Abstract: Abstract： Objective To screen and identify the key miRNAs during mammary gland development and milk secretion of rats. Methods Gene U6 was taken as interior label gene by real time-PCR to compare the differences of expression levels of miR-142-3p and miR-145-3p in the mammary gland, liver, heart, spleen, lung, kidney, ovary and uterus after 21 postpartum. Moreover, the expressions of miR-142-3p and miR-145-3p in different stages (1, 7 and 21 d) of lactation were summarized. Results There was significant difference in miR-142-3p in lactation 21 d between different tissues. The expression of miR- 142-3p was significantly higher in mammary gland than that in heart, spleen, lung, kidney, ovary and uterus tissues, which was second only to the expression in liver (P < 0.05). The expression of miR-145-3p was significantly higher in mammary gland than that in liver, spleen and kidney. There was no significant difference in the expression of miR-145-3p between heart, lung, ovary and uterus (P > 0.05). Furthermore, the relative expression level of miR-142-3p was continuing downward continued to decline in breast at different stages of lactation, while the relative expression level of miR-145-3p was up-regulated after down- regulating. Conclusion miR-142-3p and miR-145-3p are differentially expressed in different tissues and physiological periods in rats. In addition, miR-142-3p can regulate the growth of mammary gland and the formation of lactation by targeting prolactin receptor (Prlr), miR-145-3p may have the same function with miR-145 and miR-145-5p.

Key words: mammary glands, animal, microRNAs, liver, heart, spleen, lung, kidney, ovary, uterus, rats, Sprague-Daw? ley, miR-142-3p, miR-145-3p, real time-PCR