A familial mutation in the testis-determining gene SRY shared by both sexes

A familial mutation in SRY, the gene coding for the testis-determining factor TDF, was identified in an XY female with gonadal dysgenesis, her father, her two brothers and her uncle. The mutation consists of a T to C transition in the region of the SRY gene coding for a protein motif known as the high mobility group (HMG) box, a protein domain known to confer DNA-binding specificity on the SRY protein. This point mutation results in the substitution, at amino acid position 109, of a serine residue for phenylalanine, a conserved aromatic residue in almost all HMG box motifs known. This F109S mutation was not found in 176 male controls. When recombinant wildtype SRY and SRY^F109S mutant protein were tested in vitro for binding to the target site AAC AAAG, no differences in DNA-binding activity were observed. These results imply that the F109S mutation either is a rare neutral sequence variant, or produces an SRY protein with slightly altered in vivo activity, the resulting sex phenotype depending on the genetic back-ground or environmental factors.This paper is dedicated by G. S. to Professor Ulrich Wolf on the occasion of his 60th birthday     

How reliable are the Powell–Wetherall plot method and the maximum-length approach? Implications for length-based studies of growth and mortality

Length-based methods are the cornerstone of many population studies and stock assessments. This study tested two widely used methods: the Powell–Wetherall (P–W) plot and the L_max approach (i.e., estimating L_∞ directly from L_max). In most simulations, P–W estimates of the ratio total mortality/growth (Z/K ratio) were biased beyond acceptable limits (bias?>?30%). Bias in Z/K showed a complex behavior, without possible corrections. Estimates of asymptotic length (L_∞) were less biased than Z/K, but were very sensitive to intra-cohort variability in growth and to changes in the occurrence of large individuals in the sample. Exclusion of the largest size classes during the regression procedure or weighing by abundance does not solve these issues. Perfect linearization of the data and extremely narrow confidence intervals for Z/K will lead users to erroneous overconfidence in outputs. Clearly, the P–W method is not suitable for the assessment of Z/K ratios of natural populations. Estimation of L_∞ may be tentatively possible under very specific conditions, with necessary external verifications. Also, this study demonstrates that there is no way to estimate L_∞ directly from L_max, since there is no particular relationship to expect a priori between L_∞ and L_max. Errors in estimating L_∞ directly affect the estimate of the growth constant K and all other subsequent calculations in population studies, stock assessments and ecosystem models. New approaches are urgently needed for length-based studies of body growth (e.g., unconstrained curve fit with subsequent bootstrapping), that consider the inherent uncertainty regarding the underlying data and processes.     

Central nervous control of hindleg coordination in stridulating grasshoppers

 Stridulation in many gomphocerine grasshoppers is characterized by specific phase shifts between the two hindlegs as well as different movement patterns produced by the left and the right leg. The underlying neuronal excitation patterns are generated by networks on either side of the metathoracic ganglion. The role of the intraganglionic commissures in right-left coordination and the production of differing movement patterns was investigated by transecting the metathoracic ganglion mediosagittally in Omocestus viridulus, Chorthippus biguttulus and Chorthippus mollis. In all three species, after this operation both hindlegs produced the same pattern and no longer different movements. The effects of transection on coordination differed: rapid movement rhythms, like those typical of Ch. biguttulus and the vibratory parts of the song of Ch. mollis, on the two sides drifted with respect to one another. In contrast, the slow rhythms characteristic of O. viridulus and the song subunits of Ch. mollis were completely synchronized. It is inferred that in intact animals the pathways for coordination of the rapid stridulatory rhythms are exclusively intraganglionic, whereas the phase relations of the slow rhythms are additionally influenced by way of anterior right-left connections, perhaps within the suboesophageal ganglion. Accepted: 15 October 1996     

Aminergic neuron systems of lobsters: morphology and electrophysiology of octopamine-containing neurosecretory cells

