mando un articolo uscito su the scientist
Non sono assolutamente banali le implicazioni di queste scoperte:
esposizione a chimici danno effetti fino a 4 generazioni. Insomma, un
bel casino per chi pensa che il DNA non si modifica durante la vita
dell'individuo, nonché per chi pensa che gli inquinanti non hanno
effetti a lungo termine. qui stiamo parlando di effetti a lunghissimo
termine. Anche se alcune cose possono essere dette, almeno rispetto
all'homo sapiens: il ciclo vitale dei topi è talmente breve che forse
nell'umano lo stesso effetto può essere nel tempo controbilanciato.
Tuttavia, non possiamo pensare solo in termini di danni per l'umano. le
conseguenze ambientali possono essere devastanti
ciao
m
Toxins harm descendant fertility
Epigenetic effects of endocrine disruptors pass down four
generations in rats
By Philip Hunter <mailto:[EMAIL PROTECTED]>
US researchers have reported firm evidence that damage to mammalian male
fertility caused by transient exposure of embryos to
endocrine-disrupting environmental toxins can be passed down to
subsequent generations. Their finding is published this week
<http://www.sciencemag.org> by /Science/.
Investigators from Washington State University, Pullman, exposed female
rats in mid gestation to two endocrine disruptors, the anti-androgenic
vinclozolin and the estrogenic methoxychlor, both at higher doses than
normally encountered in the environment.
More than 90% of male offspring had low sperm counts and abnormal sperm
production, with 10% being completely infertile. An almost identical
pattern of male fertility impairment was passed down to second-, third-,
and fourth-generation males whose parents were not exposed to the toxins.
The critical process causing the loss of fertility was the DNA
remethylation that always occurs at the time of gonadal sex
determination shaping the patterns of gene expression in the offspring,
said Michael Skinner <http://www.skinner.wsu.edu/>, senior author and
director of the Center for Reproductive Biology at Washington State
University. "The endocrine disruptors appear to have altered the
remethylation and permanently reprogrammed the germ line, that is
sperm," he told /The Scientist/.
The results are significant, said Marcus Pembrey
<http://www.ich.ucl.ac.uk/ich/html/academicunits/clin_mol_gen/c_m_g_staff.html>,
professor of Paediatric Genetics at the Institute of Child Health,
University College London, who wasn't involved in the study. "Yes, it
looks convincing for both the evidence for the transgenerational adverse
effect on spermatogenesis down the male line and the associated
methylation changes in sperm," he told /The Scientist/.
It has been known for at least a decade that some mammal genes are
imprinted with specific DNA methylation patterns
<http://www.biomedcentral.com/pubmed/8755558> that are passed on to
subsequent generations. More recently, there have been several
demonstrations of epigenetic inheritance in mammals. "There are a number
of reports on transgeneration epigenetic inheritance when mice are
exposed during gestation to nutritional methyl donating supplements,
various chemical agents, and ionizing radiation
<http://cmb.duke.edu/faculty/jirtle.html>," said Randy Jirtle
<http://www.the-scientist.com/2004/7/5/14/1>, a radiation oncologist at
Duke University Medical Center, Durham, NC.
The novel aspect of the latest study, he said, was the demonstration
that epigenetic changes caused by endocrine disrupters rather than other
factors, such as radiation exposure, can be inherited by future
generations beyond the immediate offspring.
Skinner said the possibility that the changes in phenotype in male rats
were caused by mutations in DNA rather than methylation changes could be
discounted because if that were the case, the incidence of transmission
to subsequent generations would then be much less, generally under 1%.
Also, the investigators used polymerase chain reaction to identify
changes in the methylation patterns of two genes in rats exposed to
vinclozolin, using methylation-sensitive restriction enzymes. The two
affected genes were lysophospholipase (LPLase), critical in the
synthesis of bioactive lipids and associated signalling, and SH2,
involved in fertility.
An important follow-up will be to assess whether inheritable decline in
fertility shown by the Washington group can be caused by exposure to
endocrine-disrupting toxins at the levels actually prevailing in the
environment, Skinner said. This could be crucial in determining whether
the steep decline in human male sperm counts observed in some countries,
such as the United Kingdom, has been caused by environmental toxins.
Skinner also indicated that males descended from females exposed to the
toxins are more susceptible to other diseases besides impaired
fertility. "Preliminary evidence suggests other diseases develop as the
animals get older," Skinner said. "Examples are prostate disease, kidney
disease, and tumor development. However, these are preliminary results,
and we need to further studies to confirm this."
The work raises the interesting question of whether evolution has
provided a transgenerational mechanism for responding specifically to
potentially damaging environmental factors by reducing but not
completely shutting down male fertility, according to Pembrey. "But it
could also be just a poison that lasts a few generations and then dies
out as eventually selection for precursor cells that don't have the
methylation gets rid of it." Extension of the study over a further few
generations could resolve this, he said.
*Links for this article*
Anway et al., "Epigenetic transgenerational actions of endocrine
disruptors and male fertility," /Science/, 308:1466-9, June 6, 2005.
http://www.sciencemag.org
Michael K. Skinner http://www.skinner.wsu.edu/
Marcus Edred Pembrey
http://www.ich.ucl.ac.uk/ich/html/academicunits/clin_mol_gen/c_m_g_staff.html
S. Saitoh et al., "Minimal definition of the imprinting center and
fixation of a chromosome 15q11-q13 epigenotype by imprinting mutations,"
/PNAS,/ 93:7811-5, July 23, 1996. [PubMed Abstract
<http://www.biomedcentral.com/pubmed/8755558>]
Randy Jirtle http://cmb.duke.edu/faculty/jirtle.html
L.A. Pray, "Epigenetics: Genome, meet your environment," /The
Scientist/, July 5, 2004. http://www.the-scientist.com/2004/7/5/14/1
---
[Quipo ISP - Questa E-mail e' stata controllata dal programma Declude Virus]
[Quipo ISP - This E-mail was scanned for viruses by Declude Virus]
--
www.e-laser.org
Laser@inventati.org
