From tumors to species: a SCANDAL hypothesis.

ᅟ: Some tumor cells can evolve into transmissible parasites. Notable examples include the Tasmanian devil facial tumor disease, the canine transmissible venereal tumor and transmissible cancers of mollusks. We present a hypothesis that such transmissible tumors existed in the past and that some modern animal taxa are descendants of these tumors. We expect potential candidates for SCANDALs (speciated by cancer development animals) to be simplified relatives of more complex metazoans and have genomic alterations typical for cancer progression (such as deletions of universal apoptosis genes). We considered several taxa of simplified animals for our hypothesis: dicyemida, orthonectida, myxosporea and trichoplax. Based on genomic analysis we conclude that Myxosporea appear to be the most suitable candidates for a tumor ancestry. They are simplified parasitic cnidarians that universally lack major genes implicated in cancer progression including all genes with Caspase and BCL2 domains as well as any p53 and apoptotic protease activating factor - 1 (Apaf-1) homologs, suggesting the disruption of main apoptotic pathways in their early evolutionary history. Further comparative genomics and single-cell transcriptomic studies may be helpful to test our hypothesis of speciation via a cancerous stage. REVIEWERS: This article was reviewed by Eugene Koonin, Mikhail Gelfand and Gregory M Woods.

Sleep-wakefulness cycle and behavior in pannexin1 knockout mice.

Pannexins are membrane channel proteins that play a role in a number of critical biological processes (Panchin et al., 2000; Shestopalov, Panchin, 2008). Among other cellular functions, pannexin hemichannels serve as purine nucleoside conduits providing ATP efflux into the extracellular space (Dahl, 2015), where it is rapidly degraded to adenosine. Pannexin1 (Panx1) is abundantly expressed in the brain and has been shown to contribute to adenosine signaling in nervous system tissues (Prochnow et al., 2012). We hypothesized that pannexin1 may contribute to sleep-wake cycle regulation through extracellular adenosine, a well-established paracrine factor in slow wave sleep. To investigate this link, EEG and movement activity throughout the light/dark cycle were compared in Panx1-/- and Panx1+/+ mice. We found a significant increase in waking and a correspondent decrease in slow wave sleep percentages in the Panx1-/- animals. These changes were especially pronounced during the dark period. Furthermore, we found a significant increase in movement activity of Panx1-/- mice. These findings are consistent with the hypothesis that extracellular adenosine is relatively depleted in Panx1-/- animals due to the absence of the ATP-permeable hemichannels. At the same time, sleep rebound after a 6-h sleep deprivation remained unchanged in Panx1-/- mice as compared to the control animals. Behavioral tests revealed that Panx1-/- mice were significantly faster during their descent along the vertical pole but more sluggish during their run through the horizontal pole as compared to the control mice.

In search of the origin of FREPs: characterization of Aplysia californica fibrinogen-related proteins.

All haemolymph lectins with uniquely juxtaposed N-terminal domain similar to the immunoglobulin superfamily (IgSF) and C-terminal fibrinogen (FBG) termed FBG-related proteins (FREP) are documented till now only in the pulmonate mollusc Biomphalaria glabrata. Using genomic WGS database we have found two FREP genes from marine opistobranch Aplysia californica named AcFREP1 and AcFREP2. The AcFREP1 and AcFREP2 mRNA molecules have been subsequently isolated from cDNA of sea hare larvae as well as adult mollusc tissues. These genes encode proteins (504 and 510aa respectively) with domain architecture typical for FREPs with two N-terminal IgSF domains and C-terminal FBG domain. Although cDNA sequences of AcFREP1 and AcFREP2 are 81% identical, their genomic structure is entirely different: AcFREP1 is intronless and AcFREP2 is encoded in four exons. These genes are paralogous pair in which AcFREP2 is a parental gene and AcFREP1 is the new transposed copy that has lost the introns (retrogene). Using RT-PCR analysis, expression of AcFREP1 and AcFREP2 was shown to be developmentally and tissue-specific and no constitutive expression in haemocytes was found. The overall frequency of nucleotide substitutions in genomic DNA trace sequences of coding region of the AcFREP1 and AcFREP2 is not higher than in the sequences of control conserved genes (actin, FMRFamide). Thus, previously reported high diversification of Biomphalaria FREP gene, BgFREP3, is not detected in Aplysia FREPs. A search for FREP homologs in other available complete genome of mollusc, Lottia gigantea (Patellogastropoda), a representative of the evolutionary earliest gastropod clade, did not reveal any DNA sequences coding for similar lectins. We suggest that unique domain architecture of FREPs is an evolutionary novelty that appeared and evolved only within one branch of Protostomata species, exclusively in heterobranch molluscs (Pulmonata and Opistobranchia).

