Reparative osteogenesis in the damaged vertebrae is a complex cascade of morphological and biochemical processes that result in the consolidation of the vertebral body. This research was aimed at studying the features of reparative osteogenesis in damaged thoracic and lumbar vertebral bodies at different time points after injury. We analyzed the morphological findings of the vertebral tissues harvested during surgical interventions in 43 patients with recent, subacute and long-standing injuries to thoracic and lumbar spine, and found that cell differentiation in osteogenesis is closely related to angiogenesis and the metabolic cascade. In areas with sufficient oxygenation, good partial pressure of oxygen, and active growth of microvasculature the normal cycle of development and differentiation of osteoblasts and osteocytes occurs, and hypoxia and acidosis lead to pathological osteogenesis. The reclination maneuver with dorsal tools on Day 10-12 of the injury may be ineffective due to the formation of adhesions between fragments, and reclination of the body of the damaged vertebra two weeks or more after the injury is apparently doomed to failure. Timely ventral fusion performed for objective indications is the key to successful rehabilitation of patients, on the one hand, and reduction of the surgical trauma volume in the future, on the other.

It is not understood how the numbers and identities of vertebrae are controlled during mammalian development. The remarkable robustness and conservation of segmental numbers may suggest a digital nature of the underlying process. Here I propose a mechanism that allows cells to obtain and store the segmental information in digital form, and to produce a pattern of chromatin accessibility that in turn regulates Hox gene expression specific to the metameric segment. The model requires that a regulatory element be present such that the number of occurrences of the motif between two consecutive Hox genes equals the number of segments under the control of the anterior gene. This is true for the recently discovered HRC3 motif, associated with histone modifications and developmental genes. The finding not only allows correctly predicting the numbers of segments using only sequence information, but also resolves the 40-year-old enigma of the function of temporal and spatial collinearity of Hox genes. The logic of the mechanism is illustrated in an animated video: https://youtu.be/4a3XOQ7Lz28. I also discuss how different aspects of the proposed mechanism can be tested experimentally.

Eight amniote genera (representing four clades) became aquatic during the Permian. The four clades were mesosaurids, tangasaurids, the neodiapsid Claudiosaurus, and the procolophonid Barasaurus. Two of eight genera survived the end-Permian mass extinction, but did not last long into the Mesozoic. A previously undescribed specimen of Claudiosaurus germaini, preserved in a lacustrine concretion from the Sakamena Formation, Madagascar, bears seventeen vertebrae that has been split along an approximate horizontal plane to reveal sections of neural canal casted in white calcite. Enlargement of the neural canal in the sacral region of this specimen of Claudiosaurus (vertebral segments 22-26) is more similar to that of Tupinambis (segments 24-28) than it is to Testudo (segments 16-23). Claudiosaurus skeletal anatomy provides evidence for swim propulsion by both hind limbs and by undulation of a dorsal-ventrally flattened tail. Evidence for the latter includes elongate transverse processes on distal tail vertebrae. Other Permian aquatic reptile genera (Mesosaurus, Hovasaurus, Barasaurus) used snake-like side-to-side tail undulation, whereas Claudiosaurus used cetacean-like up-down tail undulation in the vertical plane. It seems unlikely that any of these animals were particularly fast swimmers.