TEMPORAL AND SPATIAL EXPRESSION OF AN INTESTINAL NA+ PO43- COTRANSPORTER CORRELATES WITH EPITHELIAL TRANSFORMATION DURING THYROID HORMONE-DEPENDENT FROG METAMORPHOSIS/
A. Ishizuyaoka et al., TEMPORAL AND SPATIAL EXPRESSION OF AN INTESTINAL NA+ PO43- COTRANSPORTER CORRELATES WITH EPITHELIAL TRANSFORMATION DURING THYROID HORMONE-DEPENDENT FROG METAMORPHOSIS/, Developmental genetics, 20(1), 1997, pp. 53-66
The amphibian intestine has two morphologically distinct structures du
ring development. Early embryogenesis generates a simple, tubelike int
estine in the tadpole whereas after thyroid hormone (T-3)-dependent me
tamorphosis a newly remodeled adult intestine is formed similar to tha
t of higher vertebrates. This change requires a drastic transformation
of the epithelial layer. We have isolated a Na+/PO43- cotransporter g
ene that may contribute to this transformation. The deduced amino acid
sequence of this gene shows a high degree of homology to the mammalia
n renal Na+/PO43- cotransporters, which have little or no expression i
n organs other than the kidney. The frog gene is highly expressed and
regulated by T-3 in the intestine with lithe expression and/or regulat
ion by T-3 in most other organs. Its mRNA is restricted to the differe
ntiated epithelial cells both in tadpoles and postmetamorphic frogs. I
nterestingly, its expression is low in premetamorphic tadpoles, but up
-regulated when metamorphosis is initiated by endogenous T-3. As the l
arval epithelium undergoes programmed cell death (apoptosis), the mRNA
level drops to a minimum. Subsequently the gene is reactivated at the
tip region of the newly formed adult intestinal folds and a crest-tro
ugh polarity of expression is established by the end of metamorphosis.
This temporal regulation profile is also reproduced when premetamorph
ic tadpoles are treated with T-3 to induce precocious intestinal remod
eling. These results suggest a possible role of the Na+/PO43- cotransp
orter during metamorphosis and demonstrate that the adult epithelial c
ell differentiation pattern is established in the direction of crest-t
o-trough of the intestinal fold, concurrent with the epithelial morpho
genic process. (C) 1997 Wiley-Liss, Inc.