A new human gene KCNRG encoding potassium channel regulating protein is a cancer suppressor gene candidate located in 13q14.3.

We report the primary characterization of a new gene KCNRG mapped at chromosome band 13q14.3. This gene includes three exons and has two alternatively spliced isoforms that are expressed in normal tissues and in some tumor cell lines. Protein KCNRG has high homology to tetramerization domain of voltage-gated K+ channels. Using the patch-clamp technique we determined that KCNRG suppresses K+ channel activity in human prostate cell line LNCaP. It is known that selective blockers of K+ channels suppress lymphocyte and LNCaP cell line proliferation. We suggest that KCNRG is a candidate for a B-cell chronic lymphocytic leukemia and prostate cancer tumor suppressor gene.

Hydrobia ulvae (Gastropoda: Prosobranchia): a new model for regeneration studies.

Within 2 weeks of decapitation, Hydrobia ulvae was able to regenerate new head structures including buccal ganglia. It was also capable of regenerating propodial ganglia after anterior foot amputation. The functional regeneration of the buccal ganglia was demonstrated by behavioural observations and by electrophysiological experiments. The presence of the oesophagus was shown to be important for regeneration of the buccal complex. H. ulvae provides a new model for regeneration studies, so details of the topographic anatomy and biology of this species are described. To standardize experimental animals in future studies, the effects of age, sex and trematode infestation on the regeneration capacity of H. ulvae have been evaluated. The high capacity for regeneration together with the possibility of using electrophysiological techniques makes H. ulvae a favourable model in which to study neurogenesis in adult animals.

The role of putative glutamatergic neurons and their connections in the locomotor central pattern generator of the mollusk, Clione limacina.

In the pteropod mollusk Clione limacina, locomotor rhythm is produced by the central pattern generator (CPG), due mainly to the activity of interneurons of groups 7 (active in the phase of the dorsal flexion of the wings) and 8 (active in the phase of the ventral flexion). Each of these groups excites the neurons active in the same phase of the locomotor cycle, and inhibits the neurons of the opposite phase. In this work, the nature of connections formed by group 7 interneurons was studied. Riluzole (2-amino-6-trifluoro-methoxybenzothiazole), which is known to inhibit the presynaptic release of glutamate, suppressed the action of the type 7 interneurons onto the follower neurons of the same and of the antagonistic phase of the locomotor cycle. The main pattern of rhythmic activity of CPG with alternation of two phases could be maintained after suppression of inhibitory connections from group 7 interneurons to antagonistic neurons. This suggests redundancy of the mechanisms controlling swimming rhythm generation, which ensures the reliable operation of the system.

Projection pattern and target selection of Clione limacina motoneurons sprouting within an intact environment.

In the pteropod mollusc Clione limacina, two groups of locomotor motoneurons, located in the pedal ganglion, innervate the dorsal and ventral muscle layers of the ipsilateral wing through the wing nerve. Separate branches of this nerve go either only to the dorsal muscle layer or only to the ventral one. In the present study, growth of novel neurites of the wing motoneurons was induced by cutting the wing nerve. In addition, all other peripheral nerves and connectives of the pedal ganglion were cut, except for the pedal commissure to the contralateral pedal ganglion. Thus, the neurites were allowed to grow only towards the contralateral pedal ganglion. We have found that the novel neurites, entering the contralateral pedal ganglion, were capable of growing everywhere inside the central nervous system (CNS) and into any peripheral nerve. However, they preferred the wing nerve. This finding suggests that the preference is caused by the guiding cues in the wing nerve or the attractive influence of the wing muscles. Because the contralateral pedal ganglion and nerves were left intact, the growth direction of the new neurites could be determined only by factors permanently existing in the CNS, rather than induced by nerve injury or muscle denervation. Within the wing nerve, the neurites could not discriminate between the nerve branches going to the dorsal and ventral muscle layers. They formed synapses on muscles of both layers, despite the fact that the muscles were innervated by their own motoneurons.

