Chronic metal contamination shapes the size structure of Gammarus fossarum populations in French headwater rivers.

Assessing the effects of multigenerational exposure of aquatic animal populations to chemical contamination is essential for ecological risk assessment. However, beyond rare examples reporting the sporadic emergence of a toxicological tolerance within populations that persist in contaminated environments, conclusive results are even more limited from field studies when it comes to the alteration of life-history traits. Here, we investigated whether long-term exposure to cadmium (Cd) influences size-related life-history traits (i.e., size at puberty, median adult size, maximum size) in Gammarus fossarum, a keystone species of European stream ecosystems. We studied 13 field populations of G. fossarum (cryptic lineage B) living in headwater rivers located in natural areas scattered at a large geographical scale and exposed to contrasted bioavailable Cd contamination levels due to different local geochemical backgrounds. We achieved a detailed description of the physical and physicochemical conditions of the river reaches investigated. Land-use parameters, hydrological characteristics (flow, slope, river width, flow structure, mosaic of substrates), and physicochemical conditions (temperature, conductivity, dissolved oxygen) were measured. Metallic bioavailable contamination was assessed using a standardized active biomonitoring procedure (Gammarus caging). Based on the field demographic census of the 13 populations, our results demonstrated that chronic Cd contamination significantly influences life-history in the G. fossarum species, with a significant reduction in all size traits of populations (size at puberty, median adult size, maximum size). In addition, we confirmed Cd-tolerance in contaminated populations during exposure tests in the laboratory. Various hypotheses can be then put forward to explain the modification of size-related life-history traits: a direct toxic effect of Cd, a cost of Cd-tolerance, or an adaptive evolution of life-history exposed to toxic pressure.

Notch pathway repression by vestigial is required to promote indirect flight muscle differentiation in Drosophila melanogaster.

Drosophila dorsal longitudinal muscles develop during metamorphosis by fusion of myoblasts with larval templates. It has been shown that both vestigial and Notch are crucial for correct formation of these muscles. We investigated the relationship between vestigial and the Notch pathway during this process. Using Enhancer of Split Region Transcript m6 gene expression as a reporter of Notch pathway activity, we were able to demonstrate that this pathway is only active in myoblasts. Moreover, close examination of the cellular location of several of the main actors of the N pathway (Notch, Delta, neuralized, Serrate, Mind bomb1 and fringe) during dorsal longitudinal muscle development enabled us to find that Notch receptor can play multiple roles in adult myogenesis. We report that the locations of the two Notch ligands (Delta and Serrate) are different. Interestingly, we found that fringe, which encodes a glycosyltransferase that modifies the affinity of the Notch receptor for its ligands, is expressed in muscle fibers and in a subset of myoblasts. In addition, we demonstrate that fringe expression is essential for Notch pathway inhibition and muscle differentiation. Lastly, we report that, in vestigial mutants, fringe expression is lost, and when fringe is overexpressed, a significant rescue of indirect flight muscle degeneration is obtained. Altogether, our data show that a vestigial-differentiating function is achieved through the inhibition of the Notch pathway.

Control of apterous by vestigial drives indirect flight muscle development in Drosophila.

Drosophila thoracic muscles are comprised of both direct flight muscles (DFMs) and indirect flight muscles (IFMs). The IFMs can be further subdivided into dorsolongitudinal muscles (DLMs) and dorsoventral muscles (DVMs). The correct patterning of each category of muscles requires the coordination of specific executive regulatory programs. DFM development requires key regulatory genes such as cut (ct) and apterous (ap), whereas IFM development requires vestigial (vg). Using a new vg(null) mutant, we report that a total absence of vg leads to DLM degeneration through an apoptotic process and to a total absence of DVMs in the adult. We show that vg and scalloped (sd), the only known VG transcriptional coactivator, are coexpressed during IFM development. Moreover, we observed an ectopic expression of ct and ap, two markers of DFM development, in developing IFMs of vg(null) pupae. In addition, in vg(null) adult flies, degenerating DLMs express twist (twi) ectopically. We provide evidence that ap ectopic expression can induce per se ectopic twi expression and muscle degeneration. All these data seem to indicate that, in the absence of vg, the IFM developmental program switches into the DFM developmental program. Moreover, we were able to rescue the muscle phenotype of vg(null) flies by using the activity of ap promoter to drive VG expression. Thus, vg appears to be a key regulatory gene of IFM development.

