Furthering follicle fortunes

by Amina Ali

ome key factors affecting the growth of ovarian cells before fertilization -- and limiting reproductive technologies for the dairy industry -- are being unlocked by U of G researchers.

Biomedical science professors Jonathan LaMarre and Patricia Gentry are identifying several components of the growth of ovarian follicles -- the small structures in the ovary made up of the egg and surrounding "nursemaid" cells.

"In spite of many recent advances, follicle failure continues to be one of the factors limiting bovine reproductive success," says LaMarre. "Enhancing the reproductive success of cows suited to milk production would accelerate the development of high-producing herds."

Normally, a cow ovulates a single oocyte (egg) once every 28 days. With hormone therapy, the number of oocytes could potentially be increased up to 20 fold. But the potential can't be consistently realized until more is understood about the biology and technology of the process. What restricts the technique is not understood, but LaMarre and Gentry are suggesting some possibilities.

Follicular growth can fail in several ways. In a process known as atresia, several follicles may never make it to their destination, and only one follicle survives. Or the follicle may be "ready to roll," but a follicular cyst prevents its release. Follicular cysts are double trouble -- not only is the follicle prevented from entering the cycle, but a cow is also generally infertile while cysts are present.

LaMarre and Gentry suspect that proteinases -- enzymes regulating the growth of the nursemaid cells surrounding the follicle -- may be prevented from carrying out their job in these disorders. A clotting factor called thrombin is a potent stimulator of growth and hormone production by nursemaid cells. Relative deficiencies in the amount or activity of this enzyme may impair follicular growth and decrease fertility. Because these enzymes work in "cascades," the researchers are also examining the role of other clotting factors and proteins in the control of follicular development.

The follicles used in their studies are collected from cows at slaughter. After the follicular fluid is collected, it is categorized by size and analysed for clotting factor expression. Then the cells are cultured with the specific enzymes to see what effect these factors have on the growth of follicles or individual cells.

"We want a more rapid way to select for traits in our farm animals," says LaMarre. "Enhancing dairy cows' fertility increases profits and leads to a more rapid improvement of genetic quality. Furthermore, these studies help us understand basic aspects of reproductive biology in many species."

This research is sponsored by the Natural Sciences and Engineering Research Council and the Ontario Ministry of Agriculture, Food and Rural Affairs.