Short-circuited neuron: a note.

Here, we demonstrate in a direct electrophysiological experiment that a neuron can form electrical connections to itself. An isolated identified neuron with a long axon was plated in culture and the axon was looped so that its distal end contacted the cell body. After two days in culture, the cell body and the axon were both impaled with microelectrodes and the axon segment between the recording electrodes was cut. Electrotonic coupling was revealed between the separated cell compartments immediately after axon transection. In contrast to an earlier publication [Guthrie P. B. et al. (1994) J. Neurosci. 14, 1477-1485], no constraints on the formation of the electrical connections between different parts of the same neuron were revealed in our experiments.Thus, these experiments demonstrate that in vitro culture of a single neuron can form reflexive electrical connections which may strongly affect the basic properties of the neuron and should be taken into account in both experimental and model electrophysiological studies.

Axotomized neurons of the pteropod mollusc Clione limacina develop novel sites of transmitter release in the absence of their normal muscle target.

Neural network for rhythmic wing movements in the swimming mollusc Clione limacina is a well-studied system. After nerve transection the efferent wing neurons cannot reach muscles and consequently display intensive central sprouting. In the present work it was shown that two types of efferent neurons with different neurotransmitters: acethylcholinergic locomotor motoneurons and serotonergic modulatory efferent neurons when deprived of their normal targets, release their neurotransmitter intended for peripheral muscles, in the unusual compartment--neuropile. Such 'unauthorized' release of neurotransmitter may cause nervous system dysfunctions in the damaged brain of other animals.

Selective regeneration of the neuromuscular connections in the pteropod mollusc Clione limacina.

In the pteropod mollusc Clione limacina, two different groups of motoneurons innervate two physiologically identical wing muscles (dorsal and ventral). When motoneuron axons are crushed in the nerve of whole animals regeneration starts. In its course motoneurons initially project to both the correct and incorrect muscles. Then incorrect connections and neurites are eliminated and the original innervation is restored. Here we investigated neuromuscular regeneration when one of the muscles was removed or the muscle size was reduced. Motoneurons formed both correct and incorrect connections not only in vitro when the pedal ganglion was attached to only one of two wing muscles, but also in whole-animal 'no choice' experiments when only one muscle was available for reinnervation. In these experiments incorrect connections were stable and were not eliminated at the later stages, as happened in experiments in which both muscles were accessible. In whole-animal experiments with reduced size of the muscles, a normal pattern of regeneration was conserved although not all incorrect connections were eliminated. Thus, in the course of regeneration: (i) locomotor motoneurons make connections with both correct and incorrect muscles; (ii) if for some group of motoneurons the correct targets are unavailable, the incorrect connections survive and become stable; (iii) if both groups of motoneurons have a choice between the correct and incorrect targets, initial mixed innervation is replaced by purely correct innervation; (iv) elimination of incorrect synapses could be a result of the competition between correct and incorrect synapses of the same neuron.

Analysis of the central pattern generator for swimming in the mollusk Clione.

The pteropod mollusk Clione limacina swims by rhythmic movements of two wings. The central pattern generator (CPG) for swimming, located in the pedal ganglia, is formed by three groups of interneurons. The interneurons of the groups 7 and 8 are of crucial importance for rhythm generation. They are endogenous oscillators capable of generating rhythmic activity with a range of frequencies typical of swimming after extraction from the ganglia. This endogenous rhythmic activity is enhanced by serotonin. The interneurons 7 and 8 produce one prolonged action potential (about 100 ms in duration) per cycle. Prolonged action potentials contribute to determining the duration of the cycle phases. The interneurons of two groups inhibit one another determining their reciprocal activity. The putative transmitters of groups 7 and 8 interneurons are glutamate and acetylcholine, respectively. Transition from one phase to the other is facilitated by the plateau interneurons of group 12 that contribute to termination of one phase and to initiation of the next phase. Maintaining the rhythm generation and transition from one phase to the other is also promoted by postinhibitory rebound. The redundant organization of the swimming generator guarantees the high reliability of its operation. Generation of the swimming output persisted after the inhibitory input from interneurons 8 to 7 had been blocked by atropine. Activity of the swimming generator is controlled by a set of command neurons that activate, inhibit or modulate the operation of the swimming CPG in relation to a behaviorally relevant context.

