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Spinal process shape and vertebral immobility in hominoids and Hox9 mutant mice
Author(s) -
Machnicki Allison L,
Hrycaj Steven M,
Wellik Deneen M,
Reno Philip L
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.578.17
Subject(s) - bipedalism , anatomy , biology , vertebra , sagittal plane , vertebral column , coronal plane , lumbar , shape change , lumbar vertebrae , quadrupedalism , primate , evolutionary biology , neuroscience
The nature of the human/chimpanzee last common ancestor is fundamental for understanding the evolution of human bipedalism. A particular focus is the conformation of its spine. There are multiple mechanisms for stiffening the spine of apes, including reduction of the number of lumbar vertebrae, the level of the transitional vertebra where the articular facets change from coronal to sagittal orientation, and the shape and angulation of the spinous processes. There is debate regarding whether these features are homologous or homoplastic, and thus whether bipedalism evolved from a short stiff back like great apes or a longer lumbar column more similar to monkeys and Miocene hominoids. Genetic modification of Hox9 in mice results in the correlated modification of spinous process shape and placement of the transitional vertebra independent of alternation in lumbar number, mimicking evolutionary changes observed in hominoids. This indicates that the articular facets and spinous processes may be associated developmental modules. To test this hypothesis, we examined this change in spinous process across the thoracolumbar transition in hominoids and compared it to microCT scans of Hox9 modified mice. We used a NextEngine3D scanner to create surface scans of the lower thoracic and lumbar vertebrae of humans, gorillas, chimpanzees, orangutans, and gibbons in order to assess the angulation, orientation, and shape change of the spinous process relative to the position of the transitional vertebra and lumbar number. Humans and gibbons have a similar change in spinous process orientation and shape at the level of the transitional vertebra. Chimpanzees, gorillas, and orangutans each differ in their pattern of spinous process transition across the thoracolumbar boundary suggesting that mechanisms for lumbar stiffening in these taxa may be independently derived. Support or Funding Information This material is based upon work supported by the National Science Foundation under Grant No. DGE1255832, the Wenner Gren Foundation, and by the Pennsylvania State University Hill Fellowship.