Development of the lamprey velum and implications for the evolution of the vertebrate jaw

Background The vertebrate jaw is thought to have evolved through developmental modification of the mandibular arch. An extant jawless vertebrate, the lamprey, possesses a structure called velum-a mandibular arch derivative-in addition to the oral apparatus. This leads us to assess the velum's possible contribution to the evolution of jaws. Results The velar muscles develop from progenitor cells distinct from those from which the oral muscles develop. In addition, the oral and velar regions originate from the different sub-population of the trigeminal neural crest cells (NCCs): the former region receives NCCs from the midbrain, whereas the latter region receives NCCs from the anterior hindbrain. The expression of patterning genes (eg,DlxAandMsxA) is activated at a later developmental stage in the velum compared to the oral region,and more importantly, in different cells from those in the oral region. Conclusion The lamprey mandibular arch consists of two developmental units: the anterior oral unit and the posterior velar unit. Because structural elements of the lamprey velum may be homologous to the jaw, the evolution of vertebrate jaws may have occurred by the velum being released from its functional roles in feeding or respiration in jawless vertebrates.

Automated summary

The vertebrate jaw is believed to have evolved through modification of the mandibular arch. The lamprey, a jawless vertebrate, has a structure called velum derived from the mandibular arch. The velum's contribution to jaw evolution may involve distinct development pathways from oral muscles and neural crest cell origins.