Cell lineage in marine nematode Enoplus brevis.

Early cleavages of the marine nematode Enoplus brevis are symmetrical and occur in synchrony. At the 2- to 16-cell stages, blastomeres are indistinguishable. The progeny of blastomeres was investigated by intracellular injections of fluorescent dyes and horse radish peroxidase. One blastomere of the 2-cell embryo gives rise to a compact group of cells occupying about half of an embryo. The border between labeled and unlabeled cells differs in each embryo dividing it to anterior-posterior, left-right or intermediate parts. At the 8-cell stage, one blastomere gives rise to only endoderm, whereas the other blastomeres produce progeny that form multiple cell types, including nerve, muscle and hypoderm cells, in various proportions. Thus the fates of the blastomeres of early E. brevis embryos, with the exception of the endoderm precursor, are not determined. The process of gastrulation in E. brevis is very similar to that in Caenorhabditis elegans and other nematodes. At the beginning of gastrulation, the 2-celled endoderm precursor lies on the surface of embryo and then sinks inwards. After labeling of cells on the ventral side (near endoderm precursor) at the beginning of gastrulation, their progeny differentiate predominantly into body muscles or pharyngeal cells of the first stage larva. Cells that are located more laterally give rise mainly to neurons. The dorsal blastomeres differentiated principally into hypoderm cells. Our study suggests that a precise cell lineage is not a necessary attribute of nematode development.

Cellular mechanism for the temperature sensitive spatial orientation in Clione.

The swimming mollusk Clione is normally oriented vertically. As water is warmed, this orientation is lost or reversed. CPB3 interneurons, which transmit signals from the statocyst receptors (SRCs) to the tail motoneurons and play a key role in space orientation, were strongly depolarized upon warming. Normally, intracellular stimulation of the rostro-dorsal SRC (DSRC) excited CPB3b. Upon warming the excitation gradually decreased and in some cases was even replaced by inhibition. The reversal potential for the synaptic potentials (PSP) produced in CPB3b by DSRC stimulation is depolarized relative to the normal membrane potential at lower temperature. Warming causes depolarization of the membrane potential such that the PSP reversal potential is approached and even passed, with attenuant effects on PSP amplitude and polarity. This effect provides a mechanism for the temperature sensitive changes in the orientation of Clione.

Effects of acetylcholine and glutamate on isolated neurons of locomotory network of Clione.

In Clione limacina, locomotory rhythm is produced in the central pattern generator by reciprocal activity of two groups of interneurons. Dorsal (D) and ventral (V) phase interneurons activate neurons of the same phase and inhibit neurons of the opposite phase. Which neurotransmitters are used by these interneurons is not clear. In this study, identified follower neurons to V and D interneurons were isolated, and their responses to the local application of potential neurotransmitters were examined. Acetylcholine exerted inhibitory action on the isolated D-phase neurons and excitatory action on V-phase neurons. Glutamate produced excitation in D-phase neurons, and inhibition in V-phase neurons. These results suggest that acetylcholine is the neurotransmitter of D-phase interneurons, while glutamate might be the neurotransmitter of V-phase interneurons.

Control of locomotion in the marine mollusc Clione limacina. XI. Effects of serotonin.

