Functional Repression of Islet-2 by Disruption of Complex with Ldb Impairs Peripheral Axonal Outgrowth in Embryonic Zebrafish

Abstract

Islet-2 is a LIM/homeodomain-type transcription factor of the Islet-1 family expressed in embryonic zebrafish. Two Islet-2 molecules bind to the LIM domain binding protein (Ldb) dimers. Overexpression of the LIM domains of Islet-2 or the LIM-interacting domain of Ldb proteins prevented binding of Islet-2 to Ldb proteins in vitro and caused similar in vivo defects in positioning, peripheral axonal outgrowth, and neurotransmitter expression by the Islet-2-positive primary sensory and motor neurons as the defects induced by injection of Islet-2-specific antisense morpholino oligonucleotide. These and other experiments, i.e., mosaic analysis, coexpression of full-length Islet-2, and overexpression of the chimeric LIM domains derived from two different Islet-1 family members, demonstrated that Islet-2 regulates neuronal differentiation by forming a complex with Ldb dimers and possibly with some other Islet-2-specific cofactors.

hgf/c‐met expression and functional analysis during zebrafish embryogenesis

“…To confirm the identity of c-met-expressing cells within the neural tube, we performed double in situ hybridization using a digoxigenin-labeled c-met probe and a fluorescein-labeled isl2 probe, a marker for both CaP and VaP motor neurons, which have an equivalent development potential (Eisen, 1992). Our results confirm previous studies (Segawa et al, 2001;Tallafuss and Eisen, 2008) showing that c-met and isl2 RNA probes label the same cells (Fig. 3D,E).…”

“…Previous work has documented zebrafish c-met expression in tissues necessary for formation and development of muscle and the posterior lateral line (Haines et al, 2004), spinal cord motor neurons (Segawa et al, 2001;Tallafuss and Eisen, 2008), and inferior and superior extraocular muscles (Lin et al, 2006). c-met expression (using a 496-bp probe, GenBank CK690356) has also been described as part of a large-scale in situ hybridization screen directly submitted to the Zebrafish Information Network ; http://zfin.org).…”

“…Furthermore, this work showed that Met is necessary for deposition of pro-neuromasts by the migrating posterior lateral line primordia. Spinal cord CaP, VaP, MiP, and RoP primary motor neurons and many secondary motor neurons express c-met (Segawa et al, 2001;Tallafuss and Eisen, 2008), and Met is required for secondary motor neuron formation and proper primary motor neuron axon development (Tallafuss and Eisen, 2008).…”

High-efficiency motor neuron differentiation from human pluripotent stem cells and the function of Islet-1

“…ISL1 is immediately expressed in prospective MNs when they exit cell cycle, and ISL1 deletion or hypomorphic mutations lead to the loss of spinal MN populations and conversion to Chx10-positive V2a interneurons in mice [12][13][14] , suggesting that ISL1 functions to maintain MN identity against interneurons. Islet is also required for axon projection and neurotransmitter expression of MNs in Drosophila 38 and zebrafish 39 . Despite these findings, ISL1 function has not been defined in human-based neural development models.…”

Nicotinic Receptors Mediate Changes in Spinal Motoneuron Development and Axonal Pathfinding in Embryonic Zebrafish Exposed to Nicotine

“…A fragment of the islet-1 promoter constitutively drives the GFP expression in these embryos (Higashijima et al, 2000). This transgenic line has been used recently to characterize the axonal branching patterns of motoneurons and also to characterize neuromuscular development in embryonic and larval zebrafish (Higashijima et al, 2000;Ono et al, 2001;Segawa et al, 2001). It is known that GFP expression is confined to a subclass of secondary motoneurons (Higashijima et al, 2000) in embryos older than 3 d postfertilization.…”