Abstract

MicroRNAs (miRNAs) play an important role in regulating mammary gland development and lactation. We previously analyzed miRNA expression profiles in Laoshan dairy goat mammary glands at the early (20 d postpartum), peak (90 d postpartum) and late lactation (210 d postpartum) stages. To further enrich and clarify the miRNA expression profiles during the lactation physiological cycle, we sequenced miRNAs in the mammary gland tissues of Laoshan dairy goats at three newly selected stages: the late lactation (240 d postpartum), dry period (300 d postpartum) and late gestation (140 d after mating) stages. We obtained 4038 miRNAs and 385 important miRNA families, including mir-10, let-7 and mir-9. We also identified 754 differentially expressed miRNAs in the mammary gland tissue at the 3 different stages and 6 groups of miRNA clusters that had unique expression patterns. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed that GO terms such as mammary gland development (GO:0030879) and mammary gland morphogenesis (GO:0060443) and important signaling pathways, including the insulin signaling pathway (chx04910), hippo signaling pathway (chx04390) and estrogen signaling pathway (chx04915), were enriched. We screened miRNAs and potential target genes that may be involved in the regulation of lactation, mammary gland growth and differentiation, cell apoptosis, and substance transport and synthesis and detected the expression patterns of important genes at the three stages. These miRNAs and critical target genes may be important factors for mammary gland development and lactation regulation and potentially valuable molecular markers, which may provide a theoretical reference for further investigation of mammary gland physiology.

Highlights

  • The mammary gland of dairy goats is an economically important organ because of its milk production, and lactation performance is closely related to the stage and status of the mammary gland [1]

  • The identification, expression pattern analysis and functional analysis of miRNAs in the mammary glands of dairy goats could provide a deeper understanding of the posttranscriptional mechanisms of mammary gland development and lactation regulation, which would lay a theoretical foundation for revealing the mechanism by which miRNAs participate in mammary gland development and lactation regulation

  • We found that the expression levels of miR-148a-3p and miR-30d at the dry period (DP) stage were significantly lower than those at the late lactation (LL) and late gestation (LG) stages and the expression levels at the LL stage were the highest. miR-148a-3p overexpression can induce apoptosis of epithelial cells [46] and regulates cell proliferation, differentiation, and epithelial-mesenchymal transitions [47]. miR-30d can inhibit the proliferation of colon cancer cells and promote their apoptosis [48]

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Summary

Introduction

The mammary gland of dairy goats is an economically important organ because of its milk production, and lactation performance is closely related to the stage and status of the mammary gland [1]. During the reproductive cycle of dairy goats, the mammary gland undergoes repetitive processes, including repeated growth, as well as functional differentiation and degeneration, with each dynamic process accompanied by the proliferation and apoptosis of mammary epithelial cells [2]. The developmental characteristics at different physiological stages of the mammary gland make it an ideal model with which to study the regulation of lactation and signal transduction pathways related to cell proliferation, differentiation and apoptosis [4]. Changes in the physiological and structural functions of the mammary gland at different developmental stages are usually closely related to various hormones, such as growth hormone, estrogen, prolactin, and progesterone; various growth factors, such as epidermal growth factor, transforming growth factor, and amphiregulin; and microRNAs (miRNAs) that regulate gene expression [5,6,7,8]. The identification, expression pattern analysis and functional analysis of miRNAs in the mammary glands of dairy goats could provide a deeper understanding of the posttranscriptional mechanisms of mammary gland development and lactation regulation, which would lay a theoretical foundation for revealing the mechanism by which miRNAs participate in mammary gland development and lactation regulation

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