Path: utzoo!attcan!uunet!lll-winken!lll-lcc!ames!ncar!boulder!sunybcs!rutgers!iuvax!silver!chiaravi
From: chiaravi@silver.bacs.indiana.edu (Lucius Chiaraviglio)
Newsgroups: sci.bio,sci.med
Subject: Re: Mortality
Summary: correction of typo in previous message; DNA methylation and aging
Keywords: necrology?
Message-ID: <1895@silver.bacs.indiana.edu>
Date: 12 Jun 88 00:20:45 GMT
References: <36@feedme.UUCP> <1894@silver.bacs.indiana.edu>
Reply-To: chiaravi@silver.UUCP (Lucius Chiaraviglio)
Organization: Department of Molecular, Cellular, and Developmental Biology at Indiana University, Bloomington
Lines: 32
Xref: utzoo sci.bio:1232 sci.med:5730

In article <1894@silver.bacs.indiana.edu> I wrote:
>	No, these mechanisms have not been determined, although it is definite
>that aging occurs at the cellular level.

	That should read as ". . .it is definite that some aspects of aging
occur at the cellular level."  That refers to the fact that mammalian cells
can only divide for a limited number of times before senescing, and then die.
I don't know if these experiments have been done for other vertebrates, but I
would presume that the results would be similar.  Note that mammalian cells
can become immortalized by mutation; this is a necessary step for the
attainment of a cancerous state but does not itself constitute a cancerous
state.

	Incidentally, this is a good place to point out that treatments which
reduce the level of methylation of DNA in mammalian cells, such as exposure to
5-aza-cytidine or 5-aza-deoxycytidine, reduce the lifespan (measured in terms
of number of divisions) of mammalian cells in tissue culture; even without
such treatment, loss of methylation correlates with aging, and occurs more
rapidly in cells of short-lived species, but not at all in immortalized cells.
Interestingly, an animal which has no methylation of its DNA in the first
place, Drosophila melanogaster, does age; however, imaginal disks (precursors
of the adult body which are stowed inside the larval body) can be serially
transferred from one larva to another indefinitely, and never quit growing as
long as this type of maintainance is kept up.

	-- Lucius Chiaraviglio
	   chiaravi@silver.bacs.indiana.edu
	   lucius@tardis.harvard.edu	(in case the first one doesn't work)
	"NO DYING ALLOWED." -- The Maytag coin-operated washing machine
		instruction poster.
	"This would be nice!" -- graffitti seen on the Maytag coin-operated
		washing machine instruction poster in the Daniels laundry
		room in Currier House at Harvard University.