NPG;Hoe en wat van de muizen

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1 Korte samenvatting van de onderstaande tekst
2 Genetically Engineered Mice Reach Adulthood via 'Virgin Birth
3 In a First for Mammals, Mice Are Created Without Fathers
4 - N a v i g a t i e -

[edit] Korte samenvatting van de onderstaande tekst

De muizen genoemd in dit artikel zijn "verwekt" via een zogenaamde "maagdelijke geboorte". Gentechnologie wordt bijna Bijbels op deze manier.
Het eitje van de moedermuis wordt tot ontwikkeling gebracht zonder tussenkomst van de vader of zijn sperma inbreng. Ook met kikkers zijn zulke experimenten gedaan in het verleden. Experimenten gedaan met mensen embryo's en Apen op deze wijze zijn tot op heden niet gelukt. Het blijkt dat de placenta zich langzaam ontwikkeld zonder "de inbreng" van het manlijk sperma en na enkele dagen stopt het experiment.
Dit geeft aan waarom onderzoekers in de hier geschetste en geslaagde versie zo geinteresseerd zijn. De kernvraag is namenlijk; Waarin zit hem het verschil! Waarom lukt het bij een muis wel, en bij een aap of mens niet. Wat is de inbreng van het mannelijke? Dit raakt aan zeer wezenlijke principes in mens en dier.
Hieronder kunt u de volledige tekst vinden in het Engels alsmede enkele bronverwijzingen.(NPG)

Bron; my.webmd.com Bronnen; Kono, T. Nature, April 22, 2004; vol 428: pp 860-864. Patrick Tam, PhD, senior principal research fellow, Children's Medical Research Institute, University of Sydney, Australia. Kent. E. Vrana, PhD, Elliot S. Vesell Professor; chair of pharmacology, Penn State College of Medicine, Hershey, Pa.

[edit] Genetically Engineered Mice Reach Adulthood via 'Virgin Birth

By Sid Kirchheimer

WebMD Medical News Reviewed By Brunilda Nazario, MD

on Wednesday, April 21, 2004

April 21, 2004 -- If research in mice holds true, men -- and hence, their manly services -- may no longer be needed.

At least that's the indication of a new study boasting a scientific first: Mice that reached adulthood through parthenogenesis, a form of reproduction in which the female egg develops into a live birth without male fertilization.

Parthenogenesis, from the Greek word for "virgin birth," is old hat for egg-laying species such as insects, fish, and lizards. With these species, which ironically includes some birds and bees (the very symbol for the more traditional way of making babies), females produce eggs, but they develop without any help or need of would-be fathers.

Yet no mammal has ever been known to give birth through parthenogenesis, and previous mice, monkeys, and human embryos created this way have never survived for more than a few days. One major reason: In mammals fathers remain a necessity. Without the genetic material from sperm the placenta develops poorly and the embryo cannot survive. The placenta provides oxygen and nutrients to developing embryos.

Does this suggest that other male mammals -- namely, us -- will lose some of our baby-making value? Rest easy, guys, and don't shelve those Barry White tunes just yet. "This is not going to be a straight-forward technique to enable parthenogenetic reproduction of a mammalian species," Australian embryologist Patrick Tam, PhD, tells WebMD. He says that the mice used in his study were not ordinary mice. These mice contained a specifically engineered gene that altered the activity of the other chromosomes.

Indeed. These mice developed from eggs that contained only maternal genetic material, unlike other mammals which develop through sexual reproduction and contain genetic material from both parents.

In the study the researchers combined chromosomes from cells with a missing key "male" gene -- called H19 -- with chromosomes from a fully grown egg which contains only maternal genes. In the past, embryos created this way died shortly before birth because of a poorly developed placenta. This time the researchers were able to create mice that developed normally and survived for much longer. One of the new pups was even able to reproduce after reaching adulthood. The report appears in this week's Nature.

"These findings provide the most compelling genetic evidence that it is absolutely essential to maintain some differences in the activity of genes from the father and the mother for the embryo to grow and develop," says Tam, who wrote an accompanying editorial in Nature but was not involved in the Japanese study. "This phenomenon is called 'genomic imprinting,' whereby the same gene may be marked differently for function depending on from which parent it is inherited."

