Leukocyte Tyrosine Kinase Functions in Pigment Cell Development

Abstract

A fundamental problem in developmental biology concerns how multipotent precursors choose specific fates. Neural crest cells (NCCs) are multipotent, yet the mechanisms driving specific fate choices remain incompletely understood. Sox10 is required for specification of neural cells and melanocytes from NCCs. Like sox10 mutants, zebrafish shady mutants lack iridophores; we have proposed that sox10 and shady are required for iridophore specification from NCCs. We show using diverse approaches that shady encodes zebrafish leukocyte tyrosine kinase (Ltk). Cell transplantation studies show that Ltk acts cell-autonomously within the iridophore lineage. Consistent with this, ltk is expressed in a subset of NCCs, before becoming restricted to the iridophore lineage. Marker analysis reveals a primary defect in iridophore specification in ltk mutants. We saw no evidence for a fate-shift of neural crest cells into other pigment cell fates and some NCCs were subsequently lost by apoptosis. These features are also characteristic of the neural crest cell phenotype in sox10 mutants, leading us to examine iridophores in sox10 mutants. As expected, sox10 mutants largely lacked iridophore markers at late stages. In addition, sox10 mutants unexpectedly showed more ltk-expressing cells than wild-type siblings. These cells remained in a premigratory position and expressed sox10 but not the earliest neural crest markers and may represent multipotent, but partially-restricted, progenitors. In summary, we have discovered a novel signalling pathway in NCC development and demonstrate fate specification of iridophores as the first identified role for Ltk.

Genetic ablation of neural crest cell diversification

“…;tfap2a low double mutant embryos Analysis of the expression of genes required for and/or diagnostic of the specification of major NC sublineages prior to the overt differentiation of derivatives in foxd3 zdf10 ;tfap2a low double mutant embryos revealed a global failure in the initiation of NCC diversification ( (Lister et al, 1999), xdh (Budi et al, 2008), ltk (Lopes et al, 2008) and ednrb1 (Parichy et al, 2000) ( Fig. 2A-D (Allende and Weinberg, 1994;Lucas et al, 2006) (data not shown) fail to occur.…”

New Tools for the Identification of Developmentally Regulated Enhancer Regions in Embryonic and Adult Zebrafish

“…1C¢, 1C †). Iridescent iridophores, which are derivatives of the neural crest, 51 are reflective pigment cells present on the eye and, in line TDL358, they express GFP around the eye and operculum at 30 dpf (Fig. 1C, 1C¢).…”

Anaplastic lymphoma kinase activates the small GTPase Rap1 via the Rap1-specific GEF C3G in both neuroblastoma and PC12 cells

“…In the fruit fly ALK and Jeb are required for neuronal circuit assembly in the visual system, mediating correct targeting of photoreceptor axons (Bazigou et al, 2007), whereas ALK in C. elegans is expressed in motor neurons, where it is involved in the neuronal control of entry into dauer as well as synapse stabilization (Liao et al, 2004;Reiner et al, 2008). Furthermore, in the zebrafish model system it has been shown that LTK, which belongs to the LTK/ALK family, is expressed in developing neural crest cells and is important for the specification of iridophores from the neural crest linage (Lopes et al, 2008).…”