How genes establish left-right asymmetry in vertebrate development
Word Count – 1941
While the vertebrate body exhibits bilateral symmetry externally, a remarkable conservation of asymmetry is displayed by the internal organs along the left-right body axis. This asymmetry manifested appears to be conserved in all vertebrates, implying that this asymmetric structure and arrangement of organs is vital and required for their normal function. In fact, asymmetric organ structures are beneficial in many ways. For instance, cardiac left-right asymmetry might more efficient as two separate pumping systems within a single structure are generated which allowed the increased functional complexity associated with the vasculature in vertebrates. Besides, the left-right asymmetries might also help in packing the organ systems, especially the digestive system, efficiently while maintaining the overall size limitations of an organism body cavity. Hence, the normal disposition of organs, called situs solitus, is an essential and distinctive feature of the vertebrate body plan.
Failure to establish a normal organ systems arrangement may result in distinct classes of laterality defects, namely isomerism (failure to achieve left-right asymmetry at the level of individual organs), heterotaxia (one or more of the individual organ systems develops with reserved left-right polarity), and situs inversus (a complete inversion of the global left-right axis). Although situs inversus is not associated with clinically detectable adverse effect, heterotaxia and isomerism are associated with a wide range of cardiopulmonary defects. In various genetic studies, four stages of left-right asymmetrical development were exhibited. The first stage the breaking of symmetry, then followed by the transfer of left-right positional information to the lateral plate mesoderm and stabilization of the side-specific gene expression and lastly the development of the asymmetric organs....