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Effects of nutrient restriction and dietary selenium on expression of gap junctional protein connexin (CX) 43 in fetal ovaries obtained from sheep in late pregnancy; implications for developmental programming.

The fetal ovaries represent a type of tissue which grows rapidly. This process must be tightly regulated and requires cellular interactions which may be mediated through contact-independent and contact-dependent gap junctional communication. Gap junctions are composed of connexin proteins that form intercellular channels allowing for direct communication among cells, and are involved in growth control. During folliculogenesis in the fetus, primordial follicles develop to primary follicles, then secondary, and antral follicles. Maternal diet can affect fetal growth and organ function. Selenium (Se) is a mineral that has diverse biological functions. Selenium affects cellular proliferation in selected organs. We hypothesized that maternal diet will affect expression of Cx43 in fetal ovaries. Therefore, the aim of this study was to determine if maternal consumption of differing levels of energy and Se in diet impacts expression of Cx43 protein in fetal ovaries.

Sheep (n=26) were fed a maintenance (M; 2.12 Mcal/kg) or an energy restricted (R; 60% of maintenance) diet with high (H) Se (81.5 [micro]g/kg body weight) or adequate (A) Se (7.4 [micro]g/kg body weight) concentration from 21 days before breeding to day 135 of pregnancy. On day 135 of pregnancy fetal ovaries were collected and fixed. Ovaries (n=5-7/nutrition treatment) were sectioned and then immunostained for the presence of Cx43. To determine the Cx43 expression (percentage of positive staining out of the total follicle or tissue area), digital images of the tissues containing primary (total 33; 6-11/treatment), secondary (total 118; 19-36/treatment) and antral (total 153; 14-67/treatment) follicles were taken and analyzed using a computerized image analysis program. For primary and secondary follicles, Cx43 expression was determined in the granulosa layer; but for antral follicles, granulosa and thecal layers were analyzed separately.

Cx43 protein was expressed in fetal ovaries and was localized to primordial follicles, the granulosa layer of primary, secondary, and antral follicles, to theca layer of antral follicles, and an area between the ooeyte and granulosa layer. Cx43 expression was greater (P<0.001) in granulosa cells of antral follicles than in primary or secondary follicles (1.5 [+ or -] 0.1 vs. 0.5 [+ or -] 0.1 and 0.6 [+ or -] 0.05%). Cx43 expression was greater (P<0.001) in granulosa than theca cells of antral follicles (1.5 [+ or -] 0.1 vs. 0.6 [+ or -] 0.1%). For primary and secondary follicles, maternal diet did not affect Cx43 expression. For granulosa and theca cells of antral follicles, Cx43 expression was greater (P<0.01) in ewes fed M diet with HSe than any other treatment groups.

These results demonstrate that 1) expression of Cx43 increases with follicular development from primordial to antral stage; 2) expression of Cx43 in granulosa layer is greater than in theca layer which is likely due to the avascular nature of the granulosa layer, and 3) both level of energy and Se in maternal diet affect Cx43 expression in antral follicles. These results emphasize the importance of maternal diet in fetal growth and development.

Supported by USDA-NRICGP grants 2005-35206-15281, P20 RR016741 from the INBRE program of the National Center for Research Resources, and ND Hatch Project NDO1712.
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Author:Soni, Dheeraj; Billings, Samantha; Vonnahme, Kimberly A.; Bilski, Jerzy; Caton, Joel S.; Redmer, Dal
Publication:Proceedings of the North Dakota Academy of Science
Article Type:Report
Geographic Code:1USA
Date:Apr 1, 2009
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