Chemical Tag on mRNA Reveals Hidden Switch That Controls Hair Growth Cycles

A single chemical mark deposited on messenger RNA has emerged as a decisive controller of the hair follicle cycle, according to a new study published in PLOS Genetics. The research, led by Xinyan Gan and Quan Yuan together with colleagues, identifies the enzyme METTL1 as a critical regulator of how hair follicle stem cells commit to their fates and differentiate during the rapid growth phases that produce a mature hair shaft. By manipulating the levels of this enzyme specifically in keratinocytes, the cells that form the bulk of the epidermis and hair follicle, the team showed that removing it causes severe defects in follicle development and regeneration, while boosting it accelerates hair regrowth. The finding adds a surprising new layer to the biology of hair growth, one that operates not at the level of DNA or even of transcription, but on the RNA molecules that carry genetic instructions to the protein-building machinery of the cell.

Hair follicles are among the most dynamic mini-organs in the mammalian body. Each follicle cycles repeatedly through phases of vigorous growth, destruction, and rest, and each new cycle depends on stem cells resident in a region of the follicle called the bulge exiting their quiescent state at precisely the right moment. Once activated, these cells must proliferate, migrate downward, and differentiate into the multiple lineages that construct the follicle and its associated structures. This process demands an extraordinary degree of coordination, and it has long been clear that transcription factors, proteins that switch specific genes on or off, are central to establishing the identity of each cell type. What has remained murky is how cells ensure that the right proteins are actually synthesized in the right amounts once their messenger RNAs have been made, a question of post-transcriptional control that the new study addresses directly.

The answer lies in a chemical modification known as N7-methylguanosine, abbreviated m7G, in which a methyl group is attached to the nitrogen at position seven of a guanosine base. This modification has attracted growing attention in recent years as one of several RNA marks, alongside the better-known m6A modification, that influence the fate and function of RNA molecules inside cells. METTL1, working together with its partner protein WDR4, is the key methyltransferase responsible for installing m7G marks. The modification is best characterized on transfer RNAs, the adaptor molecules of protein synthesis, where it stabilizes the tRNA structure and supports efficient translation. But m7G can also be deposited internally within messenger RNAs, and it is this internal messenger RNA methylation that turned out to be central to the hair follicle story.

To probe the role of METTL1 in hair biology, the researchers created mice in which the Mettl1 gene could be deleted specifically in keratinocytes. The consequences were dramatic. Animals lacking the enzyme in these cells displayed severe dysplasia of hair follicle development, meaning the follicles formed abnormally and failed to achieve their normal architecture. Regeneration was also impaired, with the follicles unable to cycle properly through subsequent rounds of growth. In addition, the team observed disruptions in keratinocyte adhesion, the process by which these cells stick to one another to maintain the structural integrity of the epidermis and follicle. These defects point to METTL1 as a gene whose loss undermines both the construction of the follicle and its ongoing maintenance across cycles.

The complementary experiment strengthened the conclusion. When the researchers introduced a keratinocyte-specific knock-in that increased Mettl1 activity, hair regeneration accelerated. This gain-of-function result demonstrates that the enzyme is not merely permissive for hair growth but is genuinely rate-limiting: more METTL1 means faster regrowth, at least under the conditions of the experiment. Together, the loss-of-function and gain-of-function data establish a bidirectional relationship between METTL1 levels and the tempo of the hair follicle cycle, a relationship that suggests the enzyme could in principle be targeted to modulate hair growth in pathological settings, although the authors are careful to frame the work as mechanistic biology rather than as a therapeutic demonstration.

Mechanistically, the study traced the effects of METTL1 loss to a specific transcription factor with a well-established role in hair biology: HOXC13. This homeobox protein is known to govern the expression of genes required for hair shaft formation and follicle differentiation. The researchers found that when METTL1 is absent, HOXC13 messenger RNA becomes destabilized and its levels fall. The destabilization is attributed to the loss of internal m7G modification on the HOXC13 transcript itself, implying that the methyl mark normally protects or otherwise supports the messenger RNA, allowing it to persist long enough to be translated into protein. Without the mark, the transcript decays, HOXC13 protein levels drop, and the genetic program that depends on HOXC13 falters.

