Temporal distribution and population structure of two congeneric species of Cucullanus (Nematoda: Cucullanidae) in Orthopristis ruber in Venezuela.

The qualitative and quantitative parameters of temporal distribution of Cucullanus tripapillatus and Cucullanus chrysophrydes in the intestine of Orthopristis ruber in the Caribbean Sea on the north of Margarita Island, Venezuela were analysed. A total of 540 fish were collected at random from the catch of commercial trawlers during 1982-83 and 1992-93. Both species of Cucullanus were found throughout the year; prevalence and mean intensity of C. tripapillatus were higher than that of C. chrysophrydes. A significant difference was found in infection between the two years of sampling. Female worms were more abundant than male in both years. Both species exhibited pronounced prevalence and maturity in September and March of each year, indicating seasonality. The patterns of occurrence of the two species of Cucullanus in O. ruber did not change in the 10-year interval but the host size and number of parasites declined, which may be due to over-exploitation of definitive fish hosts.

Population and seasonal distribution of Procamallanus daccai in Eutropiichthys vacha in Kaptai Lake, Chittagong, Bangladesh.

The population and seasonal distribution of Procamallanus daccai (Nematoda: Procamallanidae) in Eutropiichthys vacha (Siluridae) from the Kaptai Lake were studied for a period of 20 months during 1986-1987. A total of 208 fish were necropsied and 5652 worms were recovered, of which 2392 were from 87 infected male fish and 3260 were from 89 infected female fish. Prevalence values varied from 50% to 95%. The intensity and abundance of nematodes fluctuated over the study period and are statistically significant (F=14.87, P<0.0001), and showed a seasonal preference for the summer period (F=33.39, P<0.05). The mean intensity was the highest in the smallest size group at 66.3+/-12.7 which gradually decreased to 4+/-1.89 in the largest size group. No significant differences were found between parasites from male and female hosts, except in the summer. Male parasites were less abundant in the population. Female worms were grouped into immature, maturing and gravid and all these stages were present throughout the year. The highest occurrence of both immature and gravid P. daccai was found during the months of February to April each year. Peak recruitment seems to occur during this period due to the presence of high quantities of immature worms.

A new species of Microphallus (Trematoda: Microphallidae) from Venezuela

During 1997-1999, a total of 94 crabs, Uca rapax were collected from La Sabana, La Ceiba and El Paujil, Sucre State, Venezuela. Of these 36 were infected with metacercariae. Two parasites were located in the abdominal muscles and one under the tissue of carapace and gonad. These metacercariae grew to adults in the following genera: Levinseniella, Microphallus and Maritrema, in the period of 2-5 days after feeding experimentally to the rat Rattus norvegicus, mice Mus musculus and duck Cairinia moschata. Specimens of the genus Microphallus were described herein as a new species M. sabanensis. The life cycle of M. sabanensis sp.nov. were studied experimentally using rat, mice and duck. All developmental stages and the adult are described. In addition, M. sabanensis was collected from wild birds Anas discors, Pluvialis squatarola, Butorides striatus, Egretta caerulea and Nycticorax violaceus from the same localities.

A new species of Microphallus (Trematoda: Microphallidae) from Venezuela.

During 1997-1999, a total of 94 crabs, Uca rapax were collected from La Sabana, La Ceiba and El Paujil, Sucre State, Venezuela. Of these 36 were infected with metacercariae. Two parasites were located in the abdominal muscles and one under the tissue of carapace and gonad. These metacercariae grew to adults in the following genera: Levinseniella, Microphallus and Maritrema, in the period of 2-5 days after feeding experimentally to the rat Rattus norvegicus, mice Mus musculus and duck Cairinia moschata. Specimens of the genus Microphallus were described herein as a new species M. sabanensis. The life cycle of M. sabanensis sp.nov. were studied experimentally using rat, mice and duck. All developmental stages and the adult are described. In addition, M. sabanensis was collected from wild birds Anas discors, Pluvialis squatarola, Butorides striatus, Egretta caerulea and Nycticorax violaceus from the same localities.

[Some attributes of community structure of fishes in Laguna Grande de Obispo, Golfo Cariaco, Sucre State, Venezuela]. / Algunos atributos de la estructura comunitaria de la ictiofauna de la Laguna Grande de Obispo, Golfo de Cariaco, Venezuela.

