In article <000401be07aa$c076d2c0$ab809bd0 at default>, browley at GALAXY.UCR.EDU
says...
>>A short while ago, someone on this list alluded to evidence that some
>dividing cells can maintain telomere length in the absence of
>telomerase or telomerase expression. I.e., there are other techniques
>a cell can use to offset telomere shortening. I'm interested in this
>work; anybody remember what the reference was?
>>Brian Rowley
Brian,
There are actually quite a few studies showing an alternative mechanisms for
maintaining telomeric length. These include transposon maintenance in
Drosophila and recombinant DNA processes in the mosquito Anopheles.
But since you specifically asked about telomeric maintenance in humans the
following studies may be of interest.
That alternative mechanisms of telomeric maintenance is required is described
in: (Hum Mol Genet 1997 Jun;6(6):921-6 "The telomere lengthening mechanism in
telomerase-negative immortal human cells does not involve the telomerase RNA
subunit.", Bryan TM, Marusic L, Bacchetti S, Namba M, Reddel RR.)
Possible alternative maintenance systems were described in: (Chromosoma 1997
Jul;106(2):63-69, "Telomere maintenance without telomerase.", Biessmann H,
Mason JM.)
More recently a negative feedback system of telomeric length maintenance was
described in: (Exp Cell Res 1998 May 1;240(2):333-9, "Dissociation of
telomere dynamics from telomerase activity in human thyroid cancer cells.",
Jones CJ, Soley A, Skinner JW, Gupta J, Haughton MF, Wyllie FS, Schlumberger
M, Bacchetti S, Wynford-Thomas D.)
A very interesting study on the effects of quiescence on telomeric shortening
and alternative telomere maintenance systems was detailed in: (Free Radic
Biol Med 1998 Apr;24(6):885-93, "Accelerated telomere shortening in
fibroblasts after extended periods of confluency.", Sitte N, Saretzki G, von
Zglinicki T.) I recommend this study to show some of the complexities
involved in telomeric maintenance.
Specific genes on chromosome 2 of Mus musculus have also been described that
determine telomeric length during development and human analogues are thought
to exist. This would help explain some of the results pointed out by these
studies.
Thomas Mahoney, Pres.
Lifeline Laboratories, Inc.
http://home.earthlink.net/~excelife/index.html
