evoke neuronal GABA(B) receptor-mediated adaptation causes the perceptual shift in sound localization in humans that was expected on the basis of our physiological results in gerbils.

Anisotropy of solar wind turbulence between ion and electron scales

The anisotropy of turbulence in the fast solar wind, between the ion and electron gyroscales, is directly observed using a multispacecraft analysis technique. Second order structure functions are calculated at different angles to the local magnetic field, for magnetic fluctuations both perpendicular and parallel to the mean field. In both components, the structure function value at large angles to the field S{⊥} is greater than at small angles S{∥}: in the perpendicular component S{⊥}/S{∥}=5±1 and in the parallel component S{⊥}/S{∥}>3, implying spatially anisotropic fluctuations, k{⊥}>k{∥}. The spectral index of the perpendicular component is -2.6 at large angles and -3 at small angles, in broad agreement with critically balanced whistler and kinetic Alfvén wave predictions. For the parallel component, however, it is shallower than -1.9, which is considerably less steep than predicted for a kinetic Alfvén wave cascade.

Universality of solar-wind turbulent spectrum from MHD to electron scales

To investigate the universality of magnetic turbulence in space plasmas, we analyze seven time periods in the free solar wind under different plasma conditions. Three instruments on Cluster spacecraft operating in different frequency ranges give us the possibility to resolve spectra up to 300 Hz. We show that the spectra form a quasiuniversal spectrum following the Kolmogorov's law approximately k(-5/3) at MHD scales, a approximately k(-2.8) power law at ion scales, and an exponential approximately exp[-sqrt[k(rho)e]] at scales k(rho)e approximately [0.1,1], where rho(e) is the electron gyroradius. This is the first observation of an exponential magnetic spectrum in space plasmas that may indicate the onset of dissipation. We distinguish for the first time between the role of different spatial kinetic plasma scales and show that the electron Larmor radius plays the role of a dissipation scale in space plasma turbulence.

Experience-dependent refinement of the inhibitory axons projecting to the medial superior olive

Neurons in the medial superior olive (MSO) analyze interaural time differences (ITDs) by comparing the arrival times of the two excitatory inputs from each ear using a coincidence detection mechanism. They also receive a prominent inhibitory, glycinergic projection from the ipsilateral medial nucleus of the trapezoid body (MNTB), which contributes to the fine-tuning of ITD analysis. Here, we investigated developmental changes of the axonal arborisation pattern of single Microruby-labeled MNTB neurons projecting to the MSO region. During the first 2 weeks after hearing onset, the axonal arborisation of MNTB neurons was significantly refined resulting in a narrowed projection area across the tonotopic axis of the MSO and a redistribution of the axonal endsegments to a mostly somatic location. Rearing the animals in omnidirectional noise prevented the structural changes of single MNTB projections. These results indicate that the functional elimination of inhibitory inputs on MSO neurons after hearing onset, as described previously, is paralleled by a structural, site-specific refinement of the inputs and is dependent on the normal acoustic experience of the animal.

Programmed cell death in Hydra

Hydra is one of the simplest metazoans and thus an important model organism for studies on the evolution of developmental mechanisms in multi-cellular animals. In Hydra apoptosis is involved in the regulation of cell numbers in response to feeding, in regeneration and in the removal of non-self cells. It also participates in the maintenance of cellular homeostasis in germ cells. During oogenesis a special "arrested" apoptosis of nurse cells is observed. The morphology of apoptotic hydra cells is almost indistinguishable from apoptosis in higher animals and caspases as well as members of the Bcl-2 family participate in the process.

The Notch signaling pathway in the cnidarian Hydra

Many of the major pathways that govern early development in higher animals have been identified in cnidarians, including the Wnt, TGFbeta and tyrosine kinase signaling pathways. We show here that Notch signaling is also conserved in these early metazoans. We describe the Hydra Notch receptor (HvNotch) and provide evidence for the conservation of the Notch signaling mode via regulated intramembrane proteolysis. We observed that nuclear translocation of the Notch intracellular domain (NID) was inhibited by the synthetic gamma-secretase inhibitor DAPT. Moreover, DAPT treatment of hydra polyps caused distinct differentiation defects in their interstitial stem cell lineage. Nerve cell differentiation proceeded normally but post-mitotic nematocyte differentiation was dramatically reduced. Early female germ cell differentiation was inhibited before exit from mitosis. From these results we conclude that gamma-secretase activity and presumably Notch signaling are required to control differentiation events in the interstitial cell lineage of Hydra.

