Sclerotomes

Sclerotomes are the ventromedial portions of the somites in the developing embryo and are derived from the paraxial mesoderm. They form the axial skeleton, including the vertebral bodies and much of the vertebral arch, as well as contributing to the base of the skull.

During somite maturation, sclerotome cells migrate medially around the notochord and neural tube. Through a process called resegmentation, the caudal half of one sclerotome fuses with the cranial half of the adjacent sclerotome, producing a single vertebral body. The remaining sclerotomal cells contribute to the vertebral arch, pedicles, laminae, and articular processes. Cells surrounding the intervertebral disc contribute to the annulus fibrosus, while the nucleus pulposus originates from the notochord.

Molecular and developmental regulation involve Sonic hedgehog signaling from the notochord and neural tube, which promotes sclerotome formation. Sclerotome progenitors express transcription factors such as Pax1, Pax9, and Sox9 as they differentiate into cartilage that will later ossify to form vertebral bone.

Clinical relevance includes defects of sclerotome development leading to vertebral segmentation anomalies, such as hemivertebrae and congenital scoliosis. Abnormal sclerotome development can also contribute to spinal malformations when the vertebral arch fails to form or fuse properly, as seen in conditions related to spina bifida.

See also somites, myotome, and dermomyotome for related derivatives and developmental context.