Neurobiological effects of a null mutation depend on genetic context: comparison between two hotfoot alleles of the delta-2 ionotropic glutamate receptor.

Hotfoot is a mutant mouse with an ataxic phenotype which has been shown to be due to a mutation in the Grid2 gene. In this paper, we compare molecular, morphological, electrophysiological and behavioral features of two Grid2 alleles: Grid2(ho-4J) and Grid2(ho-Nancy). We first show that these two mutations are deletions in the open reading frame of the gene and that no GRID2 protein is detectable in extracts of mutant cerebella, suggesting that the two alleles are null-like mutations. Morphological and electrophysiological analyses reveal no obvious differences between the two strains: both strains showed the naked Purkinje dendritic spines and mismatch between the length of the presynaptic active zone and postsynaptic differentiation characteristic of the hotfoot mutation; and the same low level (20%) of multiple climbing fiber innervation of Purkinje cells was found in both strains. Only differences in motor behavior were found between the two strains. The Grid2(ho-4J) mouse shows more severe ataxia that the Grid2(ho-Nancy) mouse and, although both strains show a clear capacity to improve their performance of a motor task with training, the Grid2(ho-4J) performance remains very poor whereas Grid2(ho-Nancy) mice approach control levels. The only difference between the two strains is their genetic background. Our results show that the genetic background must be taken into account when analyzing sensorimotor performances of mutant mice.

Hotfoot mouse mutations affect the delta 2 glutamate receptor gene and are allelic to lurcher.

Hotfoot (ho) is a recessive mouse mutation characterized by cerebellar ataxia associated with relatively mild abnormalities of the cerebellum. It has been previously mapped to Chromosome 6, and at least eight independent alleles have been reported. Here we show that the hotfoot phenotype is associated with mutations in the glutamate receptor ionotropic delta2 gene (Grid2). We have identified a 510-bp deletion in the Grid2 coding sequence in the ho4J allele, resulting in a deletion of 170 amino acids of the extracellular domain of the receptor. Analysis of a second allele, hoTgN37INRA, revealed a 4-kb deletion in the Grid2 transcript. The GRID2 protein in these hotfoot mutants probably has a reduced (or null) activity since the phenotype of hotfoot bears similarities with the previously described phenotype of Grid2 knockout mice. The exceptionally high number of independent alleles at the ho locus is an invaluable tool for investigating the function of the glutamate receptor ionotropic delta2 protein, which so far remains largely unknown.

Construction of a high-resolution genetic map encompassing the hotfoot locus.

Hotfoot (ho) is a mutation affecting posture and movement. We report a new allele associated with the insertion of a transgene and its high-resolution mapping. Analysis of the transgene revealed that two complete and two truncated copies are inserted at the ho locus. The ho locus cosegregated with D6Mit299 in 702 meioses and is confined to a 1.1-cM region between the markers D6Mit122 and D6Mit174. If the order and distances between markers are consistent with previously published mapping data, the position of the ho locus must be revised and placed approximately 30 cM from the centromere. This high-resolution genetic map is the first step towards the positional cloning of the ho mutation.

Vesicle formation and follicular root sheath separation in mice homozygous for deleterious alleles at the balding (bal) locus.

