The Effects of Mutations in Hoxa13a, Hoxa13b, and hHoxd13a on the Zebrafish Fins

Teleosts, or ray-finned fish, are the largest and most diverse class of vertebrates in the world. Among this diversity includes many differences in fin structure. Zebrafish typically have only soft rays in their fins, while acanthomorph fish have both soft and spiny rays in select fins. How this difference between fin elements arose remains an unanswered question in evolutionary biology, although hox gene expression patterns could play a prominent role in this evolutionary event. Hox genes encode transcription factors that are important for patterning during development. Specifically, the hox13 genes have been shown to be essential for proper limb and fin patterning and are expressed only in soft rays and not spiny rays during acanthomorph fin development. Hoxa13 -/-, Hoxd13 -/- mice completely lack the autopod in their developing limbs. The function of the fish orthologs hoxa13a, hoxa13b, and hoxd13a are not as well defined in fin ray development, although clear structural changes to the fin rays such as truncations and loss of joints, bifurcations and actinotrichia can be seen in the absence of these genes. In this project, various zebrafish compound mutants for hoxa13a, hoxa13b, and hoxd13a are compared to gain insight into the individual roles of each hox13 gene during fin development. From these observations, hoxa13a and hoxa13b appear to have a more prominent role in fin ray patterning, and only require one copy to produce joints, bifurcations and actinotrichia in the rays of every fin. Hoxd13a however requires two copies to perform a similar function. After generating and observing triple hox13 mutant zebrafish, a comparison between these mutant rays and acanthomorph spines was performed using micro-CT scanning and in situ hybridization. Triple hox13 mutant fin rays were found to have highly ossified fin rays as seen in spines, as well as proportionally increased expression of the spine marker alx4a during early development. All in all, the triple hox13 mutant rays appear to be forming an intermediate structure between soft rays and spiny rays, highlighting the potential impact of hox13 downregulation in the evolution of acanthomorph spines.

Grantor dc:publisher

Université d'Ottawa / University of Ottawa

Year dc:date

2023

Author dc:creator

• Corcoran, Jordan

Contributors dc:contributor

• Akimenko, Marie-Andrée

• Zebrafish

Language dc:language

en

Identifier

http://dx.doi.org/10.20381/ruor-29370

OAI identifier oai:identifier

oai:ruor.uottawa.ca:10393/45164