Estrogen receptor-alpha messenger RNA variants that lack exon 5 or exon 7 are coexpressed with wild-type form in human endometrium during all phases of the menstrual cycle.
OBJECTIVE
We have assessed the expression levels of messenger RNA for estrogen receptor-alpha and splice variants lacking exon 5 or exon 7 that presumably exert dominant positive (splice variants lacking exon 5) and negative (splice variants lacking exon 7) effects, respectively, on estrogen responses in the human endometrium.


METHODS
This was a prospective study that was conducted at an academic community-based hospital. The patients, aged 18 to 40 years, underwent hysterectomy for benign gynecologic causes. Eighty-one endometrial specimens (46 proliferative, 35 secretory) were analyzed with the use of reverse transcription-polymerase chain reaction assay for the messenger RNA levels of estrogen receptor-alpha, and splice variants lacking exon 5 and exon 7.


RESULTS
Wild-type estrogen receptor-alpha and splice variants splice variants lacking exon 5 and lacking exon 7 messenger RNAs were detected in all endometrial specimens throughout the menstrual cycle. In addition, a double-splice estrogen receptor-alpha messenger RNA variant (splice variants lacking exon 5 and exon 7) was detected at constant low levels of expression. Semiquantitative analysis showed higher levels of estrogen receptor-alpha messenger RNA in the early and mid proliferative endometrial phases than in late proliferative and secretory endometrium ( P <.05). The splice variant lacking exon 7 messenger RNA expression level was about 10-fold higher than the splice variant lacking exon 5 messenger RNA relative to wild-type estrogen receptor-alpha messenger RNA ( P <.001). The expression of splice variants lacking exon 5 compared with wild-type estrogen receptor-alpha messenger RNA is relatively constant throughout endometrial development. In contrast, an examination of the ratio of the levels of splice variants lacking exon 7 to wild-type estrogen receptor-alpha messenger RNA indicated a small, but significantly higher, splice variant lacking exon 7 level in the mid secretory phase (postovulatory days 5-8) than the mid proliferative and early secretory phases ( P <.05).


CONCLUSIONS
We found no evidence of differential coexpression of the positive dominant estrogen receptor variant, splice variants lacking exon 5, with wild-type estrogen receptor-alpha. We did find that the dominant negative splice variant lacking exon 7 was slightly increased relative to wild-type estrogen receptor-alpha in the postovulatory phase. Future investigation is required to suggest the biologic significance of the observed increased relative expression of the splice variants lacking exon 7 in secretory endometrium and to determine the function of splice variants lacking exon 5 and splice variants lacking exon 7.
Marshburn
Paul B
PB
Department of Obstetrics and Gynecology, Division of Reproductive Endocrinology and Infertility, Carolinas Medical Center, 1000 Blythe Boulevard, Charlotte, NC 28232, USA. paul.marshburn@carolinashealthcare.org
Zhang
Jian
J
Bahrani-Mostafavi
Zahra
Z
Mostafavi
Behrooz Z
BZ
Marroum
Marie-Claire
MC
Mougeot
Jean-Luc C
JL
Roshon
Michael J
MJ
D017398:Alternative Splicing; D015139:Blotting, Southern; D004591:Electrophoresis, Polyacrylamide Gel; D004717:Endometrium / Q000378:metabolism*; D047628:Estrogen Receptor alpha; D005091:Exons; D005260:Female; D015870:Gene Expression; D014644:Genetic Variation; D006801:Humans; D008597:Menstrual Cycle / Q000502:physiology*; D012333:RNA, Messenger / Q000378:metabolism*; D011960:Receptors, Estrogen / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017423:Sequence Analysis, RNA
D047628:Estrogen Receptor alpha; D012333:RNA, Messenger; D011960:Receptors, Estrogen