Rome Mayor Gianni Alemanno, who announced her death in a statement, called it a great loss "for all of humanity." He praised her as someone who represented "civic conscience, culture and the spirit of research of our time."
Italy's so-called "Lady of the Cells," a Jew who lived through anti-Semitic discrimination and the Nazi invasion, became one of her country's leading scientists and shared the Nobel medicine prize in 1986 with American biochemist Stanley Cohen for their groundbreaking research carried out in the United States.
Her research increased the understanding of many conditions, including tumors, developmental malformations, and senile dementia.
Italy honored Levi-Montalcini in 2001 by making her a senator-for-life.
A petite woman with upswept white hair, she kept an intensive work schedule well into old age. "At 100, I have a mind that is superior - thanks to experience - than when I was 20," she said in 2009.
Levi-Montalcini was born April 22, 1909, to a Jewish family in the northern city of Turin. At age 20 she overcame her father's objections that women should not study and obtained a degree in medicine and surgery from Turin University in 1936.
She studied under top anatomist Giuseppe Levi, whom she often credited for her own success and for that of two fellow students and close friends, Salvador Luria and Renato Dulbecco, who also became separate Nobel Prize winners. Levi and Levi-Montalcini were not related.
After graduating, Levi-Montalcini began working as a research assistant in neurobiology but lost her job in 1938 when Italy's Fascist regime passed laws barring Jews from universities and major professions.
Her family decided to stay in Italy and, as World War II neared, Levi-Montalcini created a makeshift lab in her bedroom where she began studying the development of chicken embryos, which would later lead to her major discovery of mechanisms that regulate growth of cells and organs.
With eggs becoming a rarity due to the war, the young scientist biked around the countryside to buy them from farmers. She was soon joined in her secret research by Levi, her university mentor, who was also Jewish and who became her assistant.
The 1943 German invasion of Italy forced the Levi-Montalcini family to flee to Florence and live underground. After the Allies liberated the city, she worked as a doctor at a center for refugees.
In 1947 Levi-Montalcini was invited to the United States, where she remained for more than 20 years, which she called "the happiest and most productive" of her life. She held dual Italian-U.S. citizenship.
During her research at Washington University in St. Louis, Missouri, she discovered nerve growth factor, or NGF, the first substance known to regulate the growth of cells.
She showed that when tumors from mice were transplanted to chicken embryos they induced rapid growth of the embryonic nervous system. She concluded that the tumor released a nerve growth-promoting factor that affected certain types of cells.
The research increased the understanding of many conditions, including tumors, developmental malformations, and senile dementia. It also led to the discovery by Stanley Cohen of another substance, epidermal growth factor, which stimulates the proliferation of epithelial cells.
The two shared the Nobel Prize for medicine in 1986.
Levi-Montalcini returned to Italy to become the director of the laboratory of cell biology of the National Council of Scientific Research in Rome in 1969.
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