HE4 (Human Epididymis Protein 4) encoded by the wfdc2 gene was first identified as a highly expressed factor in human epididymis. HE4 expression levels in malignant lesions are correlated with the clinical manifestations of gynecologic cancers. HE4 serum test has been widely used for the triage of patients suspected of gynecologic cancers, prognosis of cancer patients, and monitoring cancer recurrence. While it is reported that HE4 may actively participate in the regulation of cancer cell proliferation, migration and drug sensitivity, the physiological role(s) of HE4 in embryo development remains unknown. We applied the TALEN-based strategy to generate wfdc2 gene deletion mice for observation of HE4 function in organogenesis. While heterozygous mice were normal in terms of birth weight, reproductivity, and general behaviors, all the neonates with homozygous wfdc2 deletion suffered severe dyspnea and died in 10 h after birth. Biopsy detected pale-colored lungs, and mechanistic studies indicated increased apoptosis in type-I alveolar cells in lung tissues, which caused hypovascular lung tissue, then led to severe dyspnea in wfdc2(-/-) neonates. The HE4 knockout mouse has provided an in vivo model for studying the patho-physiological function and relevant molecular pathways of HE4 for the development of respiratory system. (C) 2019 Elsevier Inc. All rights reserved.