Approaches for identifying germ cell mutagens: Report of the 2013 IWGT workshop on germ cell assays☆

Abstract

This workshop reviewed the current science to inform and recommend the best evidence-based approaches on the use of germ cell genotoxicity tests. The workshop questions and key outcomes were as follows. (1) Do genotoxicity and mutagenicity assays in somatic cells predict germ cell effects? Limited data suggest that somatic cell tests detect most germ cell mutagens, but there are strong concerns that dictate caution in drawing conclusions. (2) Should germ cell tests be done, and when? If there is evidence that a chemical or its metabolite(s) will not reach target germ cells or gonadal tissue, it is not necessary to conduct germ cell tests, notwithstanding somatic outcomes. However, it was recommended that negative somatic cell mutagens with clear evidence for gonadal exposure and evidence of toxicity in germ cells could be considered for germ cell mutagenicity testing. For somatic mutagens that are known to reach the gonadal compartments and expose germ cells, the chemical could be assumed to be a germ cell mutagen without further testing. Nevertheless, germ cell mutagenicity testing would be needed for quantitative risk assessment. (3) What new assays should be implemented and how? There is an immediate need for research on the application of whole genome sequencing in heritable mutation analysis in humans and animals, and integration of germ cell assays with somatic cell genotoxicity tests. Focus should be on environmental exposures that can cause de novo mutations, particularly newly recognized types of genomic changes. Mutational events, which may occur by exposure of germ cells during embryonic development, should also be investigated. Finally, where there are indications of germ cell toxicity in repeat dose or reproductive toxicology tests, consideration should be given to leveraging those studies to inform of possible germ cell genotoxicity.

Single-molecule PCR analysis of an unstable microsatellite for detecting mutations in sperm of mice exposed to chemical mutagens

“…This method can be applied potentially to environmental biomonitoring using sentinel species and to human populations to assess the effects of variables that influence heritable mutagenesis [1,4,33,[60][61][62][63][64][65][66]. Our new method expands our ability to detect mutations in germ cells, but we must consider the diverse types of mutation mechanisms and continue to expand the mutational landscape that we can capture in toxicological screening [67].…”

Germline mutation rates and the long-term phenotypic effects of mutation accumulation in wild-type laboratory mice and mutator mice

“…More recently, the importance of understanding the risks and effects of germline mutagens, such as environmental chemicals and radiation, on the future health of animal populations, including humans, has become clear (Yauk et al 2015). However, only limited information about the long-term effects of mutation-rate differences is currently available.…”

The effects of extremely low frequency magnetic fields on mutation induction in mice

“…Ultimately, through the use of seven easily recognisable visible markers, the SLT provides a platform through which the transmission of novel and heritable gene mutations can be scored. Indeed, the main strength of this assay is that it analyses the transferal of novel germline mutations in the offspring of treated parents, which simulates the genetic changes associated with heritable human genetic diseases (reviewed in Yauk et al, (2015)). …”

“…As such, females demonstrating signs of mating are sacrificed approximately seventeen days post-conception, upon which the ovaries and uterine contents are assessed. The amount of ovulated eggs is determined via counting corpora lutea, in addition to the number of viable and dead implanted embryos (reviewed in Yauk et al, (2015)) and the number of implants (living vs dead) against the number of eggs ovulated per pregnant female for both the treated and control groups. The dominant lethal effect is then calculated by comparing the data for the treated and control groups against one another.…”

“…Moreover, human minisatellites do not exhibit the same levels of somatic instability as ESTR loci (Jeffreys et al, 1988(Jeffreys et al, , 1994. This may cast doubts over the biological relevance of ESTR assays and their substitution for human minisatellite instability (reviewed in (Bouffler et al, 2006;Singer & Yauk, 2010;Yauk et al, 2015)). …”