Genetic screen for signal peptides in Hydra reveals novel secreted proteins and evidence for non-classical protein secretion

We have screened a Hydra cDNA library for sequences encoding N-terminal signal peptides using the yeast invertase secretion vector pSUC [Jacobs et al., 1997. A genetic selection for isolating cDNAs encoding secreted proteins. Gene 198, 289-296]. We isolated and sequenced 907 positive clones; 88% encoded signal peptides; 12% lacked signal peptides. By searching the Hydra EST database we identified full-length sequences for the selected clones. These encoded 37 known proteins with signal peptides and 40 novel Hydra-specific proteins with signal peptides. Localization of two signal peptide-containing sequences, VEGF and ferritin, to the secretory pathway was confirmed with GFP fusion proteins. In addition, we isolated 105 clones which lacked signal peptides but which supported invertase secretion from yeast. Isolation of plasmids from these clones and retransformation in invertase-negative yeast cells confirmed the phenotype. A GFP fusion protein of one such clone encoding the foot morphogen pedibin was localized to the cytoplasm in transfected Hydra cells and did not enter the ER/Golgi secretory pathway. Secretion of pedibin and other proteins lacking signal peptides appears to occur by a non-classical protein secretion route.

Synthesis of pre-rRNA and mRNA is directed to a chromatin-poor compartment in the macronucleus of the spirotrichous ciliate Stylonychia lemnae

In contrast to the chromosomal genome organization common to most eukaryotes, DNA in the macronucleus of spirotrichous ciliates like Stylonychia lemnae is organized into small gene-sized nanochromosomes. We intended to elucidate whether a spatial organization of nucleoli similar to other eukaryotes can be found in absence of typical chromosomes. Whereas micronuclei of Stylonychia exhibit homogenously stained heterochromatin and possess no nucleoli, macronuclear chromatin is compartmentalized and contains numerous putative nucleoli. Since the identity of these spherical structures has never been unequivocally demonstrated to date, we applied immunofluorescence techniques together with confocal laser scanning microscopy to identify nucleolar bodies in the macronucleus of Stylonychia and to analyse their spatial organization. We found that multiple spherical bodies, which fulfil nucleolar function, occupy a peripheral localization in mature macronuclei. Using fibrillarin/Nop1p as a nucleolar marker, we monitored the assembly of such nucleolar bodies during macronuclear differentiation. 3D-FISH experiments revealed that rRNA genes are mostly concentrated adjacent to but not inside of fibrillarin/Nop1p-containing bodies. We further showed that transcription sites for rRNA synthesis but also for mRNA synthesis occur predominantly at surfaces of nucleolar bodies and chromatin-poor spaces bordering condensed chromatin. Our data suggest that transcription of rRNA genes in the macronucleus of Stylonychia does not rely on a classical nucleolus-type organization. We assume that vectorial synthesis and processing of rRNA and mRNA is directed to a functional interchromatin compartment.

Exploiting nuclear duality of ciliates to analyse topological requirements for DNA replication and transcription

