The developmental biology of neural connectivity.
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How can the development of an ordered array of neuronal connections be encoded in the genome? Results on the establishment of sensory connections in insects indicate that this programming is a multi-stepped process which begins as soon as the first axons develop. Because each step relies on the previous level of organization, the first steps of the process are subject to intense structural constraints, and therefore have been largely conserved through evolution. What is known of the molecular biology of some essential steps, like the differentiation of excitable cells, their aggregation in nerve cords, and the diversification of a periodic structure, supports the idea that the basic organization of the CNS evolved before the divergence between the chordate and the arthropod/annelid lineage. (+info)
Atypical phenotypes from flatworm Kv3 channels.
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Divergence of the Shaker superfamily of voltage-gated (Kv) ion channels early in metazoan evolution created numerous electrical phenotypes that were presumably selected to produce a wide range of excitability characteristics in neurons, myocytes, and other cells. A comparative approach that emphasizes this early radiation provides a comprehensive sampling of sequence space that is necessary to develop generally applicable models of the structure-function relationship in the Kv potassium channel family. We have cloned and characterized two Shaw-type potassium channels from a flatworm (Notoplana atomata) that is arguably a representative of early diverging bilaterians. When expressed in Xenopus oocytes, one of these cloned channels, N.at-Kv3.1, exhibits a noninactivating, outward current with slow opening kinetics that are dependent on both the holding potential and the activating potential. A second Shaw-type channel, N.at-Kv3.2, has very different properties, showing weak inward rectification. These results demonstrate that broad phylogenetic sampling of proteins of a single family will reveal unexpected properties that lead to new interpretations of structure-function relationships. (+info)
Ecological functions of tetrodotoxin in a deadly polyclad flatworm.
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The deadly neurotoxin tetrodotoxin (TTX) is found in a variety of animal phyla and, because of its toxicity, is most often assumed to deter predation. On the tropical Pacific island of Guam, we found an undescribed flatworm (planocerid sp. 1) that contains high levels of TTX and its analogs. Through ecological experiments, we show that TTXs do not protect these flatworms from some predators but instead are used to capture mobile prey. TTX is known to have multiple ecological functions, which has probably led to its widespread presence among prokaryotes and at least 10 metazoan phyla. (+info)
Activating effect of light irradiation at various wavelength on the respiration in sperm of the echiuroid, Urechis unicinctus, in the presence of carbon monoxide.
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In sperm of the echiuroid, Urechis unicinctus, respiration in the presence of CO was reversibly augmented by light irradiation in an examined range of wavelengths between 350 and 650 nm. The respiratory rate of sperm in the presence of CO was enhanced by light irradiation in proportion to the light fluence rate. A sharp and large peak was obtained at the wavelength of 430 nm in the action spectrum of photo-activated respiration of sperm in the presence of CO. Broad and small peaks were also found at around 530 and 570 nm. This action spectrum is similar in its profile to the absorption spectrum of reduced cytochrome b. Absorption of photon energy by reduced b-type cytochrome probably activates the redox reaction of this cytochrome to enhance the respiratory rate. Photo-activated respiration in the presence of CO was inhibited by antimycin A and cyanide. In this respiratory system, an electron equivalent is probably transferred through the mitochondrial respiratory chain between cytochrome b and cytochrome c and finally to molecular oxygen in the reaction catalyzed by the CO-insensitive terminal oxidase. (+info)
Voltage-gated calcium channel subunits from platyhelminths: potential role in praziquantel action.
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Voltage-gated calcium (Ca2+) channels provide the pathway for Ca2+ influxes that underlie Ca2+ -dependent responses in muscles, nerves and other excitable cells. They are also targets of a wide variety of drugs and toxins. Ca2+ channels are multisubunit protein complexes consisting of a pore-forming alpha(1) subunit and other modulatory subunits, including the beta subunit. Here, we review the structure and function of schistosome Ca2+ channel subunits, with particular emphasis on variant Ca2+ channel beta subunits (Ca(v)betavar) found in these parasites. In particular, we examine the role these beta subunits may play in the action of praziquantel, the current drug of choice against schistosomiasis. We also present evidence that Ca(v)betavar homologs are found in other praziquantel-sensitive platyhelminths such as the pork tapeworm, Taenia solium, and that these variant beta subunits may thus represent a platyhelminth-specific gene family. (+info)
The regeneration capacity of the flatworm Macrostomum lignano--on repeated regeneration, rejuvenation, and the minimal size needed for regeneration.
