Theca cells are important for female fertility - without them, women cannot make the hormones that support ovarian follicle growth, an essential part of egg production. Now, for the first time, a study finds that theca cells originate from two sources - one inside and the other outside the ovary.
Researchers from the National Institute of Environmental Health Sciences (NIEHS), part of the National Institutes of Health (NIH) and based in Durham, NC, and colleagues report their discovery in the journal Nature Communications.
The finding answers a long-standing question about the origin of one of the cell types that makes up the ovary.
The researchers also discovered how ovarian cells communicate as the ovarian follicle develops.
Ovarian follicles are the heart of the egg-producing part of the female reproductive system - the ovary. They are fluid-filled sacs that hold maturing eggs or oocytes. Follicles develop for each ovulation cycle, but usually only one releases a mature egg, and the others die off.
Senior and corresponding author Dr. Humphrey Yao, a researcher at the NIEHS reproductive and developmental biology laboratory, explains that the ovarian follicle contains the egg surrounded by two distinct cell types - granulosa cells and theca cells.
Theca cells produce the hormone androgen - normally regarded as a male hormone. The granulosa cells convert androgen into the female hormone estrogen.
Theca cells come from both inside and outside the ovary
Dr. Yao says while we know where the egg and granulosa cells come from, the origin of the theca cells, and what directs their development, has been somewhat of a mystery.
The team believes their discovery improves our understanding of basic ovarian biology and how ovarian disorders that lead to hormone imbalances and female infertility arise. Examples of such disorders include premature ovarian failure and polycystic ovarian syndrome.
In their paper, the researchers describe how using mice and a new technique called lineage tracing, they found that in the developing embryo, theca cells come from both inside and outside the ovary.
The cells that come from outside the ovary migrate from the mesonephros, the excretory organ of the embryo.
"We don't know why theca cells have two sources," Dr. Yao explains, "but it tells us something important - a single cell type may actually be made up of different groups of cells."
Theca cells make androgen in response to crosstalk from granulosa and egg cells
The researchers also uncovered the molecular signaling system that enables theca cells to make androgen. The signals arise from crosstalk between the granulosa cells and the immature egg cell or oocyte.
First author Dr. Chang Liu, a visiting fellow in Yao's group, says:
"Now that we know what makes these cells grow, we can search for possible genetic mutations or environmental factors that affect the process leading to ovarian cell disorders."
Dr. Yao also plans to explore the two types of cell that make up theca cells and find out if their discoveries in mice hold up in humans. This may lead to other discoveries about theca cells' role in female fertility, he says.
Meanwhile, in another study that Medical News Today reported recently, scientists at the University of Manchester in the UK describe the mechanism that nourishes the early embryo in the womb.
Writing in the journal Placenta, the team describes how glands in the lining of the uterus store and deliver glycogen to the placenta during early embryo growth. The supply from the glands gradually wanes as the fetus grows big enough to receive blood directly from the mother.