Spatial and temporal changes in the fish communities from a mangrove‐dominated creek system near Karachi,Pakistan

The objectives of the study were to inventory the fish community, examine how the fish communities changed in these creeks temporally (season), and compare the fish communities between creeks of varying structure (width). During February 1999 to December 2001, a survey was undertaken to monitor the distribution and abundance of fishes in the Korangi‐Phitti Creek (KPC) system (24°45′N, 67°20′E) near Karachi, Pakistan. Fish were collected from 123 stations using a combination of monofilament gillnets of 8.9 cm, 5.7 cm, and 3.8 cm stretched mesh sizes. A total of 17 023 fish representing 86 species were collected during the study; Sardinella gibbosa and Nematalosa nasus were the most abundant taxa (in terms of numbers of individuals) collected, accounting for over 60% of the total catch. Physical conditions in the study area were found to have significant seasonal (monsoon) patterns related more to temperature and salinity than to rainfall. Seasonal comparisons indicated that the communities were significantly different between the northeast monsoon (NEM) and southwest monsoon (SWM) seasons. Taxa primarily responsible for distinguishing the NEM were the mullets (Moolgarda cunnesius, Liza carinata, Mugil cephalus). The SWM was characterized by Anodontostoma chacunda, Scomberoides commersonnianus, and the engraulid (Thryssa hamiltonii). The community sampled in wide creeks (shipping channels) was very different in composition than the community in small creeks within this system. Wide creeks were characterized by schooling pelagic species (S. gibbosa, N. nasus), while the smaller creeks were characterized by the presence of mullets (M. cunnesius, M. cephalus, L. carinata) and scat (Scatophagus argus). The KPC system was shown to contain a highly diverse fishery, which in turn contributes to regional offshore fisheries (shad, mackerel, tuna and perches). The various negative natural and anthropogenic events in this region highlight the need for information regarding the fish community, water quality, and the mangrove forest to evaluate ecosystem changes, the effects of disturbances, and for the development and making of sound management decisions.     

DNA Rearrangements Associated with Reversion of Bacteriophage Mu-Induced Mutations

Excision of transposable genetic elements from host DNA is different from the classical prophage lambda type of excision in that it occurs at low frequency and is mostly imprecise; only a minority of excision events restores the wild-type host sequences. In bacteriophage Mu, a highly efficient transposon, imprecise excision is 10-100 times more frequent than precise excision. We have examined a large number of these excision events by starting with mucts X mutants located in the Z gene of the lac operon of Escherichia coli. Mucts X mutants are defective prophages whose excision occurs at a measurable frequency. Imprecise excision was monitored by selecting for melibiose+ (Mel+) phenotype, which requires only a functioning lacY gene. Mel+ revertants exhibit an array of DNA rearrangements and fall in four main classes, the predominant one being comprised of revertants that have no detectable Mu DNA. Most of these revertants can further revert to Lac+. Perhaps 5 base-pair duplications, originally present at prophage-host junctions, are left in these lacZ-Y+ revertants, and they can be further repaired to lacZ+. Another class has, in addition to the loss of Mu DNA, deletions that extend generally, but not always, to only one side of the prophage. The other two classes of revertants, surprisingly, still have Mu DNA in the lacZ gene. One class has deletions in the Z gene, whereas, no deletions can be detected in the other. Many of the revertants in the last class can further revert to lacZ+, indicating that the lacY gene must have been turned on by a rearrangement within Mu DNA. Apparently, all of the detectable precise and most of the imprecise excision events require functioning of the Mu A gene. We suggest that a block in large-scale Mu replication allows the excision process to proceed.     

Using testis size to predict the mating systems of New Zealand geckos

Abstract

The mating system is unknown for the majority of New Zealand geckos (Family Gekkonidae). I investigated interspecific variation in relative testis volume across 19 New Zealand gecko taxa and 63 additional species of squamate reptiles from other countries to make predictions about the social mating system of the New Zealand geckos. Relative testis size varied greatly between species of New Zealand gecko, with testes ranging from 119% larger than expected to 75% smaller than expected. This variation was even greater across other squamates, with testes ranging from 55 to 152% of expected size. This variation could not be explained by seasonality of breeding, clutch size or the sex ratio of populations. As species subject to more intense sperm competition sport relatively larger testes in other vertebrate groups, it is likely that similar variation in gecko testis size is due to differences in mating systems between species. Based on testis volume, it is predicted that at least half of the New Zealand gecko taxa studied are likely to have polygynandrous mating systems.     

