The role of fetal breathing-like movements in lung organogenesis.

In this review the recent findings concerning the role of fetal breathing-like movements (FBMs) on lung organogenesis are discussed. We first review the consequences that the lack of FBMs has on lung organogenesis and then we discuss the possible pathways that may be employed in this process. Specifically, we review the data in support of the notion that FBMs are required for the cell cycle kinetics regulation (i.e., cell proliferation and cell death) via the expression of growth factors, such as platelet derived growth factors (PDGFs) and insulin growth factors (IGFs), and thyroid transcription factor 1 (TTF-1). Moreover, the role of FBMs on biochemical differentiation of Clara cells, type I and type II pneumocytes is reviewed. Interestingly, even though type II pneumocytes are able to synthesize surfactant-associated proteins (SPs), in the complete absence of FBMs, they are unable to compile, store and release the surfactant. Similarly, in spite of the expression of some early differentiation markers, in the absence of FBMs, type I pneumocytes are unable to flatten in order to allow the gas exchange in the lung. In fact, we are currently employing the cDNA microarray analysis in search for the molecules that might be specific for the lacking functions in pneumocytes.