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First published online 14 January 2009
doi: 10.1242/dev.029959

Development 136, 541-549 (2009)
Published by The Company of Biologists 2009
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Two ParaHox genes, SpLox and SpCdx, interact to partition the posterior endoderm in the formation of a functional gut

Alison G. Cole1,*, Francesca Rizzo1,*, Pedro Martinez2, Montserrat Fernandez-Serra1 and Maria I. Arnone1,{dagger}

1 Stazione Zoologica Anton Dohrn di Napoli, Villa Comunale, 80121 Napoli, Italy.
2 Department de Genètica, Universitat de Barcelona, Avenida Diagonal, 645, 08028 Barcelona, Spain.

{dagger} Author for correspondence (e-mail: miarnone{at}szn.it)

Accepted 9 December 2008

We report the characterization of the ortholog of the Xenopus XlHbox8 ParaHox gene from the sea urchin Strongylocentrotus purpuratus, SpLox. It is expressed during embryogenesis, first appearing at late gastrulation in the posterior-most region of the endodermal tube, becoming progressively restricted to the constriction between the mid- and hindgut. The physiological effects of the absence of the activity of this gene have been analyzed through knockdown experiments using gene-specific morpholino antisense oligonucleotides. We show that blocking the translation of the SpLox mRNA reduces the capacity of the digestive tract to process food, as well as eliminating the morphological constriction normally present between the mid- and hindgut. Genetic interactions of the SpLox gene are revealed by the analysis of the expression of a set of genes involved in endoderm specification. Two such interactions have been analyzed in more detail: one involving the midgut marker gene Endo16, and another involving the other endodermally expressed ParaHox gene, SpCdx. We find that SpLox is able to bind Endo16 cis-regulatory DNA, suggesting direct repression of Endo16 expression in presumptive hindgut territories. More significantly, we provide the first evidence of interaction between ParaHox genes in establishing hindgut identity, and present a model of gene regulation involving a negative-feedback loop.

Key words: Strongylocentrotus purpuratus, QPCR, Endomesoderm, Sea urchin larval development, Hindgut specification, GRN, Triple in situ hybridization


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