Plasma prolactin axis shift from placental to pituitary origin in late prepartum mice.

The placenta secretes a prolactin (PRL)-like hormone PRL3B1 (placental lactogen II), a luteotropic hormone essential for maintaining pregnancy until labor in mice. A report from 1984 examined the secretion pattern of PRL3B1 in prepartum mice. In the current study, we found contradictory findings in the secretion pattern that invalidate the previous report. By measuring maternal plasma PRL3B1 and PRL every 4 hrs from gestational day 17 (G17), we newly discovered that maternal plasma PRL3B1 levels decrease rapidly in prepartum C57BL/6 mice. Interestingly, the onset of this decline coincided with the PRL surge at G18, demonstrating a plasma prolactin axis shift from placental to pituitary origin. We also found that maternal plasma progesterone regression precedes the onset of the PRL shift. The level of Prl3b1 mRNA was determined by RT-qPCR in the placenta and remained stable until parturition, implying that PRL3B1 peptide production or secretion was suppressed. We hypothesized that production of the PRL family, the 25 paralogous PRL proteins exclusively expressed in mice placenta, would decrease alongside PRL3B1 during this period. To investigate this hypothesis and to seek proteomic changes, we performed a shotgun proteome analysis of the placental tissue using data-independent acquisition mass spectrometry (DIA-MS). Up to 5,891 proteins were identified, including 17 PRL family members. Relative quantitative analysis between embryonic day 17 (E17) and E18 placentas showed no significant difference in the expression of PRL3B1 and most PRL family members except PRL7C1. These results suggest that PRL3B1 secretion from the placenta is suppressed at G18 (E18).

Receptor Tyrosine Kinase EPHA2 Drives Epidermal Differentiation through Regulation of EGFR Signaling.

Intricate signaling systems are required to maintain homeostasis and promote differentiation in the epidermis. Receptor tyrosine kinases are central in orchestrating these systems in epidermal keratinocytes. In particular, EPHA2 and EGFR transduce distinct signals to dictate keratinocyte fate, yet how these cell communication networks are integrated has not been investigated. Our work shows that loss of EPHA2 impairs keratinocyte stratification, differentiation, and barrier function. To determine the mechanism of this dysfunction, we drew from our proteomics data of potential EPHA2 interacting proteins. We identified EGFR as a high-ranking EPHA2 interactor and subsequently validated this interaction. We found that when EPHA2 is reduced, EGFR activation and downstream signaling are intensified and sustained. Evidence indicates that prolonged SRC association contributes to the increase in EGFR signaling. We show that hyperactive EGFR signaling underlies the differentiation defect caused by EPHA2 knockdown because EGFR inhibition restores differentiation in EPHA2-deficient 3-dimensional skin organoids. Our data implicate a mechanism whereby EPHA2 restrains EGFR signaling, allowing for fine tuning in the processes of terminal differentiation and barrier formation. Taken together, we purport that crosstalk between receptor tyrosine kinases EPHA2 and EGFR is critical for epidermal differentiation.