Elsevier

Developmental Biology

Volume 308, Issue 2, 15 August 2007, Pages 606-620
Developmental Biology

Genomes & Developmental Control
Hox gene expression patterns in Lethenteron japonicum embryos—Insights into the evolution of the vertebrate Hox code

https://doi.org/10.1016/j.ydbio.2007.05.009Get rights and content
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Abstract

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.

Keywords

Evolution
Hindbrain
Rhombomere
Pharyngeal arches
Neural crest
Lamprey
Hox
Tail bud

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