ABSTRACT
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 undergo proximal-short and distal-long fusions, forming parabronchi for air conduction. Through the parabronchial smooth muscle, neoform termini extend radially 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.
Footnotes
Author contributions
Formal analysis: K.N.G.-M., G.W., R.N., J.C.; Investigation: K.N.G.-M., L.V.E., G.W., R.N., J.C.; Methodology: K.N.G.-M., P.Y.L., R.A.P., J.C.; Writing – original draft: K.N.G.-M., J.C.; Writing – review & editing: K.N.G.-M., J.C.
Funding
This work was supported by the University of Texas MD Anderson Cancer Center Retention Fund and the National Heart, Lung, and Blood Institute (R01HL130129 and R01HL153511 to J.C.; R00HL155845 to L.V.E.). Deposited in PMC for release after 12 months.
Data and resource availability
E13 and E20 chicken lung scRNA-seq data and E20 chicken lung Stereo-seq data are available at the NCBI Gene Expression Omnibus (GEO) database under accession numbers GSE264623 and GSE274970, respectively. Custom scripts are available at GitHub (https://github.com/chenlab-cchmc/chicken-lung-airflow).