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The lion's share of studies on regeneration in Plathelminthes (flatworms) has been so far carried out on a derived taxon of rhabditophorans, the freshwater planarians (Tricladida), and has shown this group's outstanding regeneration capabilities in detail. Sharing a likely totipotent stem cell system, many other flatworm taxa are capable of regeneration as well. In this paper, we present the regeneration capacity of Macrostomum lignano, a representative of the Macrostomorpha, the basal-most taxon of rhabditophoran flatworms and one of the most basal extant bilaterian protostomes. Amputated or incised transversally, obliquely, and longitudinally at various cutting levels, M. lignano is able to regenerate the anterior-most body part (the rostrum) and any part posterior of the pharynx, but cannot regenerate a head. Repeated regeneration was observed for 29 successive amputations over a period of almost 12 months. Besides adults, also first-day hatchlings and older juveniles were shown to regenerate after transversal cutting. The minimum number of cells required for regeneration in adults (with a total of 25,000 cells) is 4,000, including 160 neoblasts. In hatchlings only 1,500 cells, including 50 neoblasts, are needed for regeneration. The life span of untreated M. lignano was determined to be about 10 months. (+info)
Phosphatized polar lobe-forming embryos from the Precambrian of southwest China.
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In developing embryos of some extant spiralian animals, polar lobe formation is one of the symmetry-breaking mechanisms for segregation of maternal cytoplasmic substances to certain blastomeres and not others. Polar lobe formation leads to unique early cleavage morphologies that include trilobed, J-shaped, and five-lobed structures. Fossil embryos similar to modern lobeforming embryos are recognized from the Precambrian Doushantuo Formation phosphates, Weng'an, Guizhou Province, China. These embryos are abundant and form a developmental sequence comparable to different developing stages observed in lobe-forming embryos of extant spiralians. These data imply that lobe formation is an evolutionarily ancient process of embryonic specification. (+info)
Hepatic Calyptospora sp. (Apicomplexa) infection in a wild-born, aquarium-held clutch of juvenile arapaima Arapaima gigas (Osteoglossidae).
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From Manaus, Brazil, 12 juvenile arapaima Arapaima gigas were imported to the United States and sent to 2 public aquaria, 1 private hobbyist, and 1 retailer. All 12 fish became ill within 4 to 6 wk of arrival, with signs of anorexia, lethargy, depigmentation, and ascites, and subsequently died despite antibiotic and anthelminthic therapy. Gross necropsies of 7 fish revealed serosanguinous coelomic effusion in all 7 fish, and branchial monogeneosis in 3 of 6 fish. The monogeneans from 1 fish were identified as Dawestrema cycloancistrium (Ancyrocephalinae). Histologic examination of 7 fish showed a variety of lesions, principally in the liver, gills, brain and gastro-intestinal tract. Numerous coccidian oocysts replaced 15 to 33% of the liver parenchyma in 6 of 7 fish examined. Light and transmission electron microscopy revealed that each oocyst contained 4 pyriform sporocysts bearing numerous sporopodia on their tapering, posterior end; approximately 25 to 30% of the length of the sporocyst was adorned. Each sporocyst was covered by a thin, membranous veil, contained 2 sporozoites, and stained brilliant pink with the Ziehl-Neelsen acid-fast method. This morphology is consistent with that of Calyptospora sp. (Lack of fresh material precluded determination to species.) This is the first report of Calyptospora sp. in arapaima. The Calyptospora sp. infection probably contributed to the morbidity and mortality of the captive arapaima. (+info)