Characterization of long noncoding RNA in nonlactating goat mammary glands reveals their regulatory role in mammary cell involution and remodeling.

Long noncoding RNA (lncRNA) can regulate mammary gland development and lactation physiological activities. However, the molecular genetic mechanisms of lncRNA in mammary gland involution and cell remodeling remain unclear. This work analyzed the expression characteristics and molecular functions of lncRNA in goat mammary gland tissue at the late lactation (LL), dry period (DP), and late gestation (LG) stages. Sequencing results showed that 3074 lncRNAs were identified in non-lactating goat mammary gland tissue. Statistical analysis of lncRNA length characteristics and exon number found that goat lncRNAs were shorter in length, had fewer exons, and significantly lower expression levels than those of protein-coding genes. 331 differentially expressed lncRNAs were identified in the three comparison groups (LLvsDP, DPvsLG, and LLvsLG), which indicated that the lncRNAs expression at the transcriptional level were changed during mammary involution. Interestingly, lncRNAs were more actively expressed during the dry period compared to lactation, suggesting that lncRNAs in mammary glands are developmentally specific. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses revealed that lncRNAs could regulate immune function, cell proliferation, apoptosis, hormones, substance metabolism, transport, and intercellular communication in the mammary gland through various action modes. Among them, cis-acting lncRNAs enhanced the protection of mammary gland health during the dry period and late gestation. The above reflects the particular mechanisms of lncRNA to adapt to the developmental needs of mammary involution and remodeling. Furthermore, in the lncRNA-miRNA-mRNA network associated with mammary gland development, the expression of LOC102168552 was higher in late gestation than in the dry period and late lactation. Its expression was positively correlated with PRLR and negatively correlated with chi-miR-324-3p. Overexpression of LOC102168552 in goat mammary epithelial cells cultured in vitro could up-regulate PRLR to activate the prolactin signaling pathway by competitively binding to chi-miR-324-3p, promoting cell proliferation, reducing cell cycle arrest in the G1 / S phase, and inhibiting apoptosis. However, overexpression of LOC102168552 alone did not affect mammary cell growth status and the prolactin signaling pathway. This indicates that LOC102168552 must rely on chi-miR-324-3p to inhibit mammary cell apoptosis. In conclusion, the above analysis revealed that lncRNAs in goat mammary tissue are differentially expressed at different stages of involution. As expected, lncRNAs adaptively regulate various physiological activities during mammary gland involution through multiple modes of action, in preparation for a new round of lactation. These findings provide a reference and help further understand the regulatory role of lncRNAs in mammary cell involution and remodeling.