Meeting Abstract
Comparisons of fish fins with tetrapod limbs have been limited by a relative lack of understanding of the cellular and molecular processes underlying the development of the fin skeleton. For example, knockout and cell lineage data of genes essential for patterning skeletal structures in mice have been lacking for orthologous genes in fish. Here, we provide the first functional analysis, using CRISPR/Cas9 and fate mapping, of 5’ hox genes and enhancers in zebrafish that are indispensable for the development of the segments of endochondral bones of tetrapod limbs. We show that the fates of cells marked by the activity of an autodial hoxa13 enhancer exclusively form elements of the fin fold including the osteoblasts of the dermal rays. Moreover, in hox13 knockout fish, we find a dramatic reduction and loss of fin rays that is associated with an increased number of endochondral distal radials. Our data reveal a developmental connection between the fin rays and digits of tetrapods, and suggest a mechanism of endochondral expansion in tetrapod origins by via the transition of distal cellular fates.
