Abstract
The study examined microRNA (miRNA) expression and regulatory patterns during an entire bovine lactation cycle. Total RNA from milk fat samples collected at the lactogenesis (LAC, day1 [D1] and D7), galactopoiesis (GAL, D30, D70, D130, D170 and D230) and involution (INV, D290 and when milk production dropped to 5 kg/day) stages from 9 cows was used for miRNA sequencing. A total of 475 known and 238 novel miRNAs were identified. Fifteen abundantly expressed miRNAs across lactation stages play regulatory roles in basic metabolic, cellular and immunological functions. About 344, 366 and 209 miRNAs were significantly differentially expressed (DE) between GAL and LAC, INV and GAL, and INV and LAC stages, respectively. MiR-29b/miR-363 and miR-874/miR-6254 are important mediators for transition signals from LAC to GAL and from GAL to INV, respectively. Moreover, 58 miRNAs were dynamically DE in all lactation stages and 19 miRNAs were significantly time-dependently DE throughout lactation. Relevant signalling pathways for transition between lactation stages are involved in apoptosis (PTEN and SAPK/JNK), intracellular signalling (protein kinase A, TGF-β and ERK5), cell cycle regulation (STAT3), cytokines, hormones and growth factors (prolactin, growth hormone and glucocorticoid receptor). Overall, our data suggest diverse, temporal and physiological signal-dependent regulatory and mediator functions for miRNAs during lactation.
Highlights
The study examined microRNA expression and regulatory patterns during an entire bovine lactation cycle
Milk samples were obtained from nine cows on day[1] (D1) and D7, D30, D70, D130, D170 and D230, D290 and when milk production dropped to 5 kg/day (D5kg)[20,21,22] for RNA isolation from the fat layer and deep sequencing
Our previous data showed that miRNA deep sequence data from milk fat layer was the closest representation of mammary gland tissue validating the milk fat layer as a non-invasive source of miRNA for the study of mammary gland functions[23]
Summary
The study examined microRNA (miRNA) expression and regulatory patterns during an entire bovine lactation cycle. The roles of miRNAs in dairy lactation process or mammary gland development have been investigated using different approaches such as microarray[3], RNA sequencing[4,5,6,7] and functional analyses of specific miRNAs8–14. A role for miR-103 in the control of milk fat accumulation in goat mammary gland during lactation has been demonstrated[19] These data indicate important roles of miRNAs in mammary gland development and lactation. In order to better understand the biology underlying the bovine lactation curve, this study examined dynamic miRNA expression patterns during lactation and at each transition stage of lactation to identify key regulatory miRNAs of the lactation process. A time course analysis was applied to establish whether the expression of miRNAs is time dependent
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