Genome wide expression analysis of circular RNAs in mammary epithelial cells of cattle revealed difference in milk synthesis

Chronic Stress Decreases Lactation Performance

The ability to provision offspring with milk is a significant adaptive feature of mammals that allows for considerable maternal regulation of offspring beyond gestation, as milk provides complete nutrition for developing neonates. For mothers, lactation is a period of marked increases in energetic and nutritive demands to support milk synthesis; because of this considerable increase in demand imposed on multiple physiological systems, lactation is particularly susceptible to the effects of chronic stress. Here, we present work that explores the impact of chronic stress during lactation on maternal lactation performance (i.e., milk quality and quantity) and the expression of key milk synthesis genes in mammary tissue using a Sprague-Dawley rat model. We induced chronic stress using a well-established, ethologically relevant novel male intruder paradigm for 10 consecutive days during the postpartum period. We hypothesized that the increased energetic burden of mounting a chronic stress response during lactation would decrease lactation performance. Specifically, we predicted that chronic exposure to this social stressor would decrease either milk quality (i.e., composition of proximate components and energy density) or quantity. We also predicted that changes in proximate composition (i.e., lipid, lactose, and protein concentrations) would be associated with changes in gene expression levels of milk synthesis genes. Our results supported our hypothesis that chronic stress impairs lactation performance. Relative to the controls, chronically stressed rats had lower milk yields. We also found that milk quality was decreased; milk from chronically stressed mothers had lower lipid concentration and lower energy density, though protein and lactose concentrations were not different between treatment groups. Although there was a change in proximate composition, chronic stress did not impact mammary gland expression of key milk synthesis genes. Together, this work demonstrates that exposure to a chronic stressor impacts lactation performance, which in turn has the potential to impact offspring development via maternal effects.

Identification and Characterization of circRNAs in Non-Lactating Dairy Goat Mammary Glands Reveal Their Regulatory Role in Mammary Cell Involution and Remodeling

This study conducted transcriptome sequencing of goat-mammary-gland tissue at the late lactation (LL), dry period (DP), and late gestation (LG) stages to reveal the expression characteristics and molecular functions of circRNAs during mammary involution. A total of 11,756 circRNAs were identified in this study, of which 2528 circRNAs were expressed in all three stages. The number of exonic circRNAs was the largest, and the least identified circRNAs were antisense circRNAs. circRNA source gene analysis found that 9282 circRNAs were derived from 3889 genes, and 127 circRNAs' source genes were unknown. Gene Ontology (GO) terms, such as histone modification, regulation of GTPase activity, and establishment or maintenance of cell polarity, were significantly enriched (FDR < 0.05), which indicates the functional diversity of circRNAs' source genes. A total of 218 differentially expressed circRNAs were identified during the non-lactation period. The number of specifically expressed circRNAs was the highest in the DP and the lowest in LL stages. These indicated temporal specificity of circRNA expression in mammary gland tissues at different developmental stages. In addition, this study also constructed circRNA-miRNA-mRNA competitive endogenous RNA (ceRNA) regulatory networks related to mammary development, immunity, substance metabolism, and apoptosis. These findings help understand the regulatory role of circRNAs in mammary cell involution and remodeling.

Genome-Wide Association Studies of Live Weight at First Breeding at Eight Months of Age and Pregnancy Status of Ewe Lambs

This study estimated genetic parameters and identified candidate genes associated with live weight, and the occurrence of pregnancy in 1327 Romney ewe lambs using genome-wide association studies. Phenotypic traits considered were the occurrence of pregnancy in ewe lambs and live weight at eight months of age. Genetic parameters were estimated, and genomic variation was assessed using 13,500 single-nucleotide polymorphic markers (SNPs). Ewe lamb live weight had medium genomic heritability and was positively genetically correlated with occurrence of pregnancy. This suggests that selection for heavier ewe lambs is possible and would likely improve the occurrence of pregnancy in ewe lambs. No SNPs were associated with the occurrence of pregnancy; however, three candidate genes were associated with ewe lamb live weight. Tenascin C (TNC), TNF superfamily member 8 (TNFSF8) and Collagen type XXVIII alpha 1 chain (COL28A1) are involved in extracellular matrix organization and regulation of cell fate in the immune system. TNC may be involved in ewe lamb growth, and therefore, could be of interest for selection of ewe lamb replacements. The association between ewe lamb live weight and TNFSF8 and COL28A1 is unclear. Further research is needed using a larger population to determine whether the genes identified can be used for genomic selection of replacement ewe lambs.

CircRNA Profiling of Skeletal Muscle in Two Pig Breeds Reveals CircIGF1R Regulates Myoblast Differentiation via miR-16

Muscle development is closely related to meat quality and production. CircRNAs, with a closed-ring structure, have been identified as a key regulator of muscle development. However, the roles and mechanisms of circRNAs in myogenesis are largely unknown. Hence, in order to unravel the functions of circRNAs in myogenesis, the present study explored circRNA profiling in skeletal muscle between Mashen and Large White pigs. The results showed that a total of 362 circRNAs, which included circIGF1R, were differentially expressed between the two pig breeds. Functional assays showed that circIGF1R promoted myoblast differentiation of porcine skeletal muscle satellite cells (SMSCs), while it had no effect on cell proliferation. In consideration of circRNA acting as a miRNA sponge, dual-luciferase reporter and RIP assays were performed and the results showed that circIGF1R could bind miR-16. Furthermore, the rescue experiments showed that circIGF1R could counteract the inhibitory effect of miR-16 on cell myoblast differentiation. Thus, circIGF1R may regulate myogenesis by acting as a miR-16 sponge. In conclusion, this study successfully screened candidate circRNAs involved in the regulation of porcine myogenesis and demonstrated that circIGF1R promotes myoblast differentiation via miR-16, which lays a theoretical foundation for understanding the role and mechanism of circRNAs in regulating porcine myoblast differentiation.

Non-coding transcriptomic profiles in the sheep mammary gland during different lactation periods

Sheep milk production is a dynamic and multifactorial trait regulated by diverse biological mechanisms. To improve the quality and production of sheep milk, it is necessary to understand the underlying non-coding transcriptomic mechanisms. In this study, ribonucleic acid-sequencing (RNA-seq) was used to profile the expression of microRNAs (miRNAs) and circular RNAs (circRNAs) in the sheep mammary gland at three key lactation time points (perinatal period, PP; early lactation, EL; and peak lactation, PL). A total of 2,369 novel circRNAs and 272 miRNAs were profiled, of which 348, 373, and 36 differentially expressed (DE) circRNAs and 30, 34, and 7 DE miRNAs were detected in the comparison of EL vs. PP, PL vs. PP, and PL vs. EL, respectively. A series of bioinformatics analyses including functional enrichment, machine learning prediction, and competing endogenous RNA (ceRNA) network analyses were conducted to identify subsets of the potential candidate miRNAs (e.g., oar_miR_148a, oar_miR_362, and oar_miR_432) and circRNAs (e.g., novel_circ_0011066, novel_circ_0010460, and novel_circ_0006589) involved in sheep mammary gland development. Taken together, this study offers a window into the dynamics of non-coding transcriptomes that occur during sheep lactation and may provide further insights into miRNA and circRNA that influence sheep mammary gland development.