Spatial and temporal replication patterns are used to describe higher-order chromatin organisation from nuclei of early metazoan to mammalian cells. Here we demonstrate evolutionary conserved similarities and differences in replication patterns of micronuclei and macronuclei in the spirotrichous ciliate Stylonychia lemnae. Since this organism possesses two kinds of morphologically and functionally different nuclei in one cell, it provides an excellent model system to analyse topological requirements for DNA replication and transcription. Replication in the heterochromatic micronucleus occurs in foci-like structures showing spatial and temporal patterns similar to nuclei of higher eukaryotes, demonstrating that these patterns are inherent features of nuclear architecture. The 'nanochromosomes' of the macronucleus are replicated in the propagating replication band. We show that it consists of hundreds of replication foci. Post-replicative macronuclear chromatin remains organised in foci. These foci are not randomly distributed throughout the macronucleus, indicating a higher-order organisation of macronuclear chromatin above the level of 'nanochromosomes'. Both telomerase and proliferating cell nuclear antigen (PCNA) occur as foci-like structures in the rear zone of the replication band, suggesting that a wave of chromatin modification driven by a short or continuous exogenous signal permits the assembly of replication factories at predicted sites. We further show that transcription occurs at discrete sites colocalised with putative nucleoli and dispersed chromatin. Common principles of functional nuclear architecture were conserved during eukaryotic evolution. Moreover nuclear duality inherent to ciliates with their germline micronucleus and their somatic macronucleus may eventually provide further insight into epigenetic regulation of transcription, replication and nuclear differentiation.

Oogenesis in Hydra: Nurse cells transfer cytoplasm directly to the growing oocyte

Oogenesis in Hydra occurs in so-called egg patches containing several thousand germ cells. Only one oocyte is formed per egg patch; the remaining germ cells differentiate as nurse cells. Whether and how nurse cells contribute cytoplasm to the developing oocyte has been unclear. We have used tissue maceration to characterize the differentiation of oocytes and nurse cells in developing egg patches. We show that nurse cells decrease in size at the same time that developing oocytes increase dramatically in volume. Nurse cells are also tightly attached to oocytes at this stage and confocal images of egg patches stained with the fluorescent membrane dye FM 4-64 clearly show large gaps (10 microm) in the cell membranes separating nurse cells from the developing oocyte. We conclude that nurse cells directly transfer cytoplasm to the developing oocyte. Following this transfer of cytoplasm, nurse cells undergo apoptosis and are phagocytosed by the oocyte. These results demonstrate that basic mechanisms of alimentary oogenesis typical of Caenorhabditis and Drosophila are already present in the early metazoan Hydra.

The phosphatidylserine receptor from Hydra is a nuclear protein with potential Fe(II) dependent oxygenase activity

BACKGROUND

Apoptotic cell death plays an essential part in embryogenesis, development and maintenance of tissue homeostasis in metazoan animals. The culmination of apoptosis in vivo is the phagocytosis of cellular corpses. One morphological characteristic of cells undergoing apoptosis is loss of plasma membrane phospholipid asymmetry and exposure of phosphatidylserine on the outer leaflet. Surface exposure of phosphatidylserine is recognised by a specific receptor (phosphatidylserine receptor, PSR) and is required for phagocytosis of apoptotic cells by macrophages and fibroblasts.

RESULTS

We have cloned the PSR receptor from Hydra in order to investigate its function in this early metazoan. Bioinformatic analysis of the Hydra PSR protein structure revealed the presence of three nuclear localisation signals, an AT-hook like DNA binding motif and a putative 2-oxoglutarate (2OG)-and Fe(II)-dependent oxygenase activity. All of these features are conserved from human PSR to Hydra PSR. Expression of GFP tagged Hydra PSR in hydra cells revealed clear nuclear localisation. Deletion of one of the three NLS sequences strongly diminished nuclear localisation of the protein. Membrane localisation was never detected.

CONCLUSIONS

Our results suggest that Hydra PSR is a nuclear 2-oxoglutarate (2OG)-and Fe(II)-dependent oxygenase. This is in contrast with the proposed function of Hydra PSR as a cell surface receptor involved in the recognition of apoptotic cells displaying phosphatidylserine on their surface. The conservation of the protein from Hydra to human infers that our results also apply to PSR from higher animals.

