Scientists are one step closer to understanding how human ovaries develop a lifelong supply of egg cells known as ovarian reserves.
A new study published August 26 in the journal Nature Communications mapped the emergence and progression of cells and molecules developing in monkey ovarian reserves from the early stages of embryonic ovarian development to six months after birth.
The map fills some of the gaps in “really important fields of biology that are truly important” by Amander Clark, a research co-author who is a developmental biologist at UCLA.
Researchers can use the map to build better models of lab ovaries to study reproductive diseases associated with ovarian reserves, she said.
Mystical Development
The ovaries are the main female reproductive organs and play two important roles in female health and reproduction. Egg cell production. It produces sex hormones such as estrogen, progesterone, and testosterone.
The ovaries begin to develop first in the embryo about 6 weeks after fertilization. In the early stages, germ cells that develop into egg cells divide and connect with each other in complex chains called nests. When these nests rupture, individual egg cells are released and enveloped in a special layer of cells called pre-granula cells.
Surrounded by pre-granular sac cells, these eggs are called primordial follicles and constitute ovarian sanctuaries.
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The primitive follicles begin to form about 20 weeks after fertilization and collect at the medial margin of the ovary. When the follicles closest to the ovary center of these clusters mature, they grow and produce sex hormones.
Therefore, it is the primitive follicles that ensure that the ovaries produce mature eggs and do their job of releasing hormones, Clark said.
Multiple ovarian diseases and conditions are rooted in cellular issues in ovarian reserves. For example, the exact cause of PCOS is still unknown, but primitive follicles include dysfunction. Still, little work has been done to understand their development.
Building a map of how, when, and how ovarian reserves are formed during pregnancy can help you understand why certain diseases and fertility issues arise over a lifetime. “That’s what started this research,” Clark said.
Related: The first “atlas” in human ovaries could lead to a breakthrough in fertility, scientists say
Surprising survey results
To investigate how ovarian reserves originate from primates, Clark and her team saw a species of monkey physiologically similar to humans. This will be a proper substitute for what happens developmentally in humans, she said.
First, female monkey embryos and fetuses were collected at various stages of development and ovarian tissue samples were collected. The researchers focused on several important time points: day 34 (when the genital organs become either male or female), 41 (early ovarian growth), 50-52 (end of embryonic stage), 100 (when the egg nest expands), 130 (when the nest ruptures and primitive follicles form).
The team then analyzed the location and molecular fingerprints of ovarian cells to understand important events in the formation of ovarian reserves.
They found that pre-granula cells were formed in two waves, but only during the second wave 41 to 52 days ago it was possible for young eggs to form primitive follicles.
They also identified two genes that appear to be active prior to this second wave. Researchers said further looking at the function of these genes could help identify the developmental origins of ovarian reserve problems.
Clark also said he was totally surprised to learn that the team would “pass through the practice round of hair follicle formation before birth.” This means that as soon as the ovarian reserve is created, some of the more centrally located follicles can mature and produce hormones. Researchers suggest that determining why these follicles are usually activated can provide insight into the causes of PCOS.
Still, researchers are looking at a very dynamic period when embryo cell composition can change dramatically. And they have a large time gap between observation periods.
“This stage, when cell lines are designated, is very dynamic and cell composition changes within a few days,” Garcia Alonso said. So, she added, teams need to collect more tiny data at more points to get a better grasp of what’s going on.
This article is for informational purposes only and is not intended to provide medical advice.
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