Sclerotome

The sclerotome is the ventromedial compartment of a somite, the segmented block of paraxial mesoderm that forms along the developing embryo. It gives rise to the axial skeleton, primarily the cartilage and bone of the vertebral column, and contributes to the surrounding skeletal structures such as the ribs.

Sclerotome development is driven by signaling from the notochord and the floor plate, notably sonic hedgehog. Sclerotome cells migrate medially around the notochord and neural tube, where they condense to form the vertebral bodies (centrum) and the vertebral arches. The ventral portion of the sclerotome contributes to rib cartilage near the developing body wall.

A key feature of sclerotome development is resegmentation. Each sclerotome splits into anterior and posterior halves; the posterior half of one sclerotome fuses with the anterior half of the next to form a single vertebral body. This resegmentation positions spinal nerves to emerge between adjacent vertebrae and aligns them with the direction of limb and trunk innervation, despite nerves exiting at intervals corresponding to original somite levels.

Derivatives also include the annulus fibrosus of intervertebral discs, derived from sclerotome cells surrounding the notochord, while the nucleus pulposus originates from remnants of the notochord. In addition, cranial sclerotomes contribute to portions of the base of the skull. Disruptions in sclerotome formation or segmentation can lead to axial skeletal defects and vertebral segmentation disorders.