A single protein on one type of cell controls whether someone can have children
Beneath the familiar story of puberty lies a cellular conversation science is only beginning to hear. Researchers in Spain have discovered that microglia — long understood as the brain's immune sentinels — also guide the hormonal cascade that initiates reproductive development, doing so through a protein called RANK that allows them to physically communicate with the neurons governing sex hormone release. The finding, drawn from mouse studies and confirmed in part through human genetic data, reframes these immune cells as quiet architects of fertility, and raises the possibility that some cases of human infertility trace back to a breakdown in this previously invisible dialogue.
- A protein called RANK, sitting on the surface of microglia, turns out to be essential to reproductive development — its deletion in mice caused infertility, shrunken ovaries, reduced testosterone, and collapsed hormone levels.
- The disruption isn't limited to early life: knocking out RANK at the precise moment puberty begins left roughly half of treated male mice infertile as adults, suggesting microglia's reproductive role persists well beyond development.
- Human genetic data from 564 infertility patients revealed that six carried RANK mutations — a small but significant signal that this mouse-derived mechanism has real consequences in people.
- Without RANK, microglia physically change — shrinking, losing branches, and making fewer contacts with the GnRH neurons they are supposed to support, offering a structural picture of how the breakdown occurs.
- Researchers now face the deeper question of what activates RANK in microglia and what cues them to engage at puberty's threshold — answers that could open new therapeutic paths for reproductive disorders.
For decades, microglia were understood as the brain's immune custodians — scavenging debris, fighting pathogens, maintaining order. A study published this spring in Science reveals they carry a second, hidden responsibility: helping to trigger puberty itself.
The discovery emerged from work at Spain's National Cancer Research Center, where researchers found that microglia in the hypothalamus physically interact with neurons that produce gonadotropin-releasing hormone, or GnRH — the chemical signal that sets the entire reproductive hormone cascade in motion. Central to this interaction is a surface protein called RANK. When scientists deleted the RANK gene in mice, the consequences were swift and severe: sex hormone levels fell, fertility declined, ovaries shrank, testosterone dropped, and the structural hallmarks of reproductive health deteriorated in both sexes.
To sharpen the finding, the team used a cancer drug to eliminate RANK specifically at the onset of puberty. About half of the male mice treated this way became infertile as adults. When microglia were depleted entirely using a separate drug, the same reproductive damage appeared. Under the microscope, microglia lacking RANK looked visibly diminished — smaller, with fewer branching extensions, making less physical contact with the GnRH neurons they are meant to support.
The researchers then turned to human data, analyzing genetic profiles from 564 people with congenital hypogonadotropic hypogonadism, a condition defined by low sex hormones and frequent infertility. Six individuals carried mutations in the RANK gene — one percent of the group, a modest but meaningful signal that the mechanism observed in mice is also at work in some infertile people.
What remains unknown is how RANK itself gets activated, and what cues microglia to engage with GnRH neurons at the precise biological moment puberty should begin. Those answers, researchers say, could eventually point toward new treatments for infertility — but first, science must learn to read a conversation it didn't know was happening.
For decades, neuroscientists have understood microglia as the brain's cleanup crew—cells that scavenge debris and fight off pathogens. A new study published in Science this spring reveals they do something else entirely: they help orchestrate the biological cascade that triggers puberty.
The discovery centers on a small region of the brain called the hypothalamus and a specific type of neuron within it. These neurons produce gonadotropin-releasing hormone, or GnRH, a chemical messenger that signals the pituitary gland to manufacture the sex hormones responsible for ovulation and sperm production. Researchers at Spain's National Cancer Research Center found that microglia cells physically interact with these GnRH neurons and regulate their function—a connection no one had documented before.
The key player in this interaction is a protein called RANK, which sits on the surface of microglia. When researchers deleted the RANK gene in mice, the consequences were immediate and severe. The microglia could no longer communicate effectively with GnRH neurons. Sex hormone levels plummeted. Some animals became infertile. In females, the ovaries shrank and often failed to develop the corpus luteum, a structure essential for pregnancy. Males produced less testosterone and had smaller testes. Both sexes showed unusually low levels of gonadotropins, the hormones that trigger reproductive development.
The team then used a cancer drug called tamoxifen to knock out RANK specifically at the moment puberty began, when mice were four weeks old. About half of the male mice treated this way became infertile as adults, and many showed reduced testicular weight. The findings suggested that microglia's role in reproduction isn't confined to development—it continues to matter throughout life.
To test whether this mechanism exists in humans, the researchers analyzed genetic data from 564 people with congenital hypogonadotropic hypogonadism, a condition marked by low sex hormones and often infertility. Six individuals—one percent of the group—carried mutations in the RANK gene. It was a small number, but it pointed to something real: a cellular mechanism discovered in mice was also broken in some infertile people.
When the team depleted microglia entirely in pubertal mice using a drug called PLX3397, they observed the same reproductive problems: reduced testicular weight in males, fewer corpora lutea in females. Mice engineered to lack RANK only in their microglia showed similar damage, along with reduced expression of GnRH itself. Under the microscope, the microglia without RANK looked different too—smaller, with fewer branches extending from their cell bodies, making fewer physical contacts with the GnRH neurons they're supposed to support.
The implications stretch beyond basic biology. Microglia have been studied intensively for their role in brain development and disease, yet their connection to reproduction has gone unexamined until now. Researchers emphasize that much remains unknown: How does RANK get activated in the first place? What triggers microglia to engage with GnRH neurons at the precise moment puberty should begin? The answers could eventually lead to new treatments for infertility and reproductive disorders, but first, the field must understand the control mechanisms that govern these immune cells' hidden role in making us human.
Notable Quotes
This is a link that hadn't been seen before—the role of microglia in controlling the GnRH neurons— Alejandro Collado-Solé, postdoctoral researcher at Spanish National Cancer Research Center
There's still so much more going on with these immune cells than we think about— Margaret McCarthy, director of the Medicine Institute of Neuroscience Discovery at University of Maryland
The Hearth Conversation Another angle on the story
So microglia are immune cells. Why would they be involved in something as fundamental as puberty?
That's exactly what surprised the researchers. We think of microglia as janitors—they clean up dead cells and fight infection. But they're also wired into nearly every major system in the brain. The hypothalamus is tiny, densely packed, and controls everything from hunger to reproduction. It makes sense that microglia would be there, but nobody had looked at what they were actually doing.
And they found these cells were talking to the neurons that start puberty?
Not just talking—physically touching them, regulating them. The microglia express this protein called RANK, and when you remove it, the whole reproductive system stumbles. Hormone levels drop, fertility collapses. It's a single protein on one type of cell, in one small brain region, and it cascades into something as profound as whether someone can have children.
That seems fragile. What happens if something goes wrong with RANK?
In mice, it's catastrophic. But in humans, it's more subtle. They found that about one in a hundred people with a specific infertility condition carry a broken RANK gene. Not everyone with the mutation is infertile, but the connection is there. It suggests this pathway matters in our species too.
So this could be a new target for treating infertility?
Potentially. But first you have to understand how RANK gets switched on in the first place. Right now, researchers know what happens when it's absent, but not what activates it during normal puberty. That's the next puzzle.
Why did it take so long to find this?
Microglia research is relatively new. And neuroendocrinology—the study of how the brain controls hormones—is old, established, with its own assumptions about how things work. Sometimes the newest tools applied to old questions reveal something nobody thought to look for.