Alternations of mammary gland morphology, and marker protein expression, related hormones and signaling pathways of mammary gland development during gestation in Tibetan pigs

Objective  To investigate the alternations of the mammary gland morphology and of the marker protein expression, related hormones and signaling pathways of mammary gland development during gestation in Tibetan pigs.

Method  The pigs were slaughtered, and serum and the mammary glands of the third and fourth pairs were collected at 33, 50, 75 and 90 days of gestation. HE staining was used to observe the changes in mammary gland morphology. The ELISA kit was used to detect the serum levels of hormones related to mammary gland development such as estradiol (E2), progesterone (P) and prolactin (PRL). Western blot method was used to examine the expressions of marker proteins such as E74-like factor 5 (Elf- 5) and perilipin 2(PLIN2) in mammary gland development, and of hormone receptors such as estrogen receptor (ERα), prolactin receptor (PRLR) and progesterone receptor (PR), as well as the activations of PI3K/AKT and Jak2/STAT5 signal pathways which were related to mammary gland development.

Result  Morphologically, the mammary glands at 33 days of gestation were mainly composed of ductal structures, and a small amount of alveolar structures appeared at 50 days. At 75 days, the alveoli developed rapidly in the mammary glands. Notably, the mammary glands were mainly composed of alveolar structures at 90 days. Correspondingly, the expression levels of the marker proteins Elf-5 and PLIN2 in mammary gland development began to increase at 50 days of gestation, with high expression levels at 75 and 90 days. Meanwhile, serum levels of E2, P and PRL all increased with the progress of gestation. The contents of E2, P and PRL reached 42.82 ng/L, 36.76 and 66.53 μg/L respectively at 90 days. In addition, the expression levels of ERα and PRLR increased at 50 days and the PR expression increased at 75 days. Furthermore, the Jak2/STAT5 and PI3K/AKT signaling pathways were significantly activated at 75 and 90 days of gestation.

Conclusion  During gestation in Tibetan pigs, the mammary glands begin to develop alveolar at 50 days, enter the rapid alveolar development stage at 75 days, with higher developmental degree at 90 days. The alternations of mammary gland morphology are accompanied with the significant increase of hormones related to mammary gland development in serum and of hormone receptor expression in mammary glands, and with the activations of the PI3K/AKT and Jak2/STAT5 pathways which are closely related to mammary gland development.