Intestine in the lung

[moderator's note: This gets my vote for ickiest title so far.
Sounds like the aftermath of a (American) football game. - JAH]

Jonathan MW Slac

Abstract

The phenomenon of metaplasia, in which one tissue type is converted into
another, is beginning to be explained in molecular terms. The transformation
of lung to intestinal tissue has not previously been described, but it is
now reported that it can be brought about by prolonged Wnt signaling in late
development.

The transformation of one tissue type to another, a process called
metaplasia, is a fascinating aspect of both pathology and developmental
biology. Metaplasias represent the homeotic transformations of vertebrates,
comparable to the homeotic mutations in Drosophila that can transform
antenna to leg or wing to haltere [1]. Of particular developmental interest
are cases where tissues are transformed to other types that normally occur
elsewhere in the body, as for example in the formation of intestinal tissue
from the esophageal epithelium in the condition known as Barrett's esophagus
[2].

Both the intestine and the esophagus arise from the endoderm of land
vertebrates, which starts out as a simple sheet, or tube, of cells that
becomes a series of epithelial tissue types; these are, arranged roughly
from cranial to caudal: esophagus, trachea, bronchi, lungs, stomach, liver,
pancreas, small intestine, and colon. These epithelia arise in different
places because of distinct inductive signals from the mesoderm that is
associated with the endoderm in different locations [3]. (The endoderm and
mesoderm are the inner and middle two, respectively, of the three original
cellular layers of the vertebrate embryo from which the adult tissues
arise.) The ultimate source of the positional information in the mesoderm
may be the pattern of expression of Hox genes, which is set up in early
development, but this is not yet certain [4].

It has become a well-established principle of developmental biology that the
identity of a tissue type is specified by the combination of transcription
factors activated during embryonic development. Only a small subset of
transcription factors is involved in this process, acting combinatorially to
form developmental 'codes' that correspond to particular tissue types. If
the genes encoding these factors are turned on or off inappropriately then
the code is changed to that for a different tissue type and a homeotic
transformation results [5]. These genes are thus the ones usually described
as homeotic genes, or selector genes or master regulator genes (depending on
the organism of interest). For the endoderm-derived epithelia, each homeotic
gene is normally active in only one region, so there is a correspondence
between epithelial tissue type and body part, and the similarity between
metaplasias and homeosis in Drosophila is quite clear-cut.

Read the rest at the Journal of Biology
http://jbiol.com/content/3/3/10
(Requires free registration)

Posted by
Robert Karl Stonjek.
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