Amniotic Fluid Pressure Effects on Lung Morphogenesis in Gallus gallus

Abstract

Amniotic fluid volume is critical for proper lung development, as too little fluid (oligohydramnios) results in a smaller lung, a condition known as pulmonary hypoplasia. Previous investigations of the mechanisms underlying the effects of amniotic fluid primarily focused on the effects of mechanical forces in lung morphogenesis during late gestation, but it is unclear how the forces from amniotic fluid affect lung morphogenesis during early to mid-gestation. In this study, we changed amniotic fluid pressure through altering amniotic fluid volume in chicken embryos in early development (Hamburger Hamilton stages 23-25 (HH stages 23-25) & HH stages 25-27) to study whether amniotic fluid volume impacts lung morphology, proliferation, and gene expression of morphogens (FGF, BMP, HH, and Hox) and mechanosensors during lung development. We found that increasing amniotic fluid pressure in day 4 chicken embryos (HH stage 23) does not significantly change the size of the lungs, expression of key morphogens, or mechanosensors. However, increasing amniotic fluid pressure in day 5 chicken embryos (HH stage 25) increases the size of the lungs without altering proliferation, suggesting additional pressure results in faster lung growth at later stages possibly through changes in cell shape. In day 5-6 lungs, increased amniotic fluid pressure upregulated signaling components in the Hedgehog (HH) pathway and downregulated those in the bone morphogenetic protein (BMP) pathway, suggesting that changes in pressure affect biological pathways in chicken lung morphogenesis. Our study further establishes the effects of mechanical forces on lung development during early gestation, both on biological pathways and lung morphology.