Conserved anterior boundaries of Hox gene expression in the central nervous system of the leech Helobdella


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Conserved anterior boundaries of Hox gene expression in the central nervous system of the leech Helobdella
Developmental Biology
Kourakis  M. J., Master  V. A., Lokhorst  D. K., Nardelli-Haefliger  D., Wedeen  C. J., Martindale  M. Q., Shankland  M.
0012-1606 (Print)
Statut éditorial
Date de publication
Journal Article
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.
Research Support, U.S. Gov't, P.H.S. --- Old month value: Oct 15
Molecular developmental studies of fly and mouse embryos have shown that the identity of individual body segments is controlled by a suite of homeobox-containing genes called the Hox cluster. To examine the conservation of this patterning mechanism in other segmented phyla, we here describe four Hox gene homologs isolated from glossiphoniid leeches of the genus Helobdella. Based on sequence similarity and phylogenetic analysis, the leech genes Lox7, Lox6, Lox20, and Lox5 are deemed to be orthologs of the Drosophila genes lab, Dfd, Scr, and Antp, respectively. Sequence similarities between Lox5 and Antp outside the homeodomain and phylogenetic reconstructions suggest that the Antennapedia family of Hox genes (as defined by Burglin, 1994) had already expanded to include at least two discrete Antp and Ubx/abdA precursors prior to the annelid/arthropod divergence. In situ hybridization reveals that the four Lox genes described in this study are all expressed at high levels within the segmented portion of the central nervous system (CNS), with variable levels of expression in the segmental mesoderm. Little or no expression was seen in peripheral ectoderm or endoderm, or in the unsegmented head region (prostomium). Each Lox gene has a distinct anterior expression boundary within one of the four rostral segments, and the anterior-posterior (AP) order of these expression boundaries is identical to that reported for the orthologous Hox gene products in fly and mouse. This finding supports the idea that the process of AP axis differentiation is conserved among the higher metazoan phyla with respect to the regional expression of individual Hox genes along that axis. One unusual feature of leech Hox genes is the observation that some genes are only expressed during later development -- beginning at the time of terminal cell differentiation -- whereas others begin expression at a much earlier stage, and their RNA ceases to be detectable shortly after the onset of expression of the 'late' Hox genes. The functional significance of this temporal disparity is unknown, but it is noteworthy that only the two 'early' Hox genes display high levels of mesodermal expression.
Amino Acid Sequence Animals Annelida/genetics Antennapedia Homeodomain Protein Arthropods/genetics Base Sequence Body Patterning Conserved Sequence Drosophila/genetics *Drosophila Proteins Embryo, Nonmammalian/anatomy & histology Evolution, Molecular Gene Expression *Genes, Homeobox Homeodomain Proteins/genetics Insect Proteins/genetics Leeches/*genetics Lipoxygenase/genetics Models, Genetic Molecular Sequence Data Nerve Tissue Proteins/genetics Nervous System/*embryology *Nuclear Proteins Phylogeny Plant Proteins/genetics Sequence Analysis, DNA Sequence Homology, Amino Acid Tissue Distribution Transcription Factors/genetics
Web of science
Open Access
Création de la notice
25/01/2008 15:35
Dernière modification de la notice
20/08/2019 16:10
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