Dg. Ahn et G. Gibson, Expression patterns of threespine stickleback Hox genes and insights into the evolution of the vertebrate body axis, DEV GENES E, 209(8), 1999, pp. 482-494
Understanding the patterning mechanisms that operate to promote differentia
tion of individual segments along the main body axis is an important goal o
f both developmental and evolutionary biology. In order to gain a better in
sight into the role of Hox genes in generating diversity of axial plans see
n in vertebrates, we have cloned 11 homeobox sequences from an acanthoptery
gian teleost, the threespine stickleback, and analyzed the expression of 7
of thee during embryogenesis. Transcripts are observed in a variety of tiss
ues including thp neural tube paraxial mesoderm, lateral plate mesoderm, pe
ctoral fins, pronephric ducts, as well as some neural crest-derived structu
res. Anterior limits of expression in the central nervous system and paraxi
al mesoderm exhibited both similarities and differences to those of mouse a
nd zebrafish homologs. In both stickleback and zebrafish embryos expression
limits within the paraxial mesoderm were detected only within the trunk re
gion in which ribs are attached to all vertebrae. The finding of this patte
rn in two divergent teleosts as well as in various tetrapod species support
s the hypothesis that a Hox precede was present prior to the divergence of
ray-finned and lobe-finned fishes and was subsequently used to generate dif
ferent types of vertebrae in tetrapods. We also describe a dynamic pattern
of expression of several stickleback Hox genes associated with the developm
ent of the caudal paraxial mesoderm, which suggests uncoupling of the proce
ss of segmentation from segmental identity determination. We propose that i
n fishes the patterning of the tail region is under the control of a separa
te mechanism from the trunk, which utilizes Hox genes in a different manner
.