Expression of Telomerase Reverse Transcriptase Subunit (TERT) and Telomere Sizing in Pig Ovarian Follicles

Abstract

(DF) S U M M A R Y Telomerase is crucial for chromosome stability because it maintains telomere length. Little is known about telomerase in ovarian follicles, where an intense cell division is crucial to sustain estrous cycle and to drive oocyte development. The present research was performed to detect, by immunohistochemistry, the distribution of telomerase catalytic subunit (TERT) during folliculogenesis and to study the effect of TERT expression on telomeres. To this aim, telomere length has been measured on fluorescence in situ hybridization (FISH)-processed sections either in follicular or in germ cells. In primary and preantral follicles, TERT was observed in granulosa and in germ cells, with a typical nuclear location. During antral differentiation, only somatic cells close to the antrum (antral layer) and cumulus cells maintained TERT expression. The relative oocytes located TERT in the ooplasm independent from the process of meiotic maturation. FISH results indicate that a correlation exists between TERT expression and telomere size. In fact, progressively bigger telomeres were observed from preantral to antral follicles where longer structures were recorded in cells of the cumulus oophorus and of the antral layer than those of the basal one. Stable and elongated telomeres were detected in fully grown oocytes that lost the functional TERT distribution within the nucleus. (J Histochem Cytochem 54:443-455, 2006)

Estrogen deficiency reversibly induces telomere shortening in mouse granulosa cells and ovarian aging in vivo

“…Our recent studies showing that estrogen deficiency caused telomerase inhibition in the adrenal gland (Bayne et al, 2008) suggest that estrogen links the regulation of telomere homeostasis in steroidogenic organs in mice. The regulation of ovarian telomerase, present in a number of species including mice, rats, cows, pigs and humans (Lavranos et al, 1999;Rodgers et al, 2001;Yamagata et al, 2002;Baykal et al, 2004;Russo et al, 2006), is likely to be physiological, underlying major functions of the ovary. Our findings that estrogen increases telomere length in 3-4-week-old ArKO mice suggest that estrogen deficiencyassociated telomerase inhibition is due to the lack of estrogen stimulation of telomerase, since the inhibition is reversed by estrogen replacement therapy.…”

Modifications in chromatin morphology and organization during sheep oogenesis

“…To determine telomere size, using the fluorescence in situ hybridization (FISH) technique, the oocytes were processed within their follicle structures, according to Russo et al (2006), dehydrated through ethanol series, and then embedded in paraffin wax.…”

“…The TERT component of telomerase is the primary determinant for enzyme activity and its expression is correlated to cells with telomere elongation (Cong et al, 1999;Misiti et al, 2000;Wang et al, 2000). Recently, TERT component has been related to the process of telomere rearrangement in pig germ cells during oogenesis where the presence of the enzyme within the nucleus has been strictly correlated to progressive telomere elongation (Russo et al, 2006).…”

Telomerase in the ovary

“…Analysis (by immunohistochemistry and fluorescence in situ hybridization) of the distribution of TERT during folliculogenesis and its correlation with telomeres in porcine ovarian primary and preantral follicles showed that TERT is expressed in granulosa cells with a typical nuclear location, and that its expression correlates with the size of telomeres. Long telomeres were seen from preantral to antral follicles (Russo et al 2006). Telomerase activity was detected in two distinct populations of porcine granulosa cells: relatively undifferentiated granulosa cells isolated from small (1-2 mm) antral follicles and differentiated cells with advanced functionality obtained from large (5-7 mm) antral follicles (Tomanek et al 2008).…”