The balding (bal) mutation of the mouse is an autosomal recessive mutation that causes alopecia and immunologic anomalies. A new allele was identified by allelism testing after using an interspecific backcross to localize the mutation to the centromeric end of mouse chromosome 18. We investigated the skin and hair histologic lesions of two alleles (bal(J) and bal(Pas)) at this locus and analyzed the expression of several keratinocyte markers and the production of autoantibodies by immunofluorescence on frozen skin sections. The lesions observed included separation of the inner and outer root sheath in anagen follicles resulting in the hair fiber being very easily plucked from the follicle. Vesicles on the ventral tongue, mucocutaneous junction of the eyelid, foot pads, and rarely in skin were also evident. Separation occurred between the basal and suprabasilar cells forming an empty cleft, resembling that observed in human pemphigus vulgaris. Immunofluorescence studies did not reveal the presence of tissue-bound or circulating autoantibodies. Expression of keratinocyte markers in hair follicles was normal. Keratin 6-positive cells were found on either side of the follicular separation suggesting a molecular defect in adhesion molecules between the inner layer of the outer root sheath cells to layers on either sides. This hypothesis has been confirmed by another group who demonstrated that the bal(J) mutation is due to the insertion of a thymidine in the desmoglein 3 gene, resulting in a premature stop codon.

Male sterility caused by sperm cell-specific structural abnormalities in ebouriffé, a new mutation of the house mouse.

We have investigated the male sterility associated with a new recessive mutation of the house mouse: ébouriffé (ebo). All spermatozoa present in the epididymis showed severe malformations, mostly of the tail. Light and electron microscopy showed a drastic decrease of the spermatid population, whereas spermatogonia and spermatocytes seemed moderately affected. This suggests that the mutation affects mostly spermiogenesis. Defects appeared during formation of the acrosome: the acrosomal granule was frequently vacuolated at stages II-III, giving rise first to abnormal acrosomes (stages VI-VII) with dilations and perforations, and then to an abnormal head and acrosome shape (stages IX-XI). However, the most common malformations affected the flagella in elongated spermatids. Sometimes the centriole doublet did not move into the implantation fossa, causing an unattached and isolated flagellum. The major defect occurred in the midpiece region of differentiating spermatozoa: flagellar components were present but highly disorganized, and mitochondria were aggregated in a compact mass. Even though we have no evidence that the ebo gene is a testis structural gene or a regulatory gene that disrupts the complex spermatogenesis process, this mutation may provide an interesting tool for studying the late stages of spermatogenesis. Using an interspecific backcross, we localized the ebo mutation on chromosome 2, with no recombination out of 44 meioses with locus D2Mit32.

Lanceolate hair (lah): a recessive mouse mutation with alopecia and abnormal hair.

A new autosomal recessive mutation of the house mouse developed generalized alopecia associated with breakage of abnormal hair shafts. This mutation, named 'lanceolate hair' (symbol: lah), arose in a mutagenesis experiment using ethylnitrosourea. Hair shafts were short with a focal degeneration at the breakpoint characterized by a pronounced enlargement at the apex, resembling a lance head. Plucked hair fibers were 2.0 to 3.5 mm in length with a normal base, suggesting that there was a synchronized developmental defect. Histologic examination of anagen follicles revealed abnormal cornification of the matrix region with degeneration resulting in the focal hair shaft deformity. Catagen follicles showed pronounced follicular dystrophy but telogen follicles were almost normal. There was a marked, persistent thickening of the epidermis associated with a non-scarring, relatively non-inflammatory ichthyosiform dermatitis. These features are found in the Netherton's syndrome of the human, for which this mouse mutation may represent a model. The lah mutation has been localized to the centromeric end of mouse Chromosome 18.

aku, a mutation of the mouse homologous to human alkaptonuria, maps to chromosome 16.

Alkaptonuria is a human hereditary metabolic disease characterized by a very high urinary excretion of homogentisic acid, an intermediary product in the metabolism of tyrosine, in association with ochronosis and arthritis. This disease is due to a deficiency in the enzyme homogentisic acid oxidase and is inherited as an autosomal recessive condition. We have found a new recessive mutation (aku) in the mouse that is homologous to human alkaptonuria, during a mutagenesis program with ethylnitrosourea. Affected mice show high levels of urinary homogentisic acid without signs of ochronosis or arthritis. This mutation has been mapped to Chr 16 close to the D16Mit4 locus, in a region of synteny with human 3q.