Zebrafish and fly Nkx6 proteins have similar CNS expression patterns and regulate motoneuron formation

Abstract

Genes belonging to the Nkx, Gsh and Msx families are expressed in similar dorsovental spatial domains of the insect and vertebrate central nervous system (CNS), suggesting the bilaterian ancestor used this genetic program during CNS development. We have investigated the significance of these similar expression patterns by testing whether Nkx6 proteins expressed in ventral CNS of zebrafish and flies have similar functions. In zebrafish, Nkx6.1 is expressed in early-born primary and later-born secondary motoneurons. In the absence of Nkx6.1, there are fewer secondary motoneurons and supernumerary ventral interneurons, suggesting Nkx6.1 promotes motoneuron and suppresses interneuron formation. Overexpression of fish or fly Nkx6 is sufficient to generate supernumerary motoneurons in both zebrafish and flies. These results suggest that one ancestral function of Nkx6 proteins was to promote motoneuron development.

Regulation and function of Dbx genes in the zebrafish spinal cord

“…Consistent with previous studies, expression of nkx6.1 (Fig. 3C,CЈ ;Cheesman et al, 2004) and nkx6.2 ( Fig. 3E,EЈ; Guner and Karlstrom, 2007) were abolished in embryos treated with cyclopamine at 50% epiboly, whereas dimethyl sulfoxide (DMSO) -treated embryos displayed normal expression of these markers.…”

“…In fact, sequence comparison between the three genes indicates dbx2 is the most divergent (Seo et al, 1999). Recent reports in zebrafish have shown that many of the spinal progenitor genes have conserved spatial relationships (Cheesman et al, 2004;Lewis et al, 2005;Guner and Karlstrom, 2007). We have demonstrated that the relationship of Dbx expression to other progenitor genes is evolutionarily conserved in zebrafish, which we find intriguing given the size difference of the zebrafish spinal cord compared with amniotes.…”

“…The following RNA probes were made by our lab from DNA plasmids: dbx1a, dbx1b, dbx2, msxc, and nkx6.2. We were given the following DNA plasmids: en1b (Higashijima et al, 2004), krox20 (Oxtoby and Jowett, 1993), nkx2.2 (Barth and Wilson, 1995), nkx6.1 (Cheesman et al, 2004), pax2.1 (Krauss et al, 1991), pax3 (Seo et al, 1998), pax7 (Seo et al, 1998), ptc1 (Concordet et al, 1996), and olig2 (Park et al, 2002). For whole-mount photography after all staining methods, embryos were deyolked and mounted laterally or crosssectioned on a cryostat.…”

Acetyl l-carnitine protects motor neurons and Rohon-Beard sensory neurons against ketamine-induced neurotoxicity in zebrafish embryos

“…The transcription factor hb9 is found in developing motor neurons of both mammals (William et al, 2003) and zebrafish (Cheesman et al, 2004;Park et al, 2004). In the hb9-GFP transgenic fish, motor neurons are labeled with strong neuron-specific expression of GFP under the control of the regulatory elements of the zebrafish hb9 gene (Flanagan-Steet et al, 2005;Nakano et al, 2005).…”

“…Importantly, in another study we also showed that acetyl L-carnitine counteracts ketamine's negative effects on heart rate and ERK (MAPK) activity in zebrafish embryos (Kanungo et al, 2012). In order to quantitate the effect of ketamine on motor neurons in vivo, hb9:green fluorescent protein (hb9:GFP) transgenic zebrafish embryos were used, in which the promoter of the transcription factor hb9 that is found in developing motor neurons of both mammals (William et al, 2003) and zebrafish (Cheesman et al, 2004;Park et al, 2004), drives GFP expression specifically in motor neurons (Flanagan-Steet et al, 2005;Nakano et al, 2005).…”