Embryonic expression patterns of Hox genes in the oligochaete annelid Tubifex tubifex.
We have cloned and characterized the expression of seven Hox genes (designated Ttu-lab, Ttu-Dfd, Ttu-Scr1, Ttu-Scr2, Ttu-Lox5, Ttu-Lox4 and Ttu-Lox2) from the oligochaete annelid Tubifex tubifex. RT-PCR analyses show that except for Ttu-Lox4 and Ttu-Lox2 which begin expression as early as cleavage stages, Tubifex Hox genes are expressed during stages 13-18 when embryos undergo germ band formation, segmentation and body elongation. In terms of combination of tissues (or organs) exhibiting positive cells, the Tubifex Hox genes examined in this study are classified into three groups. Ttu-lab, Ttu-Scr1 and Ttu-Lox5 are expressed only in the ventral nerve cord; Ttu-Scr2 and Ttu-Lox4 are expressed not only in the ventral nerve cord but also in distinct lateral segmental tissues; and Ttu-Dfd and Ttu-Lox2 are expressed not only in the segmental ectoderm along the length of the AP body axis but also in the prostomium. Anterior expression boundaries of Ttu-lab, Ttu-Scr1, Ttu-Lox5 and Ttu-Lox4 are at segments 3, 4, 5, and 9, respectively. Anterior expression boundary of Ttu-Scr2 is at segment 2, and Ttu-Dfd and Ttu-Lox2 are expressed even at the anteriormost portion, the prostomium. These observations suggest that as in other annelids, so-called "spatial colinearity" of anterior expression boundaries of Hox genes has been conserved in the oligochaetes. It is also evident that there are some oligochaete Hox genes which violate the spatial colinearity rule.
Graduate School of Life Science, Hokkaido University, Sapporo 060-0810, Japan.
Mao
M
Endo
Graduate School of Life Science, Hokkaido University, Sapporo 060-0810, Japan.
Chiharu
C
Sakai
Graduate School of Life Science, Hokkaido University, Sapporo 060-0810, Japan; Department of Biological Sciences, Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan. Electronic address: stak@sci.hokudai.ac.jp.
Takashi
T
Shimizu
D000595:Amino Acid Sequence; D000818:Animals; D004475:Ectoderm / Q000254:growth & development / Q000378:metabolism; D004625:Embryo, Nonmammalian; D047108:Embryonic Development / Q000235:genetics*; D018507:Gene Expression Regulation, Developmental; D005801:Genes, Homeobox / Q000235:genetics*; D018398:Homeodomain Proteins / Q000096:biosynthesis* / Q000235:genetics; D009835:Oligochaeta / Q000235:genetics* / Q000254:growth & development; D010802:Phylogeny
D018398:Homeodomain Proteins
Annelids; Hox genes; Oligochaetes; Segments; Spatial colinearity; Tubifex tubifex