Comparative molecular developmental aspects of the mammalian- and the avian lungs, and the insectan tracheal system by branching morphogenesis: recent advances and future directions

"‘Specifically, convergence provides a way to tell features that have important functional significance from features that do not.’ Vogel[1]."The development of the vertebrate lung was a decisive preparatory event for adaptation to air-breathing and successful transition from water to land, momentous occasions in the evolution and diversification of animal life (e.g. [2-4]). Cost-effective acquisition of molecular oxygen (O2) allowed accomplishment of more energetic lifestyles like flight (e.g. [5-7]) which lead to marked adaptive radiation and speciation (e.g. [8,9]). Motley of conserved genes and molecular factors orchestrated proper transformations from simple to complex body forms by programmed organization and arrangement of cells and tissue components (e.g. [10-18]). Physiological processes (e.g. metabolic-, respiratory-, and ionic exchange) occur across two-dimensional (2D) surfaces which are increased by the three-dimensional (3D) assemblage of organs, tissues, and cells. Branched structures are common in nature and biology in particular. In the later, they include the conductive nervous tissue (e.g. axons and their arborisation), vascular system, vertebrate lungs, secretory glands, tubules of the kidney, and the insectan tracheal system (e.g. [19-24]). Mainly formed to secrete and/or transport materials/fluids or conduct/transfer ions and effects like electric activity, e.g., actions potentials in nervous tissue, branched systems comprise of distinctively hierarchically arranged structural parts (segments = domains) which interconnect in a coherent manner. The overall morphology granted by the frequency and the geometry of bifurcation. In tubular branched systems, depending on the type of organ, endothelial- (in the vascular system) or epithelial cells (in all the other organs) line the internal space (cavity/lumen). The similarities amongst the various branched biological structures underscore existence of shared programmed regulatory mechanisms which invo