How an egg cell's "operating manual" sets the stage for fertility

October 08, 2020

Baltimore, MD-- Recently published work from Carnegie's Allan Spradling and Wanbao Niu revealed in unprecedented detail the genetic instructions immature egg cells go through step by step as they mature into functionality. Their findings improve our understanding of how ovaries maintain a female's fertility.

The general outline of how immature egg cells are assisted by specific ovarian helper cells starting even before a female is born is well understood. But Spradling and Niu mapped the gene activity of thousands of immature egg cells and helper cells to learn how the stage is set for fertility later in life.

Even before birth, "germ" cells assemble a finite number of cell clusters called follicles in a female's ovaries. Follicles consist of an immature egg cell and some "helper" cells, which guide the egg through its maturation process. It is from a follicle that a mature egg cell bursts during ovulation.

"Follicles are slowly used up during a female's reproductive lifespan and menopause ensues when they run out. Understanding what it takes for follicles to form and develop successfully, helps us learn how damaged genes or adverse environmental factors, including a poor diet, can interfere with fertility," explained Spradling. "By documenting the follicle's genetic operating manual, problems in egg development that might lead to birth defects --as a result of mutations or due to bad nutrition-- can be better understood and reduced."

Spradling and Niu sequenced 52,500 mouse ovarian cells at seven stages of follicle development to determine the relative expression of thousands of genes and to characterize their roles.

The study also illuminated how mammalian ovaries produce two distinct types of follicles and Spradling and Niu were able to identify many differences in gene activity between them.

The first, called wave 1 follicles, are present in the ovary even before puberty. In mice, they generate the first fertile eggs; their function in humans is poorly understood, but they may produce useful hormones. The second type, called wave 2 follicles, are stored in a resting state but small groups are activated to mature during a female's hormonal cycle, ending in ovulation. The findings help clarify each type's roles.

Spradling and Niu's work and all its underlying data were published by Proceedings of the National Academy of Sciences.

"We hope our work will serve as a genetic resource for all researchers who study reproduction and fertility," concluded Spradling.
This work was funded by the Howard Hughes Medical Institute.

Carnegie Institution for Science

Related Fertility Articles from Brightsurf:

What are your chances of having a second IVF baby after fertility treatment for the first?
As the restrictions on fertility clinics start to be lifted and IVF treatment resumes, research published in Human Reproduction journal offers reassuring news to women who have had to delay their treatment for a second IVF baby because of the coronavirus.

Fertility preservation use among transgender adolescents
Transgender adolescents often seek hormonal intervention to achieve a body consistent with their gender identity and those interventions affect reproductive function.

A new way to assess male fertility
Current tests for male fertility include measuring the concentration and motility of spermatozoa.

Male fertility after chemotherapy: New questions raised
Professor Delb├Ęs, who specializes in reproductive toxicology, conducted a pilot study in collaboration with oncologists and fertility specialists from the McGill University Health Centre (MUHC) on a cohort of 13 patients, all survivors of pediatric leukemia and lymphoma.

Vaping may harm fertility in young women
E-cigarette usage may impair fertility and pregnancy outcomes, according to a mouse study published in the Journal of the Endocrine Society.

Are fertility apps useful?
Researchers at EPFL and Stanford have carried out an analysis of the largest datasets from fertility awareness apps.

Marijuana and fertility: Five things to know
For patients who smoke marijuana and their physicians, 'Five things to know about ... marijuana and fertility' provides useful information for people who may want to conceive.

How could a changing climate affect human fertility?
Human adaptation to climate change may include changes in fertility, according to a new study by an international group of researchers.

Migrants face a trade-off between status and fertility
Researchers from the universities of Helsinki, Turku and Missouri as well as the Family Federation of Finland present the first results from a new, extraordinarily comprehensive population-wide dataset that details the lives of over 160,000 World War II evacuees in terms of integration.

Phthalates may impair fertility in female mice
A phthalate found in many plastic and personal care products may decrease fertility in female mice, a new study found.

Read More: Fertility News and Fertility Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to