Hox gene expression patterns in Lethenteron japonicum embryos--insights into the evolution of the vertebrate Hox code.
The Hox code of jawed vertebrates is characterized by the colinear and rostrocaudally nested expression of Hox genes in pharyngeal arches, hindbrain, somites, and limb/fin buds. To gain insights into the evolutionary path leading to the gnathostome Hox code, we have systematically analyzed the expression pattern of the Hox gene complement in an agnathan species, Lethenteron japonicum (Lj). We have isolated 15 LjHox genes and assigned them to paralogue groups (PG) 1-11, based on their deduced amino acid sequences. LjHox expression during development displayed gnathostome-like spatial patterns with respect to the PG numbers. Specifically, lamprey PG1-3 showed homologous expression patterns in the rostral hindbrain and pharyngeal arches to their gnathostome counterparts. Moreover, PG9-11 genes were expressed specifically in the tailbud, implying its posteriorizing activity as those in gnathostomes. We conclude that these gnathostome-like colinear spatial patterns of LjHox gene expression can be regarded as one of the features already established in the common ancestor of living vertebrates. In contrast, we did not find evidence for temporal colinearity in the onset of LjHox expression. The genomic and developmental characteristics of Hox genes from different chordate species are also compared, focusing on evolution of the complex body plan of vertebrates.
Takio
Yoko
Y
RIKEN Center for Developmental Biology, Evolutionary Morphology Research Group, 2-2-3 Minatojima Minamimachi, Chuo-ku, Kobe 650-0047, Japan.
Kuraku
Shigehiro
S
Murakami
Yasunori
Y
Pasqualetti
Massimo
M
Rijli
Filippo M
FM
Narita
Yuichi
Y
Kuratani
Shigeru
S
Kusakabe
Rie
R
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001934:Branchial Region / Q000196:embryology; D043344:Chordata / Q000196:embryology / Q000235:genetics; D017931:DNA Primers / Q000235:genetics; D019143:Evolution, Molecular; D005260:Female; D018507:Gene Expression Regulation, Developmental; D005801:Genes, Homeobox; D018398:Homeodomain Proteins / Q000235:genetics; D007568:Jaw / Q000196:embryology; D007798:Lampreys / Q000196:embryology* / Q000235:genetics*; D008297:Male; D008969:Molecular Sequence Data; D009420:Nervous System / Q000196:embryology; D012249:Rhombencephalon / Q000196:embryology; D017386:Sequence Homology, Amino Acid; D013623:Tail / Q000196:embryology; D014714:Vertebrates / Q000196:embryology / Q000235:genetics
D017931:DNA Primers; D018398:Homeodomain Proteins