Expression levels and DNA methylation profiles of the growth gene SHOX in cartilage tissues and chondrocytes.

All attempts to identify male-specific growth genes in humans have failed. This study aimed to clarify why men are taller than women. Microarray-based transcriptome analysis of the cartilage tissues of four adults and chondrocytes of 12 children showed that the median expression levels of SHOX, a growth gene in the pseudoautosomal region (PAR), were higher in male samples than in female samples. Male-dominant SHOX expression was confirmed by quantitative RT-PCR for 36 cartilage samples. Reduced representation bisulfite sequencing of four cartilage samples revealed sex-biased DNA methylation in the SHOX-flanking regions, and pyrosequencing of 22 cartilage samples confirmed male-dominant DNA methylation at the CpG sites in the SHOX upstream region and exon 6a. DNA methylation indexes of these regions were positively correlated with SHOX expression levels. These results, together with prior findings that PAR genes often exhibit male-dominant expression, imply that the relatively low SHOX expression in female cartilage tissues reflects the partial spread of X chromosome inactivation into PAR. Altogether, this study provides the first indication that sex differences in height are ascribed, at least in part, to the sex-dependent epigenetic regulation of SHOX. Our findings deserve further validation.

Relationships between Slc1a5 and Osteoclastogenesis.

Slc1a5 (ASCT2) encodes a small neutral amino-acid exchanger and is the most well-studied glutamine transporter in cancer cells. To investigate the role of Slc1a5 in osteoclastogenesis, we developed Slc1a5-deficient mice by using a conventional gene-targeting approach. The Slc1a5-/- mice showed no obvious abnormalities in growth. Glutamine uptake was assessed in Slc1a5+/+ and Slc1a5-/- bone marrow cells stimulated with RANKL. The rate of glutamine uptake in Slc1a5-/- bone marrow cells was reduced to 70% of that of cells from Slc1a5+/+ bone marrow. To confirm the involvement of Slc1a5 in osteoclast formation, bone marrow cells derived from Slc1a5+/+ or Slc1a5-/- mice were stimulated with RANKL and macrophage colony-stimulating factor and stained with tartrate-resistant acid phosphatase. The bone resorption activity and actin ring formation of stimulated cells were measured. The formation of multinucleated osteoclasts in bone marrow cells isolated from Slc1a5-/- mice was severely impaired compared with those from Slc1a5+/+ mice. RANKL-induced expression of ERK, NFκB, p70S6K, and NFATc1 was suppressed in Slc1a5-/- osteoclasts. These results show that Slc1a5 plays an important role in osteoclast formation.

Identification of epigenetic memory candidates associated with gestational age at birth through analysis of methylome and transcriptional data.

Preterm birth is known to be associated with chronic disease risk in adulthood whereby epigenetic memory may play a mechanistic role in disease susceptibility. Gestational age (GA) is the most important prognostic factor for preterm infants, and numerous DNA methylation alterations associated with GA have been revealed by epigenome-wide association studies. However, in human preterm infants, whether the methylation changes relate to transcription in the fetal state and persist after birth remains to be elucidated. Here, we identified 461 transcripts associated with GA (range 23-41 weeks) and 2093 candidate CpG sites for GA-involved epigenetic memory through analysis of methylome (110 cord blood and 47 postnatal blood) and transcriptional data (55 cord blood). Moreover, we discovered the trends of chromatin state, such as polycomb-binding, among these candidate sites. Fifty-four memory candidate sites showed correlation between methylation and transcription, and the representative corresponding gene was UCN, which encodes urocortin.