In the American lobster (Homarus americanus) the biogenic amines serotonin and octopamine appear to play important and opposite roles in the regulation of aggressive behavior, in the establishment and/or maintenance of dominant and subordinate behavioral states and in the modulation of the associated postural stances and escape responses. The octopamine-containing neurosecretory neurons in the thoracic regions of the lobster ventral nerve cord fall into two morphological subgroups, the root octopamine cells, a classical neurohemal group with release regions along second thoracic roots, and the claw octopamine cells, a group that selectively innervates the claws. Cells of both subgroups have additional sets of endings within neuropil regions of ganglia of the ventral nerve cord. Octopamine neurosecretory neurons generally are silent, but when spontaneously active or when activated, they show large overshooting action potentials with prominent after-hyperpolarizations. Autoinhibition after high-frequency firing, which is also seen in other crustacean neurosecretory cells, is readily apparent in these cells. The cells show no spontaneous synaptic activity, but appear to be excited by a unitary source. Stimulation of lateral or medial giant axons, which excite serotonergic cells yielded no response in octopaminergic neurosecretory cells and no evidence for direct interactions between pairs of octopamine neurons, or between the octopaminergic and the serotonergic sets of neurosecretory neurons was found.     

Dicoumarol Inhibits Multidrug Resistance Protein 1-Mediated Export Processes in Cultured Primary Rat Astrocytes

Dicoumarol is frequently used as inhibitor of the detoxifying enzyme NAD(P)H:quinone acceptor oxidoreductase 1 (NQO1). In order to test whether dicoumarol may also affect the cellular glutathione (GSH) metabolism, we have exposed cultured primary astrocytes to dicoumarol and investigated potential effects of this compound on the cell viability as well as on the cellular and extracellular contents of GSH and its metabolites. Incubation of astrocytes with dicoumarol in concentrations of up to 100 µM did not acutely compromise cell viability nor was any GSH consumption or GSH oxidation to glutathione disulfide (GSSG) observed. However, unexpectedly dicoumarol inhibited the cellular multidrug resistance protein (Mrp) 1-dependent export of GSH in a time- and concentration-dependent manner with half-maximal effects observed at low micromolar concentrations of dicoumarol. Inhibition of GSH export by dicoumarol was not additive to that observed for the known Mrp1 inhibitor MK571. In addition, dicoumarol inhibited also the Mrp1-mediated export of GSSG during menadione-induced oxidative stress and the export of the GSH–bimane-conjugate (GS–B) that had been generated in the cells after exposure to monochlorobimane. Half-maximal inhibition of the export of Mrp1 substrates was observed at dicoumarol concentrations of around 4 µM (GSH and GSSG) and 30 µM (GS–B). These data demonstrate that dicoumarol strongly affects the GSH metabolism of viable cultured astrocytes by inhibiting Mrp1-mediated export processes and identifies for the first time Mrp1 as additional cellular target of dicoumarol.

     

Identification of the ryanodine receptor mutation I4743M and its contribution to diamide insecticide resistance in Spodoptera exigua (Lepidoptera: Noctuidae)

Insect ryanodine receptors (RyRs) are the targets of diamide insecticides. Two point mutations G4946E and I4790M (numbering according to Plutella xylostella, PxRyR) in the transmembrane domain of the insect RyRs associated with diamide resistance have so far been identified in three lepidopteran pests, P. xylostella, Tuta absoluta and Chilo suppressalis. In this study, we identified one of the known RyR target site resistance mutations (I4790M) in a field‐collected population of Spodoptera exigua. The field‐collected WF population of S. exigua exhibited 154 fold resistance to chlorantraniliprole when compared with the susceptible WH‐S strain. Sequencing the transmembrane domains of S. exigua RyR (SeRyR) revealed that the resistant WF strain was homozygous for the I4743M mutation (corresponding to I4790M in PxRyR), whereas the G4900E allele (corresponding to G4946E of PxRyR) was not detected. The 4743M allele was introgressed into the susceptible WH‐S strain by crossing WF with WH‐S, followed by three rounds of backcrossing with WH‐S. The introgressed strain 4743M was homozygous for the mutant 4743M allele and shared about 94% of its genetic background with that of the recipient WH‐S strain. Compared with WH‐S, the near‐isogenic 4743M strain showed moderate levels of resistance to chlorantraniliprole (21 fold), cyantraniliprole (25 fold) and flubendiamide (22 fold), suggesting that the I4743M mutation confers medium levels of resistance to all three diamides. Genetic analysis showed diamide resistance in the 4743M strain was inherited as an autosomal and recessive trait. Results from this study have direct implications for the design of appropriate resistance monitoring and management practices to sustainably control S. exigua.