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Structure and expression of mammalian metallothioneins


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Holloway, AF 1996 , 'Structure and expression of mammalian metallothioneins', PhD thesis, University of Tasmania.

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Metallothioneins (MTs) are metal binding proteins which have been implicated
in a variety of physiological roles, including heavy metal detoxification, metal
homeostasis and free radical scavenging. In both the human and the sheep there are
multiple MT isoforms which may provide functional diversity. In both species
differential regulation and expression patterns of MT isoforms have been reported.
The work presented here investigates the expression and gene structure of MTs in
these two mammalian species; firstly investigating MT in the developing sheep brain,
and secondly studying a novel human MT isogene, MTIL. The underlying theme is to
correlate the structure and expression profiles of specific MT isoforms with their
proposed physiological functions.
Since the discovery of a novel MT in humans, MT-III, which is brain specific,
much interest has centred on the expression and role of all MTs in the brain. In this
thesis, the sheep was used as a model system in which to study the neural expression
of MT at the RNA and protein level. MT-I and -II expression was found to be
correlated with the development of glial cells, and limited solely to glial cells including
foetal oligodendrocytes, which were previously not suspected to be involved in MT
physiology. Distinctive shifts in the regional and cell-type expression of MT were
observed during neural development, and these are discussed in terms of the
functional role of MT.
The expression of MT-III, the brain specific isoform, is of current interest.
This thesis reports the cloning of the gene encoding this isoform from a sheep brain
cDNA library. Although homologous to MT-III isoforms from other species, the
predicted sheep MT-III protein sequence contains several unique features, including
the deletion of a highly conserved 3 amino acid sequence, and thus may have altered
metal binding properties. Sheep MT-III mRNA was shown to follow the same
regional and developmental expression patterns as MT-I and -II mRNA. This unique
MT-III isoform may be useful to resolve pending questions about the role of MT-III
in the brain, and the apparent neurotrophic actions of this isoform.
This work also investigates a novel human MT isogene, MTIL, which contains
a TGA ("stop") codon midway through the transcribed region. By analogy to previously characterised human MT genes, this codon interrupts the putative coding
region of MTIL, suggesting the isogene is either not functional, expresses a truncated
protein or potentially, produces a novel selenoprotein. In previous work, the author
has shown that the gene has biological activity since it can confer resistance to
cadmium to a transfected cell line. In this thesis, MTIL was shown to produce a full
length mRNA transcript when cloned into expression vectors, and furthermore
expression of MTIL mRNA was detected in a range of endocrine tissues and
lymphocytes by northern blotting and RT-PCR. These findings confirm that MTIL
has the potential to contribute to the repertoire of MT expression in the human.

Item Type: Thesis - PhD
Authors/Creators:Holloway, AF
Keywords: Metallothionein
Copyright Holders: The Author
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Copyright 1996 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
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Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1997. Includes bibliographical references. Contents: Expression of MT-I and -II isoforms in the developing sheep brain -- Cloning of the sheep MT-III CDNA -- Expression of the human MT1L gene

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