Mechanism of neurofibrillary degeneration in Alzheimer's disease

Neurofibrillary degeneration associated with the formation of intraneuronal neurofibrillary tangles of paired helical filaments (PHF) and 2.1 nm τ filaments is one of the most characteristic brain lesions of Alzheimer's disease. The major polypeptides of PHF are the microtubule associated protein, τ. τ, in PHF is present in abnormally phosphorylated forms. In addition to the PHF, the abnormal τ is present in soluble non-PHF form in the alzheimer's disease brain. The level of τ in Alzheimer's disease neocortex is severalfold higher than in aged control brain, and this increase is in the form of the abnormally phosphorylated protein. The abnormally phosphorylated τ does not promote the assembly of tubulin into microtubules in vitro, and it inhibits the normal τ-stimulated microtubule assembly. After in vitro dephosphorylation both PHF and non-PHF abnormal τ stimulate the assembly of tubulin into microtubules. The activities of phosphoseryl/phosphothreonyl protein phosphatase 2A and nonreceptor phosphotyrosyl phosphatase(s) are decreased in AD brain. It is suggested that

1. A defect(s) in the protein phosphorylation/dephosphorylation system is one of the early events in the neurofibrillary pathology in AD;
2. A decrease in protein phosphatase, activities, at least in part, allows the hyperphosphorylation of τ; and
3. Abnormal phosphorylation and polymerization of τ into PHF most probably lead to a breakdown of the microtubule system and consequently to neuronal degeneration.

     

Guanosine Triphosphate Binding to β-Subunit of Tubulin in Alzheimer's Disease Brain: Role of Microtubule-Associated Protein τ

Abstract: In Alzheimer's disease, paired helical filaments composed mainly of abnormally phosphorylated τ accumulate in certain selected neurons of the brain, and microtubules are rarely seen in the affected cells. In the present study, the binding of ³²P-labeled 8-azidoguanosine triphosphate ([γ-³²P]8N₃GTP), the photoaffinity analogue of GTP, to the β-subunit of tubulin in brain homogenates was found to be markedly lower in patients with Alzheimer's disease than in aged control human cases. No significant differences were observed in the levels of the α- and β-subunits of tubulin between Alzheimer's disease and control brains obtained 2–7 h postmortem. In nine of 19 Alzheimer's disease and 11 of 12 control autopsied brains (2–7 h postmortem and stored at ?75°C) tubulin was isolated successfully from brain cytosol by in vitro polymerization induced with DEAE-dextran. The GTP binding was observed in the two cycled assembled microtubule preparations from all the normal control, and in eight of nine Alzheimer's disease cases. Alzheimer's disease microtubule preparations contained varying amounts of abnormally phosphorylated τ, whereas no abnormal τ was detected in the control brain preparations. Addition of bovine τ to bovine, normal human, and Alzheimer's disease brain tubulin preparations markedly increased GTP binding to the β-subunit. An alkaline phosphatase-treated paired helical filament-enriched preparation increased by approximately twofold the GTP binding to bovine brain tubulin. GTP binding to tubulin prepared by phosphocellulose chromatography of two cycled microtubules from three Alzheimer's disease and three normal control brains, revealed insignificant differences between the two groups. These findings have suggested that (1) τ protein promotes the GTP binding to the β-subunit of tubulin, and (2) the breakdown of the microtubule system in brains of patients with Alzheimer's disease might in part be due to the abnormal phosphorylation of τ which depresses the GTP binding.     

Brain Levels of Microtubule-Associated Protein τ Are Elevated in Alzheimer''s Disease: A Radioimmuno-Slot-Blot Assay for Nanograms of the Protein

The microtubule-associated protein tau, which stimulates the assembly of alpha-beta tubulin heterodimers into microtubules, is abnormally phosphorylated in Alzheimer's disease (AD) brain and is the major component of paired helical filaments. In the present study, the levels of tau and abnormally phosphorylated tau were determined in brain homogenates of AD and age-matched control cases. A radioimmuno-slot-blot assay was developed, using a primary monoclonal antibody, Tau-1, and a secondary antibody, antimouse 125I-immunoglobulin G. To assay the abnormally phosphorylated tau, the blots were treated with alkaline phosphatase before immunolabeling. The levels of total tau were about eightfold higher in AD (7.3 +/- 2.7 ng/micrograms of protein) than in control cases (0.9 +/- 0.2 ng/micrograms), and this increase was in the form of the abnormally phosphorylated protein. These studies indicate that the abnormal phosphorylation--not a decrease in the level of tau--is a likely cause of neurofibrillary degeneration in AD.