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Telomere Length in Male Germ Cells Is Inversely Correlated with Telomerase Activity¹

^a Department of Cell Biology, Georgetown University Medical Center, Washington, District of Columbia 20007

ABSTRACT

Telomeres, the noncoding sequences at the ends of chromosomes, progressively shorten with each cellular division. Spermatozoa have very long telomeres but they lack telomerase enzymatic activity that is necessary for de novo synthesis and addition of telomeres. We performed a telomere restriction fragment analysis to compare the telomere lengths in immature rat testis (containing type A spermatogonia) with adult rat testis (containing more differentiated germ cells). Mean telomere length in the immature testis was significantly shorter in comparison to adult testis, suggesting that type A spermatogonia probably have shorter telomeres than more differentiated germ cells. Then, we isolated type A spermatogonia from immature testis, and pachytene spermatocytes and round spermatids from adult testis. Pachytene spermatocytes exhibited longer telomeres compared to type A spermatogonia. Surprisingly, although statistically not significant, round spermatids showed a decrease in telomere length. Epididymal spermatozoa exhibited the longest mean telomere length. In marked contrast, telomerase activity, measured by the telomeric repeat amplification protocol was very high in type A spermatogonia, decreased in pachytene spermatocytes and round spermatids, and was totally absent in epididymal spermatozoa. In summary, these results indicate that telomere length increases during the development of male germ cells from spermatogonia to spermatozoa and is inversely correlated with the expression of telomerase activity.

FOOTNOTES

First decision: 5 January 2000.

¹ This work was supported in part by NIH grants HD 33728 (M.D.) and HD 00627 (M.V.A.).

² Correspondence: Martin Dym, Department of Cell Biology, Georgetown University Medical Center, 3900 Reservoir Road NW, Washington, DC 20007. FAX: 202 687 9864; dymm{at}gunet.georgetown.edu

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