That's important because it could lead to a better understanding about why some human pregnancies fail during the first trimester, says parthenogenesis expert Kent E. Vrana, PhD, of Penn State College of Medicine.

"What these researchers found is that in developing mice, parthenogenesis may typically fail at day 10, mid-gestation. But when they tweak the genes, they could get it to day 13. They tweak genes again and reach day 17, and tweak again and get the mice to full-term," he tells WebMD. Full-term pregnancy for mice is typically 19 to 31 days.

"This research is not going to provide a tool to create new clones or develop stem cell technologies, but it does provide new information on embryo development," says Vrana, who chairs the pharmacology department. "With better understand of how embryo development works, we could better understand how to correct it when it doesn't -- and better understand why some pregnancies fail early on."

Bron; agonist.org Experimenten in Japan GENETICS:MICE CREATED WITHOUT FATHERS « on: April 22, 2004, 12:22:59 am »

[edit] In a First for Mammals, Mice Are Created Without Fathers

By Rick Weiss Washington Post Staff Writer Wednesday, 21 April 2004
Scientists in Japan have coaxed mouse eggs to grow into apparently healthy mice without being fertilized first by sperm, marking the first creation of mammals from individual egg cells without any contribution from a father.

The advance, described in a report being published today, is the latest in a series of reproductive innovations that, in laboratories at least, have begun to make old-fashioned sexual procreation seem almost quaint.

Lacking any paternal genes, all the mice born this way were females. But they are not clones, because each is a genetically unique animal developed from its own egg. The feat does not suggest that men will soon become irrelevant for human reproduction. The extreme genetic manipulations used by the team are for now, at least, technically and ethically infeasible in humans. The experiments produced far more dead and defective baby mice than normal ones.

But experts said the work breaks important new ground by decoding the biological signaling system that tells a developing embryo whether it has received DNA from a female and a male -- normally a requirement for mammals -- and shows how that system can be circumvented to "fool" an egg into thinking it has been fertilized.

If simpler techniques for bypassing the male-and-female requirement emerge, scientists said, humans may someday gain the option that some insects, lizards, amphibians and other animals have: parthenogenesis, or the direct and unassisted production of daughters from mothers.

"It's probably not an insurmountable problem," said Harvard biologist David Haig. "Then you're faced with the issue of 'Is this something you want to do?' And I'm sure there would be some very strong opinions on that."

The new work, led by Tomohiro Kono, a developmental biologist at Tokyo University of Agriculture, focused on a mysterious aspect of mammalian reproduction called genomic imprinting. In that process, which takes place inside developing eggs and sperm, tiny molecules attach themselves to certain genes and effectively turn those genes off. Through a mechanism that remains poorly understood, different genes are shut down in sperm than in eggs.

Because a full set of working genes is needed for development, pairs of eggs or pairs of sperm cannot grow into new animals. Only when egg and sperm join forces will a young embryo have the right collection of working and non-working genes.

Scientists want to understand the process, because some diseases are caused by faulty imprinting. Others want to make human embryos by parthenogenesis as a source of medically useful stem cells.

Kono's approach was, in essence, to remove various snippets of DNA from egg cells until he got to the point where the egg developed into a healthy fetus by itself -- evidence that the DNA he had eliminated contained the central instructions for imprinting.

He worked with eggs that had been engineered to contain DNA from two different female mice -- in part, to make up for the DNA that would normally be provided by a sperm -- and he focused on a gene called H19, which he had fingered as a likely imprinting "master gene."

In previous efforts, Kono had placed eggs that were missing a small part of that gene into the wombs of surrogate mother mice and marveled as they developed into fetuses for 17.5 days -- just two days short of full-term gestation.

In today's issue of the journal Nature, his team reports that when the H19 gene was even more disabled, several mice developed fully. One, named Kaguya, after a Japanese folk tale in which a princess is born from a bamboo stump, grew to adulthood and has become a mother herself -- though by conventional means continues: wapo next page -> zie de link bovenaan dit artikel

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