Retinoic acid down-regulates the expression of EmH-3 homeobox-containing gene in the freshwater sponge Ephydatia muelleri.
The effects of retinoic acid (RA), a common morphogen and gene expression regulator in vertebrates, were studied in the freshwater sponge Ephydatia muelleri, both on morphogenesis and on the expression of EmH-3 homeobox-containing gene. At 0.3 microM, RA had no noticeable influence on sponge development, slightly up-regulating EmH-3 expression. In contrast, in sponges reared in 10, 8 microM and to a lesser extent 2 microM RA, there was a strong down-regulation of EmH-3 expression after hatching. This induced modifications in cell composition and morphology, greatly disturbing normal development. Archaeocytes kept the features found in newly hatched sponges while choanocytes and a functional aquiferous system were completely absent. The inhibition of morphogenesis and down-regulation of EmH-3 expression were reversible when sponges were no longer subjected to RA. After RA removal, EmH-3 expression returned to the high values found in untreated sponges, archaeocytes differentiated into choanocytes and sponges achieved a normal development. These results clearly show that, in freshwater sponges, the most primitive metazoan, RA may also act as a morphogen, regulating the expression of a homeobox-containing gene. They demonstrate that the expression of EmH-3 is necessary for the differentiation of archaeocytes into choanocytes and hence for the formation of a complete functional aquiferous system.
Nikko
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E
Laboratoire de Physiologie Cellulaire, Institut de Biologie et de Médecine Moléculaires, Université Libre de Bruxelles, CP 300, Rue des professeurs Jeener et Brachet 12, B-6041 Gosselies, Belgium. enikko@dbm.ulb.ac.be
Van de Vyver
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G
Richelle-Maurer
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E
D000818:Animals; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects*; D005618:Fresh Water; D005801:Genes, Homeobox / Q000187:drug effects*; D018398:Homeodomain Proteins / Q000235:genetics*; D011161:Porifera / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development; D014212:Tretinoin / Q000494:pharmacology*
C116345:EmH-3 protein, Ephydatia muelleri; D018398:Homeodomain Proteins; D014212:Tretinoin