Downstream of HOXC13, the study mapped a signaling axis that connects the RNA modification to the observable defects in the follicle. HOXC13 normally promotes the expression of FOXN1, a transcription factor famous for its role in hair and immune development, and FOXN1 in turn supports the expression of DSG4, a desmoglein, which is a calcium-dependent adhesion molecule of the cadherin family concentrated in the hair shaft and inner root sheath. DSG4 provides the intercellular adhesion that keeps differentiating keratinocytes properly glued together as they build the hair shaft. When METTL1 is lost, HOXC13 messenger RNA decays, FOXN1 declines, and DSG4 falls with it, explaining both the differentiation defects and the adhesion disruptions seen in the knockout animals. The chain from RNA mark to mRNA stability to transcription factor to adhesion molecule constitutes a complete mechanistic pathway linking a chemical modification to tissue architecture.

The conceptual significance of the work extends beyond hair. Biologists have long distinguished between transcriptional regulation, which determines which genes are read into RNA, and post-transcriptional regulation, which determines what happens to those RNA molecules afterward. The new findings show that an RNA modification enzyme can sit upstream of a transcription factor, effectively using post-transcriptional control to tune a transcriptional circuit. In this arrangement, METTL1 does not directly change which genes are transcribed; instead, it safeguards the messenger RNA of a master regulator, ensuring that the transcriptional program for hair differentiation is executed at the right intensity. The authors describe this as an essential regulatory layer of RNA modification in hair follicle morphogenesis and cycling, one that operates through precise post-transcriptional control of a key transcriptional circuit to ensure structural integrity and timely regeneration.

For the broader field of RNA modification biology, the study adds hair follicle cycling to the growing list of developmental and physiological processes controlled by m7G methylation. It also highlights the specificity of the mechanism: although METTL1 modifies many transfer RNAs, the authors found that its effects on hair follicle biology run, at least in part, through internal modification of a single messenger RNA target. This kind of transcript-selective action suggests that m7G marks may function as individualized tuning knobs on particular messages rather than as a blanket adjustment of global protein synthesis, a distinction that will likely shape future experiments in other tissues.

Practical implications remain speculative but tantalizing. Hair loss disorders affect a large fraction of the human population, and most current treatments act indirectly on the follicle cycle. A pathway that demonstrably accelerates regeneration when its enzyme is boosted, and that acts through defined molecular intermediaries, offers a fresh set of potential targets. At the same time, the severe developmental defects caused by METTL1 loss in keratinocytes caution that the pathway is deeply embedded in normal epithelial biology, and any intervention would need to respect its broader roles. For now, the study stands as a vivid demonstration that the fate of a hair, and perhaps of many other tissues, can hinge on a methyl group attached to a single guanosine deep inside a messenger RNA molecule.

Subject of Research: METTL1-mediated m7G RNA modification and its regulation of the hair follicle cycle through the HOXC13/FOXN1/DSG4 axis

Article Title: METTL1-mediated m 7 G modification regulates hair follicle cycle via the HOXC13/FOXN1/DSG4 axis

Article References: Gan, X., Li, Q., Xiong, Q., Huang, D., Liu, Z., Yin, Q., Jiang, S., Matsubara, T., Kokabu, S., Yan, W., & Yuan, Q. (2026). METTL1-mediated m7G modification regulates hair follicle cycle via the HOXC13/FOXN1/DSG4 axis. PLOS Genetics, 22(9), e1012307. https://doi.org/10.1371/journal.pgen.1012307

Image Credits: AI Generated

DOI: 10.1371/journal.pgen.1012307

Keywords: METTL1, m7G modification, RNA methylation, hair follicle cycle, keratinocytes, HOXC13, FOXN1, DSG4, post-transcriptional regulation, hair regeneration, PLOS Genetics, epigenetics