Functional significance of genotoxicity in fish germ cells

The aquatic environment is becoming increasingly contaminated by pollutants having a genotoxic potential towards organisms and in particular in fish. Such genotoxins are prone to affect directly offspring or indirectly through the reproductive process. All this could influence recruitment rate and hence the population dynamics. However, assessment of the ecological risks associated with environmental genotoxic exposure is usually based on individual responses. Thus, there is a need for a better understanding of the long term and population level implications of genotoxic insults in fish. While low levels of DNA damage in somatic cells and oocytes can be efficiently repaired, mature sperm cells, i.e. spermatozoa, are susceptible to accumulate damage due to their lack of repair capacity. The present work aims to track the transfer of toxic effects across generations by studying the link between the level of DNA damage in fish sperm, and the rate of development abnormalities measured in the offspring after parental exposure to the model genotoxicant MMS. Three different fish species were chosen based either on their ecological importance or on their reproduction behavior, respectively brown trout (Salmo trutta), Arctic charr (Salvelinus alpinus) and threespine stickleback (Gasterosteus aculeatus). Results show a significant increase in sperm DNA damage measured with the comet assay in exposed organisms. This damage did not impact on fertilization success but led further to a significant increase in embryo abnormality rate at early embryonic and late larval stages, and further delayed growth in exposed group compared to the control

Reproduction impairment following paternal genotoxin exposure in brown trout (Salmo trutta) and Arctic charr (Salvelinus alpinus)

International audienceThis work describes some consequences of paternal germ cell DNA damage on the reproduction success in two fish species. Male brown trout (n = 31) and male Arctic charr (n = 28) were exposed to the model genotoxicant MMS at the end of spermatogenesis to generate a significant DNA damage level in mature spermatozoa (28% and 25% tail DNA in trout and charr sperm, respectively, evaluated through the comet assay). Sperm from each MMS exposed and control fish was then used to fertilize in vitro an aliquot of a single pool of eggs collected from 4 unexposed females for each species. Each batch of fertilized eggs was monitored individually in the hatchery to follow embryonic and larval abnormalities during the fry development. Paternal exposure did not influence fertilization rate or survival rate at hatching in either species. However, MMS paternal treatment resulted in a large array of morphological abnormalities during embryonic and larval development. At the eyed stage, malformations exhibited a 8 fold increase in trout and a 2 fold increase in charr for larvae stemming from MMS treated males as compared with controls. At the end of yolk sac resorption, an increase in the gross morphological abnormality incidence was found in trout larvae originating from MMS exposed males (2.10% vs. 0.93% in control, p < 0.05). When looking more in detail at bony structures after Alizarin red S staining, a 20% incidence of skeletal defects was recorded at the swimming stage. A positive correlation was found between the paternal sperm DNA damage level and the skeletal abnormality incidence of its progeny. During the next 2 months of development, mortality in trout originating from DNA damaged sperm was 3 times higher than in control. After one year, no effect of paternal treatment was found on growth traits (length and weight) but the gross morphological abnormality incidence was still very high in the treated group (27% malformation incidence vs. 0.5% in control). These results demonstrate ecologically relevant consequences of fish spermatozoa DNA damage and stress the value of using this parameter as a biomarker signaling potential long term effects of environmental genotoxins in aquatic systems

Attempt to link paternal genotoxic exposure to reproductive impairment in fish

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