Distinct dosage requirements for the maintenance of long and short telomeres in mTert heterozygous mice

Abstract

Telomerase is a ribonucleoprotein containing an essential telomerase RNA template and telomerase reverse transcriptase (TERT) that maintains telomeres. The dosage requirements for mammalian TERT in telomere length homeostasis are not known, but are of importance in cellular senescence, stem cell renewal, and cancer. Here, we characterize telomere maintenance and function upon successive breeding of mice deficient in mTert. These studies reveal a unique dosage requirement for telomere length maintenance by TERT; despite haploinsufficiency for the maintenance of long telomeres, mTert؉͞؊ mice retain minimal telomere DNA at all chromosome ends and do not exhibit the infertility typical of telomerase-deficient strains. Unlike the long (>50 kbp) average telomere lengths of wild-type laboratory mice, mTert؉͞؊ animals mice possess short telomere lengths similar to humans and wildderived mice. Unexpectedly, mTert؉͞؊ mice are ersatz carriers for genetic instability, because their mating led to accelerated genetic instability and infertility in null progeny. Thus, limiting TERT levels play a key role in the maintenance of genome integrity, with important ramifications for the maintenance of short telomeres in human cancer and aging.telomerase reverse transcriptase ͉ haploinsufficiency ͉ genetic instability ͉ telomere signal-free end T elomerase contains two essential components: the telomerase reverse transcriptase (TERT), and the telomerase RNA, which provides the template for the reverse transcription of new telomere DNA by TERT (reviewed in ref.

Murine Pif1 Interacts with Telomerase and Is Dispensable for Telomere Function In Vivo

“…In mPif1-deficient mice that already possess long telomeres, it is possible that further telomere lengthening could be offset by the intrastrand excision of telomeric DNA-a phenomenon observed in S. cerevisiae strains with very long telomeres (12,40) and in human cells deficient in telomere capping (73). It will be interesting to determine whether telomere lengthening in the absence of mPif1 occurs in other genetic backgrounds, particularly in mTert heterozygous animals or outbred murine strains, which possess a shorter average telomere length but retain telomerase activity (22,38).…”

“…Chimeric mice were produced by microinjection of independent mPif1 ϩ/Ϫ ES cell clones into E3.5 C57BL/6J blastocysts and transferred to ICR pseudopregnant foster mothers. The generation of founder mPif1 Ϫ/Ϫ lines and breeding of homozygous-null animals were performed as previously described for mTert Ϫ/Ϫ animals (22,38). The initial background is a mixture of 129J and C57BL/6J; therefore, to obtain mPif1 Ϫ/Ϫ in a homogeneous background, the mixed-genetic-background mPif1 ϩ/Ϫ mice were bred for eight generations to C57BL/6 mice and then mated together to generate mPif1 Ϫ/Ϫ mice (termed G 1 , C57BL/6).…”

Dyskerin Is a Component of the Arabidopsis Telomerase RNP Required for Telomere Maintenance

“…Essential components of the telomerase RNP are limiting in mammals and yeast. In both terc ϩ/Ϫ (TR) and tert ϩ/Ϫ embryonic stem mouse cells, telomere maintenance is compromised (10,17,27). Indeed, haploinsufficiency of hTR is directly linked to autosomal dominant DC, and the reduced hTR levels along with shorter telomeres in these patients result in disease anticipation (46).…”

Does the reservoir for self-renewal stem from the ends?

“…To illustrate just one example, two wild-type copies of mTert are sufficient to maintain long average telomere lengths, whereas mice heterozygous for mTert appear competent only for the maintenance of a minimal amount of telomeric DNA at each chromosome end (Liu et al, 2002). Mice that possess only one functional allele of mTert thus possess similar 'average' telomere lengths to mice that lack mTert altogether, and yet the former do not suffer from the same telomere instability and infertility as mTert null animals (Erdmann et al, 2004). Without measuring the telomeric DNA signal at each chromosome end, it may have been incorrectly inferred that telomere status in Hypothetical scenario for the potential for telomerase inhibition to force a cancerous stem cell into senescence/apoptosis (top) or for enforced telomerase expression to restore replicative capacity to an arrested cell (bottom).…”

“…While not immediately detrimental, deletion of either the telomerase RNA or TERT in mice leads to a loss of telomerase activity and progressive telomere shortening in all tissues (Blasco et al, 1997;Yuan et al, 1999;Liu et al, 2000;Erdmann et al, 2004). Eventually, detectable telomere DNA is lost from chromosome ends, leading to myriad consequences including genetic instability, infertility and increased apoptosis in germ cells, immune deficits due to reduced proliferation of activated T and B cells, premature loss of hair, and decreased wound healing (Hackett and Greider, 2002;Erdmann et al, 2004). In some murine genetic backgrounds, loss of telomere function predisposes to certain types of age-associated malignancies, while in other genetic contexts, short telomeres hinder tumor incidence and progression (Hackett and Greider, 2002).…”