Traditionally, RNA methylation has been studied in the context of gene expression regulation, RNA stability and translation efficiency, with its primary role thought to be in modulating cellular homeostasis and protein synthesis. However, a 2025 study by Dharmadkikari and colleagues uncovers an unexpected and critical function for RNA methylation in mitotic spindle integrity.

The study identifies a critical role for SPOUT1/CENP-32-dependent methylation in mitotic spindle formation and accurate chromosome segregation. Originally identified in a large-scale analysis of proteins associated with mitotic chromosomes, SPOUT1/CENP-32 encodes a putative RNA methyltransferase. The protein localizes to mitotic spindles, and when it is absent centrosome detachment from the spindle poles, delayed anaphase, and chromosome segregation errors are observed. Further, CRISPR experiments in human cells show that the protein is essential for cell viability.

Newly Characterized Neurodevelopmental Disorder

The researchers identified 28 individuals from 21 families harboring biallelic variants in the SPOUT1/CENP-32 gene through exome and genome sequencing. The affected individuals exhibited microcephaly, intellectual disability, developmental delays and seizures. This allowed the researchers to identify a previously uncharacterized autosomal recessive neurodevelopmental disorder termed SpADMiSS (SPOUT1-Associated Development Delay, Microcephaly, Seizures, Short Stature), and expands the known spectrum of centrosome-associated diseases, previously linked to genes like CDK5RAP2, PCNT, WDR62, and ASPM.

To explore the functional role of SPOUT1/CENP-32, the study employed zebrafish models, demonstrating that spout1/cenp-32 mutants had smaller head sizes and increased apoptosis, consistent with the observed human pathology. Complementation assays in zebrafish confirmed that human disease-associated variants disrupted the protein’s function.

The Role of SPOUT/CENP-32

Structural analyses revealed that most pathogenic mutations affect the catalytic domain of SPOUT1/CENP-32, reducing its methyltransferase activity in vitro. Using the MTase-Glo™ Methyltransferase Assay researchers confirmed enzyme dysfunction in mutant variants, reinforcing that RNA methylation is crucial for centrosome function and mitotic spindle stability.

Further, cellular experiments using siRNA depletion in human cells demonstrated that SPOUT1/CENP-32 is essential for proper centrosome-spindle pole attachment. Pathogenic variants resulted in chromosome misalignment, increased apoptosis, and cell cycle arrest.

The study demonstrates that SPOUT1/CENP-32 is an active RNA methyltransferase that modifies RNA to regulate centrosome function. This is a groundbreaking discovery, as it highlights that RNA modifications are critical for proper mitotic spindle organization.

Implications for Understanding Neurodevelopmental Diseases

The findings demonstrate that SPOUT1/CENP-32 variants associated with SpADMiSS reduce methyltransferase activity, leading to defective centrosome tethering and increased chromosome segregation errors. The disruption of this process results in delayed cell cycle progression, increased apoptosis, and severe neurodevelopmental defects, highlighting a novel and essential function for RNA modifications beyond their well-established roles in post-transcriptional regulation. This paradigm shift expands our understanding of RNA epigenetics in cell division, suggesting that RNA methylation could be a key regulatory mechanism in mitotic fidelity and developmental brain disorders, perhaps presenting a viable target for therapeutic drug research and development.

The video animation above shows normal duplication of the centrioles, formation of mitotic spindle and segregation of the chromosomes to the poles before anaphase. With SPOUT1/CENP-32 mutations, the mitotic spindle prematurely detaches from the poles and onset into anaphase is delayed, often with chromosome segregation errors.

Read the paper:

Dharmadhikari AV, Abad MA, Khan S, et al. (2025) RNA methyltransferase SPOUT1/CENP-32 links mitotic spindle organization with the neurodevelopmental disorder SpADMiSS. Nat Commun. 16:1703. DOI: 10.1038/s41467-025-56876-w​.

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Michele Arduengo

Supervisor, Digital Marketing Program Group at Promega Corporation

Michele earned her B.A. in biology at Wesleyan College in Macon, GA, and her PhD through the BCDB Program at Emory University in Atlanta, GA where she studied cell differentiation in the model system C. elegans. She taught on the faculty of Morningside University in Sioux City, IA, and continues to mentor science writers and teachers through volunteer activities. Michele manages the digital marketing program team at Promega.

Latest posts by Michele Arduengo (see all)

• An Unexpected Role for RNA Methylation in Mitosis Leads to New Understanding of Neurodevelopmental Disorders - March 27, 2025
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• Exploring the Respiratory Virus Landscape: Pre-Pandemic Data and Pandemic Preparedness - October 29, 2024