Ueharu, H. | bioRxiv Science

bioRxiv2026

X chromosome inactivation as a novel mechanism for chondrogenesis

X chromosome inactivation (X-inactivation) is generally regarded as a dosage-compensation mechanism restricted to female mammals. Here we show that BMP signaling induces X-inactivation through upregulation of Xist and promotes chondrogenesis in both sexes. Remarkably, augmented BMP signaling induced ectopic X-inactivation: transiently inactivating both X chromosomes in females and one in males in a tissue-specific manner. In cranial neural crest cells, ectopic X-inactivation suppressed X-linked gene Tmsb4x, leading to ectopic cartilage formation. Genetic reduction of Xist or pharmacological restoration of the Tmsb4x product suppressed this phenotype. Moreover, we identified ectopic X-inactivation in SOX9-positive chondroprogenitors during wild-type forelimb development in both sexes. Inhibition of X-inactivation disrupts proximodistal limb patterning ex vivo. These findings establish X-inactivation as a signaling-dependent developmental mechanism linking chromosome-scale gene alterations to skeletal fate specification.

Developmental Biology↗

bioRxiv2025

A lipid metabolism defect is an underlying contributor to Diamond Blackfan anemia syndrome

Analysis of neither Diamond Blackfan anemia syndrome (DBAS) cohorts nor animal models has revealed a potential mechanism for the variable anemia phenotype, a key feature of this disease. Here, we utilized an established Rpl5Skax23-Jus/+ murine DBAS model in order to study this dynamic erythropoiesis deficiency. These haploinsufficient mice exhibit variably penetrant craniofacial and cardiac defects mimicking the phenotypes of DBAS patients bearing RPL5 mutations. We additionally discovered that this specific heterozygous splicing mutation is pathogenic and leads to partial intron retention. By examining the transcriptome of fetal liver erythroid progenitors at E12.5, we demonstrate that the downregulation of erythroid differentiation pathways is consistent with the DBAS phenotype. We also identified dysregulated transcription of lipid metabolism genes with significant reduction in the abundance of Scd1 in a subset of E12.5 mutant embryos at risk for erythroid failure. SCD1, a key enzyme that converts saturated to monounsaturated fatty acids, has not been previously linked to erythropoiesis or DBAS. When anemia was induced in adult mice, pretreatment with an SCD1 inhibitor resulted in improved erythropoiesis. This analysis suggests a key role of lipid metabolism in the variable anemia penetrance in DBAS and highlights a previously unappreciated pathway that may serve as a potential target for drug development. Key PointsO_LIThe variable anemia in Rpl5Skax23-Jus/+mice is triggered by intrinsic/extrinsic stress C_LIO_LIRpl5 haploinsufficient murine and human erythroid progenitors exhibit a lipid metabolism signature with downregulation of Scd1/SCD. C_LI

developmental biology↗