Landmark Study Unlocks Stem Cell, DNA Secrets to Speed Therapies

In a groundbreaking study led by an eminent molecular biologist at Florida State University, researchers have discovered that as embryonic stem cells turn into different cell types, there are dramatic corresponding changes to the order in which DNA is replicated and reorganized.

The findings bridge a critical knowledge gap for stem cell biologists, enabling them to better understand the enormously complex process by which DNA is repackaged during differentiation -- when embryonic stem cells, jacks of all cellular trades, lose their anything-goes attitude and become masters of specialized functions.

As a result, scientists now are one significant step closer to the central goal of stem cell therapy, which is to successfully convert adult tissue back to an embryo-like state so that it can be used to regenerate or replace damaged tissue. Such therapies hold out hope of treatments or cures for cancer, Parkinson’s disease, multiple sclerosis, spinal cord injuries and a host of other devastating disorders.

Using mouse and human embryonic stem cells, FSU researchers employed advanced imaging techniques and state-of-the-art genomics technology to demonstrate, with unprecedented resolution along long stretches of chromosomes, which sequences are replicated first, and which occur later in the process of differentiation.

“Understanding how replication works during embryonic stem cell differentiation gives us a molecular handle on how information is packaged in different types of cells in manners characteristic to each cell type,” said David M. Gilbert, the study’s principal investigator. “That handle will help us reverse the process in order to engineer different types of cells for use in disease therapies.” Internationally renowned for his body of cutting-edge research on chromosomal structure and reproduction that he began as a doctoral student at Stanford University in the 1980’s, Gilbert joined the FSU faculty and was appointed as the first J. Herbert Taylor Distinguished Professor of Molecular Biology in 2006.

Results from the FSU study, which includes contributions from researchers at three other institutions, are described in a paper published in the October 7, 2008, edition of PLoS (Public Library of Science) Biology, a peer-reviewed journal that showcases biological science research of exceptional significance. So prodigious were the findings that the current paper -- “Global Reorganization of Replication Domains During Embryonic Stem Cell Differentiation” -- is focused solely on results observed in the mouse embryonic stems cells; data on the human cells will be detailed in a future report.

“We know that all the information (DNA) required to take on the identity of any tissue type is present in every cell, because we already can, albeit very inefficiently, create whole animals from adult tissue through cloning,” Gilbert said. “We also can make a kind of artificial embryonic stem cells, called induced pluripotent stem cells, out of many adult cell types, but there are two major hurdles remaining. First, the methods currently used rely on the unnatural retroviral insertion of genes into patients’ cells, and these genes are capable of forming tumors. Second, this method is very inefficient as well because only one in 1,000 cells into which the genes are inserted becomes pluripotent. We must learn how cells lose pluripotency in the first place so we can do a better job of reversing the process without risks to patients.

“The challenge is, adult cells are highly specialized and over the course of their family history over many generations they’ve made decisions to be certain cell types rather than others,” he said. “In doing so, they have tucked away the information they no longer need on how to become other cell types. Hence, all cells contain the same genetic information in their DNA, but during differentiation they package it with proteins into ‘chromatin’ in characteristic ways that define each cell type. The rules that determine how cells package DNA are complicated and have been difficult for scientists to decipher.”

But, Gilbert noted, one time that the cell “shows its cards” is during DNA replication.

“During this process, which was the focus of our FSU research, it’s not just the DNA that replicates,” he said. “All the packaging must be replicated as well in each cell division cycle.”

He explained that embryonic stem cells have many more, smaller “domains” of organization than differentiated cells, and it is during differentiation that they consolidate information.

“In fact, ‘domain consolidation’ is what we call the novel concept we discovered,” he said.

Gilbert likened the concept of domain consolidation to the undeclared or “undifferentiated” college student who then consolidates her literature resources during the course of declaring a major and specialization. “From a student with books on all subjects on all of her bookshelves comes a student who has placed all texts pertaining to her major on the eye-level shelf and moved the distantly-related, potentially distracting texts to the hard-to-reach bottom or top shelves,” he said.

