Three signals nudge a human gonad into being—mapped across 33 cell types
What sets the adrenal gland, kidneys and gonads on their distinct paths while they’re forming side by side—and how do they keep in step as they go? This study asked, concretely: which cells are where, who is talking to whom, and what signals steer fate as the human urogenital system takes shape.
The work, published in Science and led by Guo Jingtao and Wang Xiaoyan at the Institute of Zoology of the Chinese Academy of Sciences, set out to map development in place—so the conversations between neighboring tissues aren’t lost when cells are pulled apart.
How they actually did it
The team combined high-resolution spatial transcriptomics with single‑cell multi‑omics, tissue protein imaging and human embryonic stem cell models. In plainer terms: they measured which genes were active in precise spots across embryonic tissues, linked those gene-activity readouts to single‑cell identities and chromatin states, and then tested specific signal combinations in a dish using stem‑cell‑derived intermediate mesoderm. The analysis resolved major renal, adrenal, gonadal, mesenchymal and neural populations and further classified the dataset into 33 cell types.
Signals that nudge a gonad into being
At Carnegie stage 15 (CS15), spatial cell‑communication analysis showed the nascent gonad receives WNT, BMP and NCAM signals from nearby tissues. Guided by that map, the team treated human embryonic stem cell–derived intermediate mesoderm with BMP7, NCAM1 and CHIR99021—the three‑factor stand‑ins for those cues. In response, early gonadal marker expression increased and the overall transcriptome shifted toward an in vivo early gonadal state. In other words, the combination didn’t just flip a single switch; it pushed the whole profile closer to what’s seen in an embryo.
Tracing a hard‑to‑see structure: rete cells
The study identified PAX8‑expressing rete cells in the region where the rete testis or rete ovarii forms. Naming a marker matters: PAX8 gives researchers a handle to follow these cells’ identity and potential contributions as the urogenital tract connects up.
Two adrenal fetal‑zone programs, one male gonadal timeline
On the hormone‑making front, researchers distinguished three steroidogenic populations and highlighted two adrenal fetal‑zone states. FZ_state I showed a stronger de novo cholesterol‑synthesis program marked by SREBF2. FZ_state II expressed the lipoprotein receptors SCARB1 and LDLR together with cortisol‑synthesis genes. Meanwhile, male gonadal steroidogenic cells differentiate after CS19 during embryogenesis and express androgen biosynthetic genes.
Put together, the findings describe human urogenital development as a coordinated multiorgan process: local cell‑to‑cell signals tune early fates, and later steroidogenic programs across adrenal and gonad align with sex differentiation.
The deeper cut
Why SREBF2 vs SCARB1/LDLR is a telling split
Steroidogenic cells need cholesterol as feedstock. There are only two routes to get it: make it from acetyl‑CoA (de novo biosynthesis) or import it on lipoprotein particles. SREBF2 is the master transcriptional regulator of the biosynthetic arm; when its targets are up, flux through HMG‑CoA synthase/reductase and downstream enzymes rises. SCARB1 and LDLR, by contrast, gate uptake—high expression biases the cell toward extracting cholesterol esters carried on HDL (SCARB1) or ApoB‑containing particles (LDLR). Seeing FZ_state I marked by SREBF2 and FZ_state II by SCARB1/LDLR plus cortisol‑pathway genes is a compact readout of two operating modes in the adrenal fetal zone. It also frames a constraint: steroid output scales with the slower of two processes, cholesterol supply and enzymatic conversion. A state leaning on de novo synthesis may be limited by NADPH supply and mevalonate‑pathway capacity; a state leaning on uptake is limited by extracellular lipoprotein availability and receptor‑mediated endocytosis or selective uptake. That division of labor, captured transcriptionally, helps explain how adjacent steroidogenic populations can differ in both substrate sourcing and hormonal products without moving to a new neighborhood.
| Aspect | What the study reports |
|---|---|
| Who and where | Led by Guo Jingtao and Wang Xiaoyan, Institute of Zoology, Chinese Academy of Sciences; published in Science |
| Core methods | High‑resolution spatial transcriptomics; single‑cell multi‑omics; tissue protein imaging; human embryonic stem cell models |
| Cell‑type resolution | Dataset classified into 33 cell types |
| Early signals (CS15) | Gonadal primordium receives WNT, BMP and NCAM signals |
| In vitro test | BMP7 + NCAM1 + CHIR99021 increased early gonadal markers and shifted the transcriptome toward an in vivo early gonadal state |
| Rete cell marker | Identification of PAX8‑expressing rete cells |
| Adrenal fetal‑zone states | FZ_state I: stronger de novo cholesterol synthesis marked by SREBF2; FZ_state II: SCARB1 and LDLR plus cortisol‑synthesis genes |
| Male steroidogenesis timing | Male gonadal steroidogenic cells differentiate after CS19 |
What the numbers mean—and why they matter
“33 cell types” is not trivia; it’s the granularity at which developmental paths and cross‑talk can be separated. The CS15 signal map ties three named pathways—WNT, BMP, NCAM—to a specific receiving tissue. The in‑dish three‑factor test then shows those cues move a cell population’s entire gene‑expression profile toward an early gonadal identity, not just a lone marker. And timing matters: placing male steroidogenic differentiation after CS19 anchors when androgen biosynthesis ramps during embryogenesis.
What this does not settle (yet)
The findings describe coordinated development across organs, but they do not by themselves establish how each signal is necessary or sufficient in vivo across the full span of human development. The work identifies PAX8‑expressing rete cells and distinguishes adrenal fetal‑zone states by their transcriptional programs; translating those handles into causal roles will require targeted perturbations and additional validation.
Why this map is useful going forward
By laying out where cells sit and which signals they exchange, the study offers a framework for thinking about congenital anomalies and differences of sex development as breakdowns in spatial coordination. It puts named pathways, markers and timepoints on the table—ingredients other teams can now test, block or boost in models.
The paper: Spatial coordination in the codevelopment of the human urogenital system during organogenesis (Science, 2026)
Sources: Spatial mapping reveals how human urogenital organs codevelop during organogenesis (phys.org)
Images: Cover: ZEISS Microscopy from Germany / Wikimedia Commons (CC BY-SA 2.0)
How this article was made: Everyman Science uses AI tools to structure, format and optimise its articles, and occasionally to produce illustrations where no free photograph exists. The reporting these articles are based on is human-produced and cited above. Spotted an error? Write to [email protected] and we will correct it. — The editors How we work.
Science desk team of Everyman Science, curating and reporting on the day’s most significant developments in research, space exploration, and technology.