Species composition, relative abundance, diversity and community structure of fishes were studied from monthly sampling during December 1995 to November 1996 in the Laguna Grande de Obispo, Gulf of Cariaco, Sucre State, Venezuela. Sampling were realised in 3 stations inside the lagoon with a small beach seine and the other 4 stations with a large beach seine. Seventy four species belonging to 33 families and 68 genera were identified of which 8 species dominated, constituting 90.43% of total catch. Mugil curema, Xenomelaniris brasiliensis, Opistonema oglinum, Atherinomorus stipes and Anchoa hepsetus were present in high abundance in the biomass. M. curema dominated the catch with large seine while X. brasiliensis, M. curema and Eucinostomus argenteus dominated the catch with small seine. Species diversity (H') ranged from 2.968-4.607 bits/ind and species richness of Margalef from 2.752-7.464. An inverse analysis realized on catches by small seine and based on nodal constancy and fidelity allowed to define a pattern of spatial distribution of 9 groups containing 1 to 11 species on the basis their abundance, frequency of appearance and ecological characteristics of each area. An analysis of correlation showed that the salinity, dissolved O2 and precipitation did not show any significant correlation with the ecological parameters studied but existed significant correlation with average surface water temperature (p < 0.05), number of species (S), individuals (N), diversity (H') and species richness (D). The positive correlation was found with surface temperature but no relationship with relative dominance (D1 and D2). The CPUE in biomass did not show any significant association with temperature.

Spatial and temporal control of RNA stability.

Maternally encoded RNAs and proteins program the early development of all animals. A subset of the maternal transcripts is eliminated from the embryo before the midblastula transition. In certain cases, transcripts are protected from degradation in a subregion of the embryonic cytoplasm, thus resulting in transcript localization. Maternal factors are sufficient for both the degradation and protection components of transcript localization. Cis-acting elements in the RNAs convert transcripts progressively (i) from inherently stable to unstable and (ii) from uniformly degraded to locally protected. Similar mechanisms are likely to act later in development to restrict certain classes of transcripts to particular cell types within somatic cell lineages. Functions of transcript degradation and protection are discussed.

[Spatial and temporal variation of the fish community inhabiting the Laguna Grande de Obispo, Gulf of Cariaco, Sucre State, Venezuela]. / Variacion espacio-temporal de la comunidad de peces en Laguna Grande de Obispo, Golfo de Caroaco, Estado Sucre, Venezuela.

The monthly species composition and the spatial and temporal variation of fish community of Laguna Grande de Obispo, Gulf of Canaco, Sucre State, Venezuela were analyzed. The samples were collected using two beach seines of different size from December 1995 to November 1996. A cluster analysis for stations inside the lagoon and time of capture showed 4 major groups, defined principally with ecological parameters of each area. Fishing with large seine in and outside the lagoon showed two large groups which were divided into 10 subgroups in function of station and time, while an inverse analysis of the same sample differentiated into 8 groups of species. based on distribution, dominance, and occurrence. Xenomeianiris brasiliensis, Mugil curema and Eucinostomus argenteus were the most abundant species in both time and space. An analysis of conglomerate on the whole fish community of the sampling period indicated the existence of two groups: i) the first half of the year including December 1995 and October 1996 and ii) the second half of the year. The distribution of fishes in relation to ecological factors is discussed.

Distinct human NUMB isoforms regulate differentiation vs. proliferation in the neuronal lineage.

Neuronal cell fate decisions are directed in Drosophila by NUMB, a signaling adapter protein with two protein-protein interaction domains: a phosphotyrosine-binding domain and a proline-rich region (PRR) that functions as an SH3-binding domain. Here we show that there are at least four human NUMB isoforms and that these serve two distinct developmental functions in the neuronal lineage: differentiation (but not proliferation) is promoted by human NUMB protein isoforms with a type I (short) PRR. In contrast, proliferation (but not differentiation) is directed by isoforms that have a type II (long) PRR. The two types of PRR may promote distinct intracellular signaling pathways downstream of the NOTCH receptor during mammalian neurogenesis.

Joint action of two RNA degradation pathways controls the timing of maternal transcript elimination at the midblastula transition in Drosophila melanogaster.

