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Title: Comparisons of mRNA expression for aromatase, FSH receptor, and IGF-I in the granulosa of small ovarian follicles between cattle selected and unselected for twin ovulations

Author
item Echternkamp, Sherrill
item Cushman, Robert - Bob
item SPICER, LEON - OKLA ST UNIV STILLWATER

Submitted to: Biology of Reproduction Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 2/20/2008
Publication Date: 9/1/2008
Citation: Echternkamp, S., Cushman, R., Spicer, L. 2008. Comparisons of mRNA expression for aromatase, FSH receptor, and IGF-I in the granulosa of small ovarian follicles between cattle selected and unselected for twin ovulations [abstract]. Biology of Reproduction. Special Issue:81 (Abstract #123).

Interpretive Summary:

Technical Abstract: Long-term selection of cattle for the production of twin ovulations and births has enhanced the development of preantral and antral ovarian follicles and increased the frequency of twin or triplet ovulations to greater than 60%. However, these differences have not been linked to differences in FSH secretion between the two cattle populations. The objective of this study was to compare the abundance of mRNA expression for aromatase, FSH receptor, and IGF-I in small (<5 mm) antral follicles from Twinner (n = 15) and non-Twinner (n = 15) cattle. Ovaries were collected from cyclic (d 5 or 6) cows at slaughter, and pieces of cortical tissue were fixed in 4% formaldehyde, dehydrated in ethanol and then xylene, and embedded in paraffin. Expression of mRNA was evaluated by in situ hybridization using 35S-UTP-labelled antisense and sense probes published for aromatase, FSH receptor, and IGF-I. Slides were exposed to Kodak NTB-2 emulsion for 4 wk. Aromatase and FSH receptor mRNA were localized within the granulosa cell layer. IGF-I mRNA was primarily localized within the granulosa layer and tended to be greater in cumulus cells than in other granulosa cells; presence of IGF-I mRNA in the theca layers was more variable among follicles and less intense than in granulosa cells. Silver grain density was quantified in four areas within the intact granulosa of each antral follicle (2 to 7 follicles/cow) using the Bioquant Nova Prime image analysis system. Antisense minus sense density measurements were averaged for the four replicates/follicle and the specific expression data were analyzed for a genetic line effect using SAS Proc Mixed for repeated measurements. Abundance of mRNA for aromatase (17.54 ± 1.63 vs. 7.77 ± 1.41% specific grains; P < 0.01) and for FSH receptor (11.34 ± 1.28 vs. 7.48 ± 1.08% specific grains; P < 0.05) was greater in the granulosa of small follicles from Twinner than non-Twinner cows, respectively, whereas IGF-I mRNA expression in the granulosa did not differ between cattle populations (14.61 ± 2.82 vs. 13.69 ± 2.34% specific grains). The expression of mRNA for FSH receptor and IGF-I was correlated positively (r = 0.28; P = 0.02). Evaluated small antral follicles from Twinner cows tended to be smaller in diameter than those from non-Twinner cows (1.9 ± 0.1 vs. 2.3 ± 0.1 mm; P = 0.08), but means for the thickness of the granulosa layer did not differ between the two genetic groups (76.8 ± 19. 2 vs. 75.0 ± 16.0 microns, respectively). The increased abundance of aromatase and FSH receptor mRNA in small antral follicles from ovaries of Twinner cows implicate genetic differences in the differentiation of small antral follicles to FSH responsiveness between cattle selected and unselected for twin ovulations.