Role of miRNAs in mammary gland development and lactation

Role of miRNAs in mammary gland development and lactation

 

Palaniappan Ramanathan

University of Colorado Denver

 

Executive Summary:

1. Specific Objective: To produce a functional annotation of
miRNAs active during bovine lactation by analyzing currently
available data from different species.

(i)
Recently published mouse miRNA expression data during mammary gland
development (Avril-Sassen et al., 2009) was obtained from NCBI Gene
Expression Omnibus (GSE15055) and the mean expression of the seven
major clusters (100 miRNAs) differentially expressed (DE) during
virgin (V), pregnancy (P), lactation (L) and involution (I) was
reported relative to their expression in virgin day 12 mammary glands
(Supplementary File 1 – Sheet 1) and the differentially
expressed miRNA during Lactation Day 5 (fold change > 1.5) are
reported (Supplementary File 1 – Sheet 2).

(ii)
Similarly the gene expression data (GSE15054) from the same study
(Avril-Sassen et al., 2009) was analyzed and the mean expression was
reported relative to virgin day 12 (Supplementary file 2 – Sheet 1) and the differentially expressed (DE) genes during Lactation
Day 5 (fold change > 2) are reported (Supplementary file 2 – Sheet 2). Predicted miRNA targets for the differentially
expressed miRNAs in L5 were obtained from miRbase.
Predicted targets of both L5 down-regulated and up-regulated miRNAs
were then correlated with the DE genes from Lactation day 5 to
identify overlaps (Supplementary File 3 – Sheet 1 & 2).
Negatively correlated target genes are highlighted in red as that’s
the predominant mode of miRNA regulation.

(iii)
According to the latest miRBase Release 15 there are about 675 bovine
miRNAs including most of the 59 distinct miRNAs identified from
cattle mammary gland (32 miRNAs) and adipose tissues by RNA cloning
(Gu et al., 2007). Some of these 32 miRNAs expressed in the bovine
mammary gland are located in Quantitative trait loci (QTL) regions
associated with milk (milk yield, protein yield, protein percent, fat
yield, fat percent) as well as mastitis traits (SCS) (Table S5 from Ogorevc et al 2009) (Ogorevc et al., 2009). This Table also
includes some predicted putative target sites within candidate genes
for lactation. Most of these 32 miRNAs, except three miRNAs –
bta-mir-29a, bta-mir-191, bta-mir-374 were differentially expressed
in the mouse mammary gland and their expression is listed in
Supplementary File 4.

(iv)
The differentially expressed miRNAs in mouse mammary gland were
compared to a oligonucleotide array experiment (180 miRNAs) performed
in a mouse mammary epithelial cell line HC11 which can differentiate
and secrete milk proteins upon stimulation with lactogenic hormones –
Dexamethasone, Insulin and Prolactin (DIP) (Tanaka et al., 2009).
There was a significant overlap of miRNAs differentially expressed in
HC11 cells – DIP (-) vs DIP (+) with those DE in the mouse (33%)
and the overlaps are shown in Supplementary file 5 (Sheet 1 & 3).

(v)
Finally the differentially expressed miRNAs which showed negative
correlation with lactation candidate genes (milk proteins and lipid
synthesis genes) are listed in Supplementary File 6.

2.
Significance to Field:
Functional annotation of microRNAs which
have been termed as regulators of the regulators will be valuable for
the dairy industry as it provides an additional level of
understanding of the gene expression regulatory networks in the
mammary gland during lactation.

References

Avril-Sassen, S., L.D. Goldstein, J. Stingl, C. Blenkiron, J. Le
Quesne, I. Spiteri, K. Karagavriilidou, C.J. Watson, S. Tavare, E.A.
Miska, and C. Caldas. 2009. Characterisation of microRNA expression
in post-natal mouse mammary gland development. BMC Genomics.
10:548.

Gu, Z., S. Eleswarapu, and H. Jiang. 2007. Identification and
characterization of microRNAs from the bovine adipose tissue and
mammary gland. FEBS Lett. 581:981-8.

Ogorevc, J., T. Kunej, A. Razpet, and P. Dovc. 2009. Database of
cattle candidate genes and genetic markers for milk production and
mastitis. Anim Genet. 8:8.

Tanaka, T., S. Haneda, K. Imakawa, S. Sakai, and K. Nagaoka. 2009. A
microRNA, miR-101a, controls mammary gland development by regulating
cyclooxygenase-2 expression. Differentiation. 77:181-7.