Tales from the Mouse Lady
Anne Croy, Professor of Biomedical and Molecular Sciences at Queen’s University, holds a Canada Research Chair (Tier 1) in Reproduction, Development and Sexual Function. She studies animal models to gain insight into what goes wrong during human pregnancy.
The goals of her research are to ensure that every child born is a healthy child and that, for mothers, every pregnancy is complication-free.
How did she choose this path of research? When Croy was growing up, two historic events shaped her future: monkey spaceflights and the development of Salk polio vaccine. Both used nonhuman primates for research and, in both, that research involved veterinarians.
“That’s what motivated me to study veterinary medicine,” she says. “I thought that all veterinarians did research, and I really wanted to get into immunology and vaccine development.”
Convincing the registrar at the Ontario Veterinary College, University of Guelph, of her passion was another matter. Croy had never owned a pet.
“He told me, ‘Why, you didn’t even keep honeybees’,” she recalls. “He thought that I had no experience and no justification, but I had an Ontario scholarship, so they couldn’t turn me away.”
One of three women in a class of 80, she earned a DVM and married a classmate.
“When I got to the end of my veterinary degree, I still wanted to do immunology. I was fortunate to get an opportunity at the Princess Margaret Hospital in Toronto,” she says. It was the late 1960s, and the war on cancer had just begun.
Croy was hired to manage a tricky breeding program for a colony of mice with no thymus – the source of immune cells. Her task was to figure out what was wrong with their immune system.
“That’s how I started my work with immune-deficient mice,” she says.
Twists and turns
Her budding career as a medical researcher came to an standstill, when she and her husband bought a veterinary practice in St. Catherine’s, ON. During this era, she worked on the Ontario licensing board for veterinarians and inspected veterinary schools internationally. She thought she was “done with research.”
Four years later, she had an opportunity to volunteer in Janet Rossant’s research laboratory at Brock University – and grabbed it.
At Brock, while searching for functional immune cells in the mouse uterus, Croy found large, polka dot-filled cells, which she suspected were natural killer cells (NKCs). They were only present during pregnancy.
When mice lacking NKCs were developed as animal models in 1995, Croy obtained histological samples of uterine implantation sites from collaborators at Harvard and in Paris. She immediately noticed differences between normal and NKC-deficient mice.
“When mice don’t have the ability to develop NKCs, they have this very peculiar implantation site. The mouse pups still go to term, but there’s something wrong with the blood vessels.”
Screening those mice strains lead her down a path of research that she continues to walk today.
As part of Croy’s graduate training, she completed a two-week course in mammalian genetics at the Jackson Laboratory in Bar Harbour, Maine. The laboratory is the worldwide repository of all mouse strains. Working there “really convinced me that the mouse is the most effective model for mammalian disease research.”
After graduate school and her research time with Dr. Rossant, Croy took a job, teaching the gross anatomy of cows and horses, at the University of Guelph. She loved her students but found the work much more stimulating when she was asked to incorporate small-animal anatomy. She used regular insights into interesting cases from staff at the Croys’ veterinary practice to direct her veterinary students in innovative ways.
“I was called the ‘Mouse Lady’ at Guelph,” she recalls.
A happy coincidence led to her current research. A friend in Kansas City convinced her to regularly review grant applications submitted to the U.S. National Institutes of Health in the area of perinatology – the study of human pregnancy, birth and infancy. She noted that several researchers had applied to study preeclampsia.
“Since preeclampsia doesn’t happen in livestock, as a veterinarian, I didn’t know much about it,” she says. “I learned that a major pathological finding with preeclampsia is that the mother’s arteries don’t change appropriately for pregnancy at the fetal implantation site.”
Croy realized that she’d seen those abnormal arteries before in her mouse research. The narrow, spiral arteries had “sick” walls – like those that she’d seen in NKC-deficient mice.
Without reviewing the grant applications, “I never would’ve figured out what was happening in those animals,” she says. Realising the potential for using mice as a model for preeclampsia, Croy refocused her research. In 2004, she accepted the Canada Research Chair at Queens University to continue her studies.
NKCs in pregnancy
Her basic research has uncovered much of what we know about the role of NKCs in early pregnancy. This work has helped to shift a paradigm from the belief that the uterus needs to suppress immune cells to prevent fetal rejection to the present view that the activation of lymphocytes in the uterus is necessary for proper fetal development.
“NKCs promote changes that enable the uterus to support a placenta,” she says.
These cells recognize where a fertilized egg implants and kick-start the process of new blood-vessel formation, she says. “That recognition and activation is critical in generating a supply of new blood vessels exactly where the embryo has landed. So, instead of being turned off, these immune cells are turned on, increasing the blood supply to that region of the uterus by 500-fold during pregnancy.”
The NKCs discharge proteins that digest blood vessel walls, altering the smooth muscle cells inside. The vessels expand to roughly four times their original size. Then NKCs slowly release enzymes – the colourful polka dots stored within their cytoplasm. They make a sticky substance that provides a new structure for blood vessel cells, which form small new arteries called capillaries.
“The large, spiral arteries transform from narrow, firm vessels into a wide smear that gets pruned into mature, branching arteries,” she explains.
Croy also studies the role of NKCs in mouse models of diabetic pregnancy. In future, she plans to study the role of NKCs in the formation of new blood vessels in cancer.