Dynamic transcriptome profiling of bovine endometrium during the oestrous cycle

Fertility problems are the main reason for slaughter of
high-performance milk cows, because prolonged calving intervals
result in financial losses for the farmer and retard genetic
progress. Genetic improvement of fertility would be of great
benefit, but functional traits for effective selection are missing.
Recent advances in functional genomics tools like DNA microarrays
could be the key to identify gene expression patterns in the
endometrium that correlate with maternal fertility. Therefore, a
bovine oviduct and endometrium cDNA array was established that
contains a set of 1,440 cDNA clones and long oligonucleotides
representing 950 different genes. The major part of these genes
results from a series of differential gene expression studies in
endometrium (different stages of the oestrous cycle, day 18 and day
15 pregnant vs. nonpregnant) and oviduct epithelial cells
(different stages of the oestrous cycle). Using this custom-made
cDNA array the response of the endometrium was studied to the
changing hormonal environment during the bovine oestrous cycle.
Endometrium samples were recovered from Simmental heifers
slaughtered on day 0 (oestrus), 3.5 (metoestrus), 12 (dioestrus)
and 18. The latter group was divided into animals with high (late
dioestrus) and low progesterone levels (preoestrus). Statistical
analysis with the Significance Analysis of Microarrays (SAM) method
revealed 269 genes exhibiting significant changes in their
transcript levels during the oestrous cycle in distinct temporal
patterns. Two major types of expression profiles were observed,
which showed the highest mRNA levels during the oestrus phase or
the highest levels during the luteal phase, respectively. A minor
group of genes exhibited the highest mRNA levels on day 3.5. Gene
ontology (GO) analyses revealed GO categories related to
extracellular matrix remodelling, transport, and cell growth and
morphogenesis enriched at oestrus, whereas immune response and
particular metabolic pathways were overrepresented at dioestrus.
Generation of gene interaction networks uncovered genes possibly
involved in biological processes important for establishment of
early pregnancy, such as endometrial remodelling (e.g. collagen
genes, MMP2, TIMP1), regulation of angiogenesis (e.g. ANGPTL2,
TEK), regulation of invasive growth (e.g. PCSK5, tight junction
proteins, ITGB4), cell adhesion (e.g. MUC16, LGALS3BP) and embryo
feeding (e.g. SLC1A1, ENPP1). Localisation of mRNA expression in
the endometrium was analysed for CLDN4, CLDN10, TJP1, PCSK5,
MAGED1, and LGALS1. Future application of the BOE array, based on
the knowledge from the cycle study, could be the use in systematic
studies of interactions between the metabolic status and
functionality of the endometrium to identify genes that could be
used for differential diagnosis of fertility problems.