Rita Levi-Montalcini, 103, a biologist who conducted underground research in defiance of Fascist persecution and went on to win a Nobel Prize for helping unlock the mysteries of the cell, died at her home in Rome on Sunday.

Rome Mayor Gianni Alemanno, announcing, called it a great loss "for all of humanity." He praised her as someone who represented "civic conscience, culture and the spirit of research."

Italy's so-called Lady of the Cells, who was Jewish and 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.

Italy honored Dr. Levi-Montalcini in 2001 by making her a senator-for-life.

Dr. Levi-Montalcini was born April 22, 1909, in the northern city of Turin. 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 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, she 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.

Italy's premier, Mario Monti, paid tribute to Dr. Levi-Montalcini's "charismatic and tenacious" character and for her lifelong battle to "defend the battles in which she believed."

In 1947 Dr. 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, Mo., she discovered nerve growth factor, the first substance known to regulate the growth 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.

Dr. Levi-Montalcini had no children and never married, fearing such ties would undercut her independence. - AP