cellule adulte che regrediscono a staminali

Secondo quanto pubblicato su Nature, due team di ricercatori, uno canadese e uno britannico, sono riusciti a sviluppare un nuovo tipo di cellule staminali indotte (Ips) pluripotenti. Il nuovo sistema è eticamente compatibile perche’ le staminali sono ottenute riprogrammando cellule adulte e non attraverso lo sviluppo di embrioni. Inoltre, è più sicuro in quanto non sono stati utilizzati virus per far regredire le cellule adulte. Le cellule staminali ottenute sono pluripotenti quindi in grado di trasformarsi in qualsiasi tessuto umano.

La tecnica di regressione, sviluppata nel 2007 dal giapponese Shinya Yamanaka dell’universita’ di Kyoto, prevedeva l’uso di virus che benche’ resi inoffensivi potevano comunque causare alterazioni e anomalie nello sviluppo delle cellule indotte. Nella nuova modalità, i quattro geni capaci di far regredire le cellule adulte in staminali, sono stati inseriti utilizzando, anziche’ un virus, uno speciale vettore molecolare chiamato ‘piggyBac’: si tratta di una sequenza di materiale genetico (trasposone) capace di spostarsi da una posizione all’altra del genoma.

La nuova tecnica e’ stata messa a punto a Toronto da Andras Nagy e in Scozia da Keisuke Kaji, del Centro di medicina rigenerativa dell’universita’ di Edimburgo. Le staminali cosi’ ottenute potranno essere impiegate per rigenerare organi e tessuti umani danneggiati.
www.staminali.eu/index.php/nuovo-sistema...erare-staminali-ips/

Sono un po' scettico, ma i trasposoni non sono elementi genomici instabili che possono duplicarsi e saltare a piacimento? Mi piacerebbe saperne di più e capire se e come li hanno stabilizzati...

Sono un po' scettico, ma i trasposoni non sono elementi genomici instabili che possono duplicarsi e saltare a piacimento? Mi piacerebbe saperne di più e capire se e come li hanno stabilizzati...

purtroppo non ho l'abbonamento a nature, per cui posso postare solo l'abstract e qualcosa che ho trovato su internet:

[size=12pt]piggyBac transposition reprograms fibroblasts to induced pluripotent stem cells[/size]

Knut Woltjen1, Iacovos P. Michael1,2, Paria Mohseni1,2, Ridham Desai1,2, Maria Mileikovsky1, Riikka Hämäläinen1, Rebecca Cowling1, Wei Wang3, Pentao Liu3, Marina Gertsenstein1, Keisuke Kaji4, Hoon-Ki Sung1 & Andras Nagy1,2

Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario M5G 1X5, Canada
Department of Molecular Genetics, University of Toronto, Toronto M5S 1A8, Canada
The Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridgeshire CB10 1SA, UK
MRC Centre for Regenerative Medicine, Institute for Stem Cell Research, University of Edinburgh, Edinburgh EH9 3JQ, UK
Correspondence to: Andras Nagy1,2 Correspondence and requests for materials should be addressed to A.N. (Email: nagy@lunenfeld.ca).


Transgenic expression of just four defined transcription factors (c-Myc, Klf4, Oct4 and Sox2) is sufficient to reprogram somatic cells to a pluripotent state. The resulting induced pluripotent stem (iPS) cells resemble embryonic stem cells in their properties and potential to differentiate into a spectrum of adult cell types. Current reprogramming strategies involve retroviral, lentiviral, adenoviral and plasmid transfection to deliver reprogramming factor transgenes. Although the latter two methods are transient and minimize the potential for insertion mutagenesis, they are currently limited by diminished reprogramming efficiencies. piggyBac (PB) transposition is host-factor independent, and has recently been demonstrated to be functional in various human and mouse cell lines. The PB transposon/transposase system requires only the inverted terminal repeats flanking a transgene and transient expression of the transposase enzyme to catalyse insertion or excision events. Here we demonstrate successful and efficient reprogramming of murine and human embryonic fibroblasts using doxycycline-inducible transcription factors delivered by PB transposition. Stable iPS cells thus generated express characteristic pluripotency markers and succeed in a series of rigorous differentiation assays. By taking advantage of the natural propensity of the PB system for seamless excision, we show that the individual PB insertions can be removed from established iPS cell lines, providing an invaluable tool for discovery. In addition, we have demonstrated the traceless removal of reprogramming factors joined with viral 2A sequences delivered by a single transposon from murine iPS lines. We anticipate that the unique properties of this virus-independent simplification of iPS cell production will accelerate this field further towards full exploration of the reprogramming process and future cell-based therapies.

Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario M5G 1X5, Canada
Department of Molecular Genetics, University of Toronto, Toronto M5S 1A8, Canada
The Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridgeshire CB10 1SA, UK
MRC Centre for Regenerative Medicine, Institute for Stem Cell Research, University of Edinburgh, Edinburgh EH9 3JQ, UK
Correspondence to: Andras Nagy1,2 Correspondence and requests for materials should be addressed to A.N. (Email: nagy@lunenfeld.ca).
www.nature.com/nature/journal/v458/n7239/full/nature07863.html

[size=12pt]
Stem Cell Breakthrough: Pluripotency Without Using Viruses[/size]

Scientists from Canada and the UK have found a new way to create stem cells without using viruses to introduce genetic material into the nuclei to make the cells pluripotent, instead they insert four genes that reprogram the cells then remove them later. The researchers said their work could lead to possible cures for a range of degenerative diseases that destroy tissue, such as spinal cord injury, macular degeneration, diabetes and Parkinson's disease.

The researchers in Canada were from the Samuel Lunenfeld Research Institute at Mount Sinai Hospital in Toronto, Ontario and the Department of Molecular Genetics at the University of Toronto, and the researchers in the UK were from the The Wellcome Trust Sanger Institute in Hinxton, Cambridgeshire, and the MRC Centre for Regenerative Medicine at the Institute for Stem Cell Research in the University of Edinburgh. The study is published in an advanced online 1 March issue of Nature.

The researchers found that introducing just four genes that act as transcription factors, called c-Myc, Klf4, Oct4 and Sox2 was enough to reprogram cells from adult tissue into pluripotent cells.

The pluripotent cells resembled embryonic stem cells in that they acquired the potential to differentiate into a wide range of adult cell types.

The current method for achieving this relies on using viruses (such as retroviruses, lentiviruses and adenoviruses) and plasmids (small pieces of DNA that self-replicate like viruses inside host cells) that introduce genetic material to induce pluripotency.

Retroviruses and lentiviruses bring with them the risk that they will damage host cell DNA and unleash uncontrolled cell growth, rather like cancer, and while the other two, lentiviruses and plasmids don't, they have limited reprogramming potential.

So given these disadvantages, finding a new way to induce pluripotency without disrupting healthy genes is a real breakthrough in adult stem cell science, diminishing reliance on embryonic stem cells, which is controversial because it involves the destruction of embryos.

Senior author Dr Andras Nagy, who is a Senior Investigator at the Samuel Lunenfeld Research Institute of Mount Sinai Hospital, an Investigator at the McEwen Centre for Regenerative Medicine, and Canada Research Chair in Stem Cells and Regeneration, said:

"We hope that these stem cells will form the basis for treatment for many diseases and conditions that are currently considered incurable."

"This new method of generating stem cells does not require embryos as starting points and could be used to generate cells from many adult tissues such as a patient's own skin cells," he added.
Nagy and colleagues used a new "wrapping" method to deliver the four transcription factor genes into the adult cells to reprogram then into stem cells. They wrote that this method, which is called "piggyBac (PB) transposition" is "host-factor independent, and has recently been demonstrated to be functional in various human and mouse cell lines".

In this study the researchers were able to show successful and efficient reprogramming of mouse and human fibroblasts taken from embryonic stem cell lines, but there is no reason in principle why this could not happen to fibroblasts taken from adult tissue.

The stable pluripotent cells they created displayed all the characteristic markers of pluripotency and succeeded in a "series of rigorous differentiation assays".

Nagy and colleagues also showed it was possible to remove the PB wrapping seamlessly from established pluripotent cell lines, which gives scientists an important tool for research.

They concluded that:

"We anticipate that the unique properties of this virus-independent simplification of iPS [induced pluripotent stem] cell production will accelerate this field further towards full exploration of the reprogramming process and future cell-based therapies."

An important step in the study took place in the lab of co-author Dr Keisuke Kaji from the Medical Research Council (MRC) Centre for Regenerative Medicine at the University of Edinburgh. That work is the subject of a separate study in the same issue of the journal.

Kaji told the press that:

"I was very excited when I found stem cell-like cells in my culture dishes. Nobody, including me, thought it was really possible."

"It is a step towards the practical use of reprogrammed cells in medicine," Kaji added.

In 2005 Nagy created Canada's first embryonic stem cell lines from embryos no longer needed by couples undergoing fertility treatment.

The Canadian Stem Cell Network and the Juvenile Diabetes Research Foundation (United States) paid for the research.
www.medicalnewstoday.com/articles/140714.php

Grazie mille, ora è più chiaro!