Abstract
Abstract
Background
Pharyngeal pouch formation is fundamental to vertebrate craniofacial development, but molecular mechanisms underlying posterior pouch formation remain incompletely understood. Retinoic acid (RA) signaling is required for posterior pharyngeal development, and Hox genes are established RA targets. However, their genetic requirement in posterior pouch formation has not been established.
Results
Zebrafish lacking both
hoxba
and
hoxbb
clusters—teleost‐specific duplicates of the ancestral HoxB cluster—exhibited severe loss of posterior pharyngeal pouches and associated pharyngeal skeletal elements, accompanied by reduced expression of the pouch marker
pax1a
. Alcian blue analysis revealed highly similar losses of posterior pharyngeal skeletal elements in
hoxba;hoxbb
and RA‐deficient
aldh1a2
mutants. Pharyngeal expression of
hoxb1a
and
hoxb1b
was reduced in
aldh1a2
mutants. Combined knockdown of
hoxb1a
and
hoxb1b
caused variable, incompletely penetrant posterior pouch abnormalities, supporting their contribution to HoxB‐cluster function.
Conclusions
These results provide genetic evidence that the
hoxba
and
hoxbb
clusters are redundantly required for posterior pharyngeal pouch development. The highly similar posterior pharyngeal abnormalities in
hoxba;hoxbb
and
aldh1a2
mutants, together with reduced
hoxb1a
and
hoxb1b
expression, support a functional association between RA signaling and HoxB‐cluster activity. Together, these findings identify the duplicated HoxB‐derived clusters as important genetic components of RA‐associated posterior pharyngeal development.