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At least 685 records · Page 38Linked to original sources
PubMed1995

CDC42 and Rac1 control different actin-dependent processes in the Drosophila wing disc epithelium.

Cdc42 and Rac1 are members of the rho family of small guanosinetriphosphatases and are required for a diverse set of cytoskeleton-membrane interactions in different cell types. Here we show that these two proteins contribute differently to the organization of epithelial cells in the Drosophila wing imaginal disc. Drac1 is required to assemble actin at adherens junctions. Failure of adherens junction actin assembly in Drac1 dominant-negative mutants is associated with increased cell death. Dcdc42, on the other hand, is required for processes that involve polarized cell shape changes during both pupal and larval development. In the third larval instar, Dcdc42 is required for apico-basal epithelial elongation. Whereas normal wing disc epithelial cells increase in height more than twofold during the third instar, cells that express a dominant-negative version of Dcdc42 remain short and are abnormally shaped. Dcdc42 localizes to both apical and basal regions of the cell during these events, and mediates elongation, at least in part, by effecting a reorganization of the basal actin cytoskeleton. These observations suggest that a common cdc42-based mechanism may govern polarized cell shape changes in a wide variety of cell types.

Actins↗
PubMed1997

six-banded, a novel Drosophila gene, is expressed in 6 segmental stripes during embryonic development and in the eye imaginal disc.

We have characterised a Drosophila P-element enhancer detector insertion F125, which is expressed in the embryonic head and CNS as well as in various third instar imaginal discs. In an attempt to identify the gene with the equivalent expression pattern, we have characterised an adjacent gene. It encodes two novel conceptual proteins: Type I (1182 amino acids) and Type II, representing a shorter form of 774 amino acids truncated at both termini relative to Type I that is generated by alternative splicing. Based on its embryonic expression pattern, the gene was called six-banded (sba). Both splice forms are expressed in a unique embryonic pattern: initially as 6, then 12 stripes during early stages of embryonic development. Subsequently, expression is found in the developing trachae and during larval development is restricted to the eye imaginal disc where both transcripts are present immediately anterior to and behind the morphogenetic furrow. While sba expression in the eye antennal disc is mirrored by the expression of the adjacent F125 P-element, other patterns reported by this enhancer detector are not mimicked by the sba gene suggesting that the expression of the P-element represents a 'composite' of the effects of nearby enhancers.

Animals↗
PubMed1998

Impact of low water temperature on the development of Anguillicola crassus in the final host Anguilla anguilla.

The effect of low water temperatures on the development and viability of larval and adult Anguillicola crassus (Nematoda) in the final host Anguilla anguilla was studied. European eels were experimentally infected with A. crassus and then maintained for 4 mo at 4, 9, 10, and 19 degrees C. Larval development showed a temperature-dependent pattern and was significantly retarded at low temperatures. Third-stage larvae survived a 4 mo period at 4 degrees C without being affected, although they were not able to invade the swimbladder wall at this temperature. In contrast, adult worms were severely harmed during a 4 mo period at 4 degrees C, as reflected by increased mortality and decreased growth and reproductivity as compared to the worms maintained for the same period at 18 degrees C. Starvation for the eels at 4 mo at 19 degrees C did not affect the development and growth of the nematode. The experimentally obtained results support the hypothesis that the spread of A. crassus in boreal regions, e.g. Northern Europe, is restricted by the natural ambient temperature regimes.

Air Sacs↗
PubMed1981

The development of Parafilaria bovicola in Musca xanthomelas and Musca lusoria.

Artificially infected adult flies were used in this study. In both Musca species, P. bovicola developed in the fat-body cells, mainly of the abdomen. Escape from the midgut and penetration of the fat-body cell was possibly achieved by use of the cephalic hook of the microfilaria. At 27 degrees C, development to the 3rd larval stage took 9 days, but maximum length was only reached after 11 days. Sharp increases in larval length took place on Days 6-7 and on Day 9. These sudden increase possibly indicate moults to the 2nd and 3rd larval stages respectively. During larval development the fat-body cell increased markedly in size to from a thin-walled capsule around the larva. On reaching the 3rd stage, larvae escaped from the capsules and migrated to the head cavity and proboscis.

Animals↗
PubMed1998

Avermectin/milbemycin resistance in trichostrongyloid nematodes.

Resistance to levamisole and the benzimidazoles appears to be achieved by one or, at most, two mechanisms in the common trichostrongyloid parasites of sheep. For the avermectin/milbemycin anthelmintic class the picture is more complex. In-vitro assays employing the free-living stages of trichostrongyloid nematodes were used to investigate structure-activity relationships for the avermectins/milbemycins. While avermectin/milbemycin-susceptible isolates of Haemonchus contortus, Trichostrongylus colubriformis and Ostertagia circumcincta were found to differ in their intrinsic sensitivities to avermectin/milbemycin inhibition of larval development and L3 motility, structure-activity profiles against all three species were similar. In-vivo avermectin/milbemycin resistance was associated with a reduced sensitivity to avermectin/milbemycin inhibition of larval motility and/or development in some, but not all, isolates. Where a reduced sensitivity to avermectin/milbemycin inhibition of larval development was observed, different groups of resistant isolates displayed different structure-activity profiles. Many avermectin/milbemycin-resistant isolates showed an increased sensitivity to paraherquamide. These in-vitro data have allowed the classification of avermectin/milbemycin-resistant isolates into a number of distinct types. Study of the inheritance of avermectin/milbemycin resistance in two resistance types suggests that the in-vitro differences between resistant isolates reflect important differences in the mechanism of resistance present. The kinetics of expulsion of H. contortus, T. colubriformis and O. circumcincta from sheep following treatment with ivermectin indicate that, in vivo, the critical action of avermectins/milbemycin against O. circumcincta may be different to that which results in H. contortus and T. colubriformis elimination. This observation provides some explanation for the differences between resistant isolates. If, for different species, the critical event(s) leading to expulsion are different, then it follows that the mechanisms of resistance observed may also differ.

Animals↗
PubMed1976

A comparison of beating parameters in larval and post-larval locomotor systems of the lobster Homarus gammarus (L.).

A study has been made of the interrelations between rhythmical exopodite beating in different larval stages and swimmeret beating in poast-larval stages of the lobster Homarus gammarus. Data on exopodite beat cycle durations have been used for statistical comparisons of exopodite performance within one larva, and also between different stages of larval development. Inter-exopodite comparisons reveal clear bilateral differences (table 1), although there is no consistently favoured relationship (tables 2 and 3). There are significant differences in cycle duration between the first three developmental stages, with a slight increase at the first moult, and a marked decrease at the second (table 4). However, within each stage the repeat frequency exhibits little change (table 5). Therefore it appears that changes in swimming behaviour occur discontinuously in development, and are associated with the larval moults. It is suggested that changes in beat frequency, and especially the faster beating in stage III, may represent responses to changed loading conditions (table 7). Measurements of swimmeret beating in post-larval lobsters have been analysed in terms of cycle durations, and inter- and intra-segmental phase relations. Swimmeret beating patterns are very regular (figure 1), but not restricted to a narrow range of frequencies (table 6a). Intersegmental phase lag remains constant around 0.2 (figure 3) independent of beat frequency (figure 4). Similarly the powerstroke/returnstroke ratio of approximately 0.5 (figure 5) shows no significant correlation with cycle duration (figure 6). Differences emerge in the performance of larval exopodites and post-larval swimmerets (table 6b), although the possibility cannot be excluded that the larval exopodite oscillator in some way influences the developing action of the post-larval swimmeret system.

Age Factors↗