Rating of putative housekeeping genes for quantitative gene expression analysis in cyclic and early pregnant equine endometrium

The aim was an evaluation of a set of housekeeping genes (HKGs) to be used in the normalization of gene expression in the equine endometrium. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), hypoxanthine ribosyl transferase 1 (HPRT1), ubiquitin B (UBB), tubulin alpha 1 (TUBA1), ribosomal protein L32 (RPL32), beta-2-microglobulin (B2M), 18S rRNA (18S), and 28S rRNA (28S) HKGs were evaluated using real-time PCR and were compared in different physiological stages of the endometrium. Endometrial biopsies were obtained from mares on day of ovulation (d0, n = 4), at late diestrus (LD, n = 4), after luteolyis (AL, n = 4) of the cycle and on days 14 (P14; n = 3), 18 (P18, n = 3) and 22 (P22; n = 3) of pregnancy. A model based on REML with support of descriptive statistics was proposed in accordance with experimental design and was further confirmed with principal component analysis (PCA). Results were compared with widely used software including geNorm, BestKeeper, and NormFinder. Results indicated that GAPDH was the most stable HKG and RPL32 was ranked as the second best. 18S and 28S were found to be the least stable. The proposed model, PCA, geNorm, and BestKeeper were in agreement in detecting the most stable and the least stable HKGs in the equine endometrium during the estrous cycle and early pregnancy.