THE PROGRESSIVE RISE IN THE EXPRESSION OF ALPHA-CRYSTALLIN-B CHAIN INHUMAN ENDOMETRIUM IS INITIATED DURING THE IMPLANTATION WINDOW - MODULATION OF GENE-EXPRESSION BY STEROID-HORMONES

Human endometrium undergoes sequential changes during the menstrual cy cle and becomes receptive to implantation during a defined period in t he secretory phase. We attempted to identify the genes expressed durin g this period by representational difference analysis (RDA), When the cDNAs of a proliferative endometrium were used as the driver and the c DNAs of a post-ovulatory day 5 endometrium were used as the tester, a number of bands were identified by RDA. RNA of the cloned RDA products revealed that the majority of the clones contained a fragment of a cD NA identical to that of a crystallin B chain. Northern blot analysis s howed that the expression of the a crystallin B chain mRNA was absent during the proliferative phase. The expression of the mRNA of a crysta llin B chain first appeared in the secretory phase, progressively incr eased during this phase and peaked in the late secretory endometria. T he pattern of expression of a crystallin B chain mRNA in the endometri um of mature cycling baboons (Papio anubis) was similar to that seen i n human endometrium. As revealed by Western blot analysis, the express ion of the a crystallin B chain protein in human endometrium followed a pattern of expression similar to its mRNA. At the cellular level, th e immunoreactive protein first appeared in the surface epithelial cell s of human endometrium within the implantation window without signific ant immunoreactivity in the underlying glandular cells. During the mid - and late secretory phases, the intensity of staining in the epitheli al cells was enhanced and an intense immunoreactivity was developed in the glandular epithelium. a crystallin B chain was virtually an epith elial product and no immunoreactivity for this protein was detectable in the stromal cells, endothelial cells or lymphoid cells. The express ion of a crystallin B chain could be regulated, by medroxy progesteron e acetate as well as by oestrogen withdrawal, in human endometrial car cinoma cells (EnCa-101), transplanted to nude mice. Based on the data presented here, the known function of a crystallin B chain and its dis tinct pattern of expression in human endometrium, we suggest that this protein is an important factor within the molecular repertoire that m akes endometrium receptive to implantation.