GENOMIC IMPRINTING AND THE ENDOMETRIAL CYCLE - THE EXPRESSION OF THE IMPRINTED GENE H19 IN THE HUMAN FEMALE REPRODUCTIVE-ORGANS

H19 is an imprinted maternally expressed gene, which is not translated to protein and functions as an RNA molecule. It is closely related to the oppositely imprinted paternally expressed insulin-like growth fac tor 2 (IGF-2). While the biological function of H19 is not understood, IGF-2 is a growth factor that plays a role in human follicular and en dometrial differentiation. We examined the expression of H19 in the en dometrium and ovary during the menstrual cycle by in situ hybridizatio n applied to paraffin sections of human endometrium and ovaries at dif ferent stages of differentiation. In the endometrium, H19 expression w as confined to the stroma and fluctuated with endometrial dating to re ach its peak in the late secretory stage. IGF-2 was also prominently e xpressed in late secretory endometrium, but its expression was evident both in the stroma and glandular epithelium. Expression of H19 was no t found in primordial, primary, and preantral follicles of the ovary, but prominent expression was evident in the theca of antral and cystic atretic follicles, and focal expression was noted in the granulosa of corpora lutea. An association between H19 expression during the menst rual cycle and the differentiation state of the human female reproduct ive tract, which is under hormonal control, is suggested.