“Now, our challenge as scientists,” said Gilbert, “is to build on what we’ve learned about domain consolidation so that we can efficiently and safely create patient-specific induced pluripotent stem cells or even coax the body’s cells to change their specialization in response to medications.”

Invasive Papaya Pest Discovered in AsiaThanks to efforts by scientists in a Virginia Tech-led program, the papaya mealybug — an emerging threat from India to Indonesia — is being identified and contained.

Attacks by the papaya mealybug are a serious threat. In Indonesia, India, countries in the Caribbean and South America, the Hawaiian Islands, and Florida, papaya means millions of dollars for farmers, middlemen, and processors. In West Java, the scourge has wiped out most of the papaya plantations.

In May, 2008, a team from the Integrated Pest Management Collaborative Research Support Program (IPM CRSP), managed by Virginia Tech’s Office of International Research, Education, and Development, identified papaya mealybug on papaya trees at the Bogor Botanical Gardens in West Java, Indonesia.

It was the first reported occurrence of papaya mealybug in Indonesia and Southeast Asia.

A specialist in mealybug taxonomy at the California Department of Agriculture confirmed the identification as papaya mealybug — an unarmored scale insect found in moist, warm climates.

Two months later, on a trip to Tamil Nadu Agricultural University in Coimbatore, India, Muni Muniappan, director of the IPM CRSP at Virginia Tech, recognized the telltale sticky residue on papayas he saw there as papaya mealybug.

In each case, IPM scientists alerted government authorities and advised them on appropriate actions to take. These discoveries are crucial; the sooner authorities can arrest the spread of the papaya mealybug, the better their chances of saving this lucrative tropical crop.

While papaya is an exotic fruit in the northern hemisphere, papain, a product of papaya, is used in a variety of ways every day, including the production of chewing gum, shampoo, and toothpaste and tooth whiteners; as a meat tenderizer; and in the brewing and textile industries. In many tropical countries, papaya is an important commercial crop and a key component of the daily diet.

The papaya mealybug originated in Mexico, where it developed alongside natural enemies and was first identified in 1992. It wasn’t until it jumped countries and started proliferating in places where it had no natural enemies that it began to pose problems. In 1995, it was discovered on the Caribbean island of St. Martin. By the year 2000, it had spread to 13 countries in the Caribbean, to Florida in the United States, and to three countries each in Central and South America.

The papaya mealybug is a particularly devastating pest because it is polyphagous—it feeds on many things. The insect’s host range includes more than 60 species of plants: cassava, papaya, beans, eggplant, melons, hisbiscus, plumeria, pepper, sweet potato, tomato, citrus, mango, and sour sop.

On papaya plants, the mealybug infests all parts of the young leaves and fruits, mostly along the veins and midrib of the older leaves. Young leaves become crinkly and older leaves turn yellow and dry up. Terminal shoots become bunchy and distorted. Affected trees drop flowers and fruits. To add insult to injury, the mealybug secretes a honeydew-like substance that turns into a thick sooty mold growth, making the fruit inedible and unusable for the production of papain.

The good news is that the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) has developed a biological control program to tackle the pest. Biological control is an integrated pest management tactic that pits natural enemies against pests. APHIS has identified three parasitoids including parasitic wasps that are highly effective at containing the mealybug. These natural enemies are being cultured in a laboratory in Puerto Rico and are offered free to countries that request them.

The IPM CRSP, funded by the U.S. Agency for International Development, is a consortium of integrated pest management scientists working to raise the standard of living in developing countries. The IPM CRSP team that traveled to Indonesia included Robert Hedlund, Cognizant Technical Officer for the USAID-funded program; Muniappan; Clemson University entomology Professors Merle Shepard and Gerry Carner; Clemson economics Professor Mike Hammig; Yulu Xia, assistant director of the NSF Center for IPM at North Carolina State; and Aunu Rauf, professor of entomology at Bogor Agricultural University in Indonesia.

While the challenge of reclaiming the papaya plantations from the papaya mealybug seems daunting, Muniappan is optimistic. “The use of parasitoids has been very effective in Caribbean and Latin American countries, and in Florida, Guam, and Palau,” he said. “But we need to be vigilant.”