The locomotor activity in the marine mollusc Clione limacina has been found to be strongly excited by serotonergic mechanisms. In the present study putative serotonergic cerebropedal neurons were recorded simultaneously with pedal locomotor motoneurons and interneurons. Stimulation of serotonergic neurons produced acceleration of the locomotor rhythm and strengthening of motoneuron discharges. These effects were accompanied by depolarization of motoneurons, while depolarization of the generator interneurons was considerably lower (if it occurred at all). Effects of serotonin application on isolated locomotor and non-locomotor pedal neurons were studied. Serotonin (5 x 10(-7) to 1 x 10(-6) M) affected most pedal neurons. All locomotor neurons were excited by serotonin. This suggests that serotonergic command neurons exert direct influence on locomotor neurons. Effects of serotonin on nonlocomotor neurons were diverse, most neurons being inhibited by serotonin. Some effects of serotonin on locomotor neurons could not be reproduced by neuron depolarization. This suggests that, along with depolarization, serotonin modulates voltage-sensitive membrane properties of the neurons. As a result, serotonin promotes the endogenous rhythmical activity in neurons of the C. limacina locomotor central pattern generator.

Control of locomotion in marine mollusk Clione limacina. VIII. Cerebropedal neurons.

1. The pteropod mollusk Clione limacina swims by rhythmical oscillations of two wings, and its spatial orientation during locomotion is determined by tail movements. The majority of neurons responsible for generation of the wing and tail movements are located in the pedal ganglia. On the other hand, the majority of sensory inputs that affect wing and tail movements project to the cerebral ganglia. The goal of the present study was to identify and characterize cerebropedal neurons involved in the control of the swimming central generator or motor neurons of wing and tail muscles. Cerebropedal neurons affecting locomotion-controlling mechanisms are located in the rostromedial (CPA neurons), caudomedial (CPB neurons), and central (CPC neurons) zones of the cerebral ganglia. According to their morphology and effects on pedal mechanisms, 10 groups of the cerebropedal neurons can be distinguished. 2. CPA1 neurons project through the ipsilateral cerebropedal connective to both pedal ganglia. Activation of a CPA1 by current injection resulted in speeding up of the locomotor rhythm and intensification of the firing of the locomotor motor neurons. 3. CPA2 neurons send numerous thin fibers into the ipsi- and contralateral pedal and pleural ganglia through the cerebropedal and cerebropleural connectives. They strongly inhibit the wing muscle motor neurons and, to a lesser extent, slow down the locomotor rhythm. 4. CPB1 neurons project through the contralateral cerebropedal connective to both pedal ganglia. They activate the locomotor generator. 5. CPB2 neurons also project, through the contralateral cerebropedal connective, to both pedal ganglia. They affect wing muscle motor neurons. 6. CPB3 neurons have diverse morphology: they project to the pedal ganglia either through the ipsilateral cerebropedal connective, or through the contralateral one, or through both of them. They affect putative motor neurons of the tail muscles. 7. CPC1, CPC2, and CPC3 neurons project through the ipsilateral cerebropedal connective to both pedal ganglia. They activate the locomotor generator. 8. CPC4 and CPC5 neurons project through the contralateral cerebropedal connective to the contralateral pedal ganglia. They activate the locomotor generator. 9. Serotonergic neurons were mapped in the CNS of Clione by immunohistochemical methods. Location and size of cells in two groups of serotonin-immunoreactive neurons in the cerebral ganglia appeared to be similar to those of CPA1 and CPB1 neurons. This finding suggests a possible mechanism for serotonin's ability to exert a strong excitatory action on the locomotor generator of Clione. 10. The role of different groups of cerebropedal neurons is discussed in relation to different forms of Clione's behavior in which locomotor activity is involved.

Control of locomotion in marine mollusk Clione Limacina. IX. Neuronal mechanisms of spatial orientation.