Replication labeling patterns and chromosome territories typical of mammalian nuclei are conserved in the early metazoan Hydra

To investigate the evolutionary conservation of higher order nuclear architecture previously described for mammalian cells we have analyzed the nuclear architecture of the simple polyp Hydra. These diploblastic organisms have large nuclei (8-10 microm) containing about 3x10(9) bp of DNA organized in 15 chromosome pairs. They belong to the earliest metazoan phylum and are separated from mammals by at least 600 million years. Single and double pulse labeling with halogenated nucleotides (bromodeoxyuridine, iododeoxyuridine and chlorodeoxyuridine) revealed striking similarities to the known sequence of replication labeling patterns in mammalian nuclei. These patterns reflect a persistent nuclear arrangement of early, mid-, and late replicating chromatin foci that could be identified during all stages of interphase over at least 5-10 cell generations. Segregation of labeled chromatids led after several cell divisions to nuclei with single or a few labeled chromosome territories. In such nuclei distinct clusters of labeled chromatin foci were separated by extended nuclear areas with non-labeled chromatin, which is typical of a territorial arrangement of interphase chromosomes. Our results indicate the conservation of fundamental features of higher order chromatin arrangements throughout the evolution of metazoan animals and suggest the existence of conserved mechanism(s) controlling this architecture.

Molecular cloning and cellular distribution of two 14-3-3 isoforms from Hydra: 14-3-3 proteins respond to starvation and bind to phosphorylated targets

In the simple metazoan Hydra a clear link between food supply and cell survival has been established. Whilst in plants 14-3-3 proteins are found to be involved in signalling cascades that regulate metabolism, in animals they have been shown to participate in cell survival pathways. In order to explore the possibility that 14-3-3 proteins in Hydra could be involved in regulating metabolism under different conditions of food supply, we have cloned two isoforms of 14-3-3 proteins. We show here that 14-3-3 proteins bind to phosphorylated targets in Hydra and form homo- and heterodimers in vitro. 14-3-3 proteins are localised in the cytoplasm of all cells and also in the nuclei of some epithelial cells. This nuclear localisation becomes more prominent during starvation. Moreover, 14-3-3 protein is present in large amounts in food granules and from this we conclude that it performs functions which are associated with metabolism and food storage in Hydra.

GFP expression in Hydra: lessons from the particle gun

The cnidarian Hydra is an important model organism to study pattern formation and tem cell differentiation. In the past, however, it has been difficult to study gene function in Hydra because the animals have hot been accessible to gene transfection studies, we have now developed a method to transiently express GFP-tagged proteins in Hydra using a green fluorescent protein (GFP) expression plasmid under the control of the Hydra actin promoter and a particle gun to introduce it into Hydra cell nuclei. We achieve strong transient GFP expression in a small but reproducible number of epithelial and interstitial cells. Implications for the use of this method to carry out single cell assays with GFP-tagged Hydra proteins are discussed.

An immunoelectron study of karyosphere and nuclear bodies in oocytes of mealworm beetle, Tenebrio molitor (Coleoptera: polyphaga)

The karyosphere and nuclear bodies (NBs) were studied in Tenebrio molitor oocytes using immunoelectron cytochemistry. During early diplotene (previtellogenic stage), oocyte chromosomes begin to unite in a small nuclear volume forming the karyosphere. In vitellogenic oocyte nuclei, the chromatin undergoes condensation, and the karyosphere acquires a ring-shaped structure. The karyosphere is the only structure containing DNA in the oocyte nucleus. Pre-mRNA splicing factors [small nuclear ribonucleoproteins (snRNPs) and SC35] are not found in the karyosphere itself. In previtellogenic oocyte nuclei, these factors are present in NBs and in a fibrogranular substance surrounding the chromosomes in the early stages of karyosphere formation. At this stage, larger fibrillar NBs contain the non-snRNP splicing factor SC35. Smaller roundish NBs were shown to contain snRNPs. Some NBs with the same morphology contain neither snRNPs nor SC35. In the vitellogenic oocyte, there are fibrogranular NBs containing both snRNPs and SC35 splicing factors, fibrillar NBs containing snRNPs only, and complex NBs containing both. Complex NBs are often connected with the ring-shaped karyosphere. Based on the obtained immunoelectron data, we suggest that T. molitor oocyte NBs containing both snRNPs and the non-snRNP splicing factor SC35 are homologs of the well-characterized B-snurposomes in amphibian germinal vesicles and clusters of interchromatin granules in mammalian oocyte nuclei. Other NBs containing only snRNPs are suggested to represent a special class of insect oocyte snurposomes. The nuclear organelles mentioned seem to play a role as storage domains for pre-mRNA splicing factors during T. molitor oogenesis.