# Single nuclei and spatial profiling of sacrococcygeal teratomas reveals cellular composition and X inactivation heterogeneity

## TL;DR

This study uses single nuclei RNA-seq and spatial transcriptomics to explore the cellular makeup and X inactivation patterns in sacrococcygeal teratomas, revealing insights into their heterogeneity and sex bias.

## Contribution

The study reveals X inactivation heterogeneity in female sacrococcygeal teratomas and links it to cellular identity and sex bias.

## Key findings

- Five broad cellular lineages were identified in sacrococcygeal teratomas.
- A subset of female tumor cells showed biallelic X-linked gene expression.
- Biallelic X-chromosome activation may contribute to the sex bias of sacrococcygeal teratomas.

## Abstract

Sacrococcygeal teratomas (SCTs) are the most common neonatal tumors, yet their cellular origins, clinical stratification, and sex bias–occurring three times more in XX than XY individuals—remain poorly understood. To address these gaps, we examined six postnatal (one male and five female) and two prenatal (both female) SCTs by single nuclei RNA-seq and spatial transcriptomics. We identified five broad cellular lineages in SCTs: stroma, epithelia, endothelia, neuroectoderm, and immune. The transcriptomes and lineage compositions showed significant heterogeneity, which offer a framework for future molecular stratification. SCTs are thought to originate from and be propagated by pluripotent cells, notably however, we did not detect these populations. Among female tumors, a subset of cells exhibited biallelic expression of X-linked genes, consistent with X-inactivation failure or reactivation of the once inactivated X-chromosome. These biallelic cells were enriched for developmental and neuronal programs, whereas cells with single-allelic X-chromosome preferentially expressed immune-related genes. Biallelic X-chromosome activation, which can occur only in female cells, may result in transcriptomic features that favor survival of tumor cells, contributing to the sex bias of SCTs. Our findings reveal a link between X-chromosome inactivation and SCT cell identity, suggesting that X-dosage dysregulation may influence SCT heterogeneity and immune landscape.