1. When swimming freely, the pteropod mollusk Clione limacina actively maintains a vertical orientation, with its head up. Any deflection from the vertical position causes a correcting motor response, i.e., bending of the tail in the opposite direction, and an additional activation of the locomotor system. Clione can stabilize not only the vertical orientation with its head up, but also the posture with its head down. The latter is observed at higher water temperature, as well as at a certain stage of hunting behavior. The postural control is absent in some forms of behavior (vertical migrations, defensive reactions, "looping" when hunting). The postural reflexes are driven by input from the statocysts. After removal of the statocysts, Clione was unable to maintain any definite spatial orientation. 2. Activity of the neuronal mechanisms controlling spatial orientation of Clione was studied in in vitro experiments, with the use of a preparation consisting of the CNS and statocysts. Natural stimulation (tilt of the preparation up to 90 degrees) was used to characterize responses in the statocyst receptor cells (SRCs). It was found that the SRCs depolarized and fired (10-20 Hz) when, during a tilt, they were in a position on the bottom part of the statocyst, under the statolith. Intracellular staining has shown that the SRC axons terminate in the medial area of the cerebral ganglia. Electrical connections have been found between some of the symmetrical SRCs of the left and right statocysts. 3. Gravistatic reflexes were studied by using both natural stimulation (tilt of the preparation) and electrical stimulation of SRCs. The reflex consisted of three components: 1) activation of the locomotor rhythm generator located in the pedal ganglia; this effect of SRCs is mediated by previously identified CPA1 and CPB1 interneurons that are located in the cerebral ganglia and send axons to the pedal ganglia; 2) bending the tail evoked by differential excitation and inhibition of different groups of tail muscle motor neurons; this effect is mediated by CPB3 interneurons; and 3) modification of wing movements by differential excitation and inhibition of different groups of wing motor neurons; this effect is mediated by CPB2 interneurons. 4. Gravistatic reflexes in the tail motor neurons were inhibited or reversed at a higher water temperature. 5. The SRCs are not "pure" gravitation sensory organs because they are subjected to strong influences from the CNS. In particular, CPC1 interneurons, participating in coordination of different aspects of the hunting behavior, exert an excitatory action on some of the SRCs, and inhibitory actions on others.(ABSTRACT TRUNCATED AT 400 WORDS)

Control of locomotion in marine mollusc Clione limacina. X. Effects of acetylcholine antagonists.

The swimming central pattern generator (CPG) of the pteropod mollusc Clione limacina is located in the pedal ganglia. It consists of three groups of interneurons (7, 8, and 12) which generate the rhythmical activity and determine the temporal pattern of the motor output, that is, phasic relations between different groups of motor neurons supplying dorsal (group 1 and 3 motor neurons) and ventral (group 2 and 4 motor neurons) muscles of the wings. In this work peripheral and central effects of acetylcholine (ACh) antagonists on the swimming control in C. limacina has been studied. The ACh antagonist atropine blocked transmission from the wing nerves to wing muscles, while gallamine triethiodide (Flaxedil), d-tubocurarine, and alpha-bungarotoxin did not affect the neuromuscular transmission. In the pedal ganglia, the ACh antagonists atropine and gallamine triethiodide blocked inhibitory postsynaptic potentials (IPSPs) produced by group 8 interneurons onto group 7 interneurons and motor neurons of groups 1 and 3. d-Tubocurarine and alpha-bungarotoxin did not affect IPSPs produced by group 8 interneurons. Although atropine and gallamine triethiodide blocked IPSPs produced by group 8 interneurons in antagonistic neurons, these drugs did not influence excitatory postsynaptic potentials (EPSPs) produced by group 8 interneurons onto group 12 interneurons. The main pattern of the swimming rhythm with an alternation of two phases of the swimming cycle persisted after elimination of inhibitory connections from group 8 interneurons to antagonistic neurons by the ACh antagonists. This suggests that there are redundant mechanisms in the system controlling C. limacina's swimming. This redundancy ensures reliable operation of the system and contributes to its flexibility.

Formation of connections between cultured identified neurones from the pleural ganglion of the pteropod mollusc Clione limacina.

A cluster of electrically interconnected neurosecretory cells (the 'white cells') involved in the control of reproductive behavior was identified in the right pleural ganglion of the marine mollusc, Clione limacina. Pleural ganglia also contain large neurons (PL1 and PL2) having no connections with each other and with the white cells. Most isolated white cells put into the simple unconditioned medium (50% L-15) adhered to the bottom of uncoated dishes and demonstrated neurite outgrowth for 7-10 days. If growing processes overlapped, the white cells formed electrical connections with each other, but they formed no connections with the PL1 and PL2 neurons. It is concluded that in the case which was under study cellular intrinsic properties were sufficient for the formation of 'correct' connections between neurones.