Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.PCS 1/10/84; site mtgzz.UUCP
Path: utzoo!watmath!clyde!cbosgd!ihnp4!mhuxn!mhuxr!mhuxt!houxm!mtuxo!mtgzz!jak
From: jak@mtgzz.UUCP (j.a.kushner)
Newsgroups: net.bio
Subject: Re: Protein synthesis in red blood cells
Message-ID: <1414@mtgzz.UUCP>
Date: Thu, 14-Nov-85 14:01:42 EST
Article-I.D.: mtgzz.1414
Posted: Thu Nov 14 14:01:42 1985
Date-Received: Sat, 16-Nov-85 01:00:33 EST
References: <371@bcsaic.UUCP>
Organization: AT&T Information Systems Labs, Middletown NJ
Lines: 38

>From Scientific American article "RNA" Oct. 1985, pg. 70:
>> ...in human beings only red blood cells make hemoglobin...
>My question is, how do they do this?  I seem to remember that rbc's are
>anucleate, at least in the form that they float around in the blood
>stream.
>Any answers?

The pronormoblast is the first of the adult erythrocyte's precursors after
differentiation from the stem cell.  This is a large blast cell in the bone
marrow with a large percentage of the cell taken up by the nucleus, and some
small amount of blue-staining cytoplasm filling in the rest (this indicates
the presence of RNA).
With time, the cytoplasm develops a more pinkish appearance from the synthesis
of hemoglobin.  Also, the nucleus continues to show a more dense chromatin
pattern, until it is extruded from the rbc.  Now the mature adult erythrocyte
is ready to leave the marrow and circulate as a 'bag of hemoglobin'
transferring O2 and CO2 between the lungs and the tissues, and also acting to
buffer the blood.

>I also seem to recall that the lifetime of an rbc is quite short, as
>compared with that of other cells in the body.  Is this related with
>their being anucleate?

Partially, in that without the nucleus, there can be no further protein
synthesis.  Not only is hemoglobin production shut-off, but other vital
enzymes can no longer be synthesized.  Among the enzymes necessary for
maintaining rbc integrity are those that prevent oxidation.  Oxidation
of membrane sulfhydrils leads to rigid membranes which burst upon squeezing
through the micro-circulation, as is found in the liver and spleen.  Also,
oxidation of the hemoglobin leads to the formation of red cell inclusions
(Heinz bodies, as I recall).  These abnormalities are pitted out of the
circulating cells by RE (Reticulo-Endothelial) cells, primarily in the 
spleen.  In so doing, the lifespan of the rbc is decreased, if not ended
at that time.

Hope this helps,
Jeff Kushner
{...!ihnp4}!mtgzz!jak