Meeting Abstract
Limb and digit formation provide an important system for studying the mechanisms of molecular patterning and morphogenesis during development. Members of the LIM-homeobox (Lhx) and Paired-homeobox (Pax) families of transcription factors have been shown to mediate essential signaling interactions during limb bud development in amniotes, and when experimentally inactivated result in dramatic abnormal phenotypes. For example, knockout studies in mice demonstrate that in the absence of functional Lhx2 and Lhx9, or the LIM-HD cofactor Ldb1, the zeugopod is greatly reduced and the autopod lacks a normal complement of digits. Likewise, mice deficient for Pax9 exhibit preaxial digit duplications in both fore- and hindlimbs, along with other defects in the developing autopod. The conserved patterning roles of Lhx and Pax genes in other organ systems (e.g. nervous system and tooth development, respectively) begs the question as to the ancestral role of these genes in paired appendage development prior to the origin of the autopod. Here we present transcriptome and gene expression data for paired fin development in the American paddlefish Polyodon spathula, a basal actinopterygian. Specifically, we compare the expression profiles of the LIM-homeobox genes Lhx2, Lhx9, and Lmx1b, and the Paired-homeobox gene Pax9, with other genes previously described for their role in fin compartmentalization. These data will inform our understanding of fin patterning in actinopterygians, and when placed in a comparative context fuel new hypotheses on how the gene regulatory networks underlying appendage development may have been altered during the fin to limb transition and the origin of digits.
