Kisspeptins are the peptide products of KISS1 gene, which operate via the G - protein-coupled receptor GPR54. These peptides have emerged as essential upstream regulators of neurons secreting gonadotropin-releasing hormone (GnRH), the major hypothalamic node for the stimulatory control of the hypothalamic–pituitary– gonadal (HPG) axis. The present study detected the polymorphisms of caprine KISS1 gene in three goat breeds and investigated the associations between these genetic markers and litter size.

MicroRNAs (miRNAs) have a great influence on various physiological functions. A lot of high-throughput sequencing (HTS) research on miRNAs has been executed in the caprine mammary gland at different lactation periods (common milk lactation and dry period), but little is known about differentially expressed miRNAs in the caprine mammary gland of colostrum and peak lactation periods. This study identified 131 differentially expressed miRNAs (P < 0.05 and log2 colostrum normalized expression (NE)/peak lactation NE > 1 or log2 colostrum NE/peak lactation NE < −1), including 57 known miRNAs and 74 potential novel miRNAs in the colostrum and peak lactation libraries. In addition, compared with differentially expressed miRNAs in the peak lactation period, 45 miRNAs in the colostrum lactation period were remarkably upregulated, whereas 86 miRNAs were markedly downregulated (P < 0.05 and log2 colostrum NE/peak lactation NE > 1 or log2 colostrum NE/peak lactation NE < −1). The expressions of 10 randomly selected miRNAs was analyzed through stem-loop real-time quantitative PCR (RT-qPCR). Their expression patterns were the same with Solexa sequencing results. Pathway analysis suggested that oestrogen, endocrine, adipocytokine, oxytocin and MAPK signalling pathways act on the development of mammary gland and milk secretion importantly. In addition, the miRNA-target-network showed that the bta-miR-574 could influence the development of mammary gland and lactation by leptin receptor (LEPR), which was in the adipocytokine signalling pathway. Chr5_3880_mature regulated mammary gland development and lactation through Serine/threonine-protein phosphatase (PPP1CA), which was in the oxytocin signalling pathway. Our finding suggested that the profiles of miRNAs were related to the physiological functions of mammary gland in the colostrum and peak lactation periods. The biological features of these miRNAs may help to clarify the molecular mechanisms of lactation and the development of caprine mammary gland.

Incremental proofs demonstrate that miRNAs, the essential regulators of gene expression, are implicated in various biological procedures, including mammary development and milk synthesis. Here, the role of miR‐574‐5p in milk synthesis, apoptosis, and proliferation of goat mammary epithelial cells (GMECs) are explored without precedent, and the molecular mechanisms for the impacts are elucidated. Small RNA libraries were constructed using GMECs transfected with miR‐574‐5p mimics and negative control followed by sequencing via Solexa technology. Overall, 332 genes were distinguishingly expressed entre two libraries, with 74 genes upregulated and 258 genes downregulated. This approach revealed mitogen‐activated protein kinase kinase kinase 9 (MAP3K9), an upstream activator of MAPK signaling, as a differentially expressed unigene. miR‐574‐5p targeted seed sequences of the MAP3K9 3′‐untranslated region and suppressed its messenger RNA (mRNA) and protein levels, correspondingly. GMECs with miR‐574‐5p overexpression and MAP3K9 inhibition showed increased cell apoptosis and decreased cell proliferation resulting from sustained suppression of MAPK pathways, while MAP3K9 elevation manifested the opposite results. miR‐574‐5p repressed the phosphorylation of members of protein kinase B (AKT)–mammalian target of rapamycin pathway via downregulating MAP3K9 and AKT3, resulting in reducing the secretion of β‐casein and triglycerides in GMECs. Finally, according to the constructed circular RNA (circRNA) libraries and bioinformatics prediction approach, we selected circ‐016910 and found it acted as a sponge for miR‐574‐5p and blocked its relevant behaviors to undertake biological effects in GMECs. The circRNA–miRNA–mRNA network facilitates further probes on the function of miR‐574‐5p in mammary development and milk synthesis.

Microplastics (MPs), as an emerging environmental pollutant, pose a grave threat to food safety and public health. However, studies on MP toxicity to organs other than the intestine remain limited, especially its link to the intestinal microbiota. To address this gap, we evaluated the potential toxicity of polystyrene (PS)-MPs to the gut and mammary glands during lactation exposure in mice. PS-MPs (~1 μm) can disrupt the intestinal barrier and cause colonic inflammation and gut microbiota dysbiosis. Moreover, they can accumulate in mammary tissue and cause inflammatory damage. Transcriptome data suggested that PS-MPs cause maternal mammary lipid metabolism disorders and ferroptosis. Fecal microbial transplant (FMT) was then performed, and it reproduced the observed leakage of the blood-milk barrier and inflammation of the mammary gland. This study demonstrated that MPs induced gut and mammary inflammation and exacerbated inflammatory damage through the gut-mammary axis. In addition, MPs caused mammary lipid disorders and ferroptosis. The findings confirmed that PS-MPs may be transported to mammalian organs other than the intestine (e.g., mammary gland) and revealed the critical role of the intestinal microbiota. These findings will provide guidance for further studies on the potential foodborne risks of MPs.