Maternally synthesized RNAs program early embryonic development in many animals. These RNAs are degraded rapidly by the midblastula transition (MBT), allowing genetic control of development to pass to zygotically synthesized transcripts. Here we show that in the early embryo of Drosophila melanogaster, there are two independent RNA degradation pathways, either of which is sufficient for transcript elimination. However, only the concerted action of both pathways leads to elimination of transcripts with the correct timing, at the MBT. The first pathway is maternally encoded, is targeted to specific classes of mRNAs through cis-acting elements in the 3'-untranslated region and is conserved in Xenopus laevis. The second pathway is activated 2 h after fertilization and functions together with the maternal pathway to ensure that transcripts are degraded by the MBT.

RNA localization in development.

Cytoplasmic RNA localization is an evolutionarily ancient mechanism for producing cellular asymmetries. This review considers RNA localization in the context of animal development. Both mRNAs and non-protein-coding RNAs are localized in Drosophila, Xenopus, ascidian, zebrafish, and echinoderm oocytes and embryos, as well as in a variety of developing and differentiated polarized cells from yeast to mammals. Mechanisms used to transport and anchor RNAs in the cytoplasm include vectorial transport out of the nucleus, directed cytoplasmic transport in association with the cytoskeleton, and local entrapment at particular cytoplasmic sites. The majority of localized RNAs are targeted to particular cytoplasmic regions by cis-acting RNA elements; in mRNAs these are almost always in the 3'-untranslated region (UTR). A variety of trans-acting factors--many of them RNA-binding proteins--function in localization. Developmental functions of RNA localization have been defined in Xenopus, Drosophila, and Saccharomyces cerevisiae. In Drosophila, localized RNAs program the antero-posterior and dorso-ventral axes of the oocyte and embryo. In Xenopus, localized RNAs may function in mesoderm induction as well as in dorso-ventral axis specification. Localized RNAs also program asymmetric cell fates during Drosophila neurogenesis and yeast budding.

Fringe boundaries coincide with Notch-dependent patterning centres in mammals and alter Notch-dependent development in Drosophila.

In both vertebrate and invertebrate development, cells are often programmed to adopt fates distinct from their neighbors. Genetic analyses in Drosophila melanogaster have highlighted the importance of cell surface and secreted proteins in these cell fate decisions. Homologues of these proteins have been identified and shown to play similar roles in vertebrate development. Fringe, a novel signalling protein, has been shown to induce wing margin formation in Drosophila. Fringe shares significant sequence homology and predicted secondary structure similarity with bacterial glycosyltransferases. Thus fringe may control wing development by altering glycosylation of cell surface and/or secreted molecules. Recently, two fringe genes were isolated from Xenopus laevis. We report here the cloning and characterization of three murine fringe genes (lunatic fringe, manic fringe and radical fringe). We find in several tissues that fringe expression boundaries coincide with Notch-dependent patterning centres and with Notch-ligand expression boundaries. Ectopic expression of murine manic fringe or radical fringe in Drosophila results in phenotypes that resemble those seen in Notch mutants.

Mammalian NUMB is an evolutionarily conserved signaling adapter protein that specifies cell fate.

BACKGROUND: Drosophila numb was originally described as a mutation affecting binary divisions in the sensory organ precursor (SOP) lineage. The numb gene was subsequently shown to encode an asymmetrically localized protein which is required for binary cell-fate decisions during peripheral nervous system development. Part of the Drosophila NUMB protein exhibits homology to the SHC phosphotyrosine-binding (PTB) domain, suggesting a potential link to tyrosine-kinase signal transduction. RESULTS: A widely expressed mammalian homologue of Drosophila numb (dnumb) has been cloned from rat and is referred to here as mammalian Numb (mNumb). The mNUMB protein has a similar overall structure to dNUMB and 67 sequence similarity. Misexpression of mNumb in Drosophila during sensory nervous system precursor cell division causes identical cell fate transformations to those produced by ectopic dNUMB expression. In vitro, the mNUMB PTB domain binds phosphotyrosine-containing proteins, and SH3 domains of SRC-family tyrosine kinases bind to mNUMB presumably through interactions with proline-rich regions in the carboxyl terminus. Overexpression of full-length mNUMB in the multipotential neural crest stem cell line MONC-1 dramatically biases its differentiation towards neurons, whereas overexpression of the mNUMB PTB domain biases its differentiation away from neuronal fates. CONCLUSIONS: Our results demonstrate that mNUMB is an evolutionarily conserved functional homologue of dNUMB, and establish a link to tyrosine-kinase-mediated signal transduction pathways. Furthermore, our results suggest that mNUMB and dNUMB are new members of a family of signaling adapter molecules that mediate conserved cell-fate decisions during development.