The in ovo injection of methionine improves intestinal cell proliferation and differentiation in chick embryos by activating the JAK2/STAT3 signaling pathway

The intestinal health of chick embryos is vital for their life-long growth, and exogenous nutrition intervention may provide sufficient nutrition for embryonic development. In the present study, we investigated the effect of in ovo injection of L-methionine (L-Met) on the intestinal structure and barrier function of chick embryos. There were 4 groups of treatments: the control (CON) group injected with phosphate-buffered saline (PBS) and the other 3 groups injected with 5, 10, and 20 mg L-Met/egg, respectively. The injection was performed on embryonic day 9 (E9), and intestinal samples were collected on the day of hatching for analysis. The results showed that, compared with the CON group, the groups administered an in ovo injection of L-Met increased relative weights of the duodenum, jejunum, and ileum (P < 0.05). Hematoxylin and eosin (H&E) staining showed that the groups injected with 5, 10, and 20 mg L-Met significantly increased villus height and crypt depth (P < 0.05). Moreover, in ovo injection of 10 mg L-Met also increased the transepithelial electrical resistance (TEER) of the jejunum (P < 0.05). Injection with 10 and 20 mg L-Met increased the expression of the tight junction proteins (ZO-1 and claudin-1) and the fluorescence signal intensity of Ki67 and villin proteins (P < 0.05). Further, the protein expression of phospho-Janus kinase 2 (p-JAK2) and phospho-signal transducer and activator of transcription 3 (p-STAT3) was significantly increased by 10 or 20 mg L-Met injection (P < 0.05). In conclusion, the injection of L-Met, especially at a dose of 10 mg, showed beneficial effects on the intestinal integrity of chick embryos due to the activation of the JAK2/STAT3 signaling pathway. Our results may provide new insights for regulating the intestinal development of embryonic chicks and the rapid growth of chicks after hatching.