Poche, R. A. | bioRxiv Science

bioRxiv2024

Morphogenic, molecular, and cellular adaptations for unidirectional airflow in the chicken lung

Unidirectional airflow in the avian lung enables gas exchange during both inhalation and exhalation. The underlying developmental process and how it deviates from that of the bidirectional mammalian lung are poorly understood. Sampling key developmental stages with multiscale 3D imaging and single-cell transcriptomics, we delineate morphogenic, molecular, and cellular features that accommodate the unidirectional airflow in the chicken lung. Primary termini of hyper-elongated branches are eliminated via proximal-short and distal-long fusions, forming parabronchi. Neoform termini extend radially through parabronchial smooth muscle to form gas-exchanging alveoli. Supporting this radial alveologenesis, branch stalks halt their proximalization, defined by SOX9-SOX2 transition, and become SOX9low parabronchi. Primary and secondary vascular plexi interface with primary and neoform termini, respectively. Single-cell and Stereo-seq spatial transcriptomics reveal a third, chicken-specific alveolar cell type expressing KRT14, hereby named luminal cells. Luminal, alveolar type 2, and alveolar type 1 cells sequentially occupy concentric zones radiating from the parabronchial lumen. Our study explores the evolutionary space of lung diversification and lays the foundation for functional analysis of species-specific genetic determinants.

developmental biology↗

bioRxiv2021

FOXO1 represses Sprouty2 and Sprouty4 expressionin endothelial cells to promote arterial specification and vascular remodeling in the mouse yolk sac

The establishment of a functional circulatory system is required for post-implantation development during murine embryogenesis. Previous studies in loss of function mouse models have shown that FOXO1, a Forkhead family transcription factor, is required for yolk sac vascular remodeling and survival beyond embryonic day (E) 11. Here, we demonstrate that loss of FoxO1 in E8.25 endothelial cells results in increased Sprouty2 and Sprouty4 transcripts, reduced expression of arterial genes, and decreased Flk1/Vegfr2 mRNA levels without affecting overall endothelial cell identity, survival, or proliferation. Using a Dll4-BAC-nlacZ reporter line, we found that one of the earliest expressed arterial genes, Delta like 4 (Dll4), is significantly reduced in the yolk sac of FoxO1 mutants without being substantially affected in the embryo proper. We show that in the yolk sac, FOXO1 not only binds directly to a subset of previously identified Sprouty2 gene regulatory elements (GREs), as well as newly identified, evolutionarily conserved Sprouty4 GREs, but can also repress their expression. Additionally, over expression of Sprouty4 in transient transgenic embryos largely recapitulates reduced expression of arterial genes seen in endothelial FoxO1 mutant mouse embryos. Together, these data reveal a novel role for FOXO1 as a key early transcriptional repressor controlling both pre-flow arterial specification and subsequent vessel remodeling within the murine yolk sac.

developmental biology↗