Symmetry breaking in biological systems. From molecules to tissues

Chirality of biomolecules is one of the major characteristics of living systems. Molecular asymmetry can be detected in the earliest prokaryotes and stereoselective synthesis of proteins and polysaccharides was recognized since Pasteur’s time. More recently much attention was paid to the molecular origin of asymmetric development of organs. This asymmetry can be followed up to the cellular and tissue levels. We compared the periorbital wrinkle pattern (crow’s feet) around the left and right eyes, as well as the microdepressional skin surface relief on the left and right arms. The pattern of these reliefs was shown to change with age in a typical manner. Apparently this age-dependent modification of the skin surface micro-relief as well as wrinkle formation is largely determined by the progressive modifications of the dermal extracellular matrix (ECM) and especially of the elastic fiber network as the result of the oriented (vectorial) biosynthetic activity of dermal fibroblasts. These cells do not form a homogeneous population as shown by their proliferation pattern. The reaction of these cells to receptor-mediated stimuli—by growth factors, cytokines, and hormones also exhibit microheterogeneity. Cell–cell interactions, especially between the keratinocyte layers of the epidermis and dermal fibroblasts might also play an important role in the regulation of cell-patterning. These mechanisms might well explain the asymmetry detected by our semi-automated image analysis program on left–right microdepressionary skin surface relief, as well as periorbital wrinkle formation.