Touchtone promotes survival of embryonic melanophores in zebrafish

Abstract

An outstanding problem in the study of vertebrate development is the identification of the genes that direct neural crest precursor cells to adopt and maintain specific differentiated cell fates. In an effort to identify such genes, we have carried out a mutagenesis screen in zebrafish and isolated mutants that lack neural crest-derived melanophores. In this manuscript we describe the phenotype of one such mutant, touchtone(b722) (tct), and the map position of the gene it defines. Analysis of expression of dopachrome tautomerase (dct) and microphthalmia (mitfa) suggests that melanophore precursors are specified normally in homozygous tct mutants. However, differentiated melanophores are pale, small, and about half of them have disappeared by 48 h of development, apparently by cell death. We show that melanophores require Tct function cell autonomously. Signals from the receptor tyrosine kinase receptor C-kit are essential for survival of melanophores in zebrafish and mammals. However, differences in the phenotypes of tct and c-kit homozygous mutants, and an absence of interaction between c-kit and tct heterozygotes, suggest that Tct functions independently of the C-kit pathway. Other neural crest derivatives, including other pigment cell types, appear normal in tct mutants. Interestingly, tct mutant embryos undergo a temporary period of near complete paralyzis during the second day of development, although markers of axons of motor and sensory neurons look normal in this period. A fraction of tct(b722) mutants survive to adulthood, but mutant adults are small, indicating a role for Tct in post-larval growth. The tct gene maps to a small interval near a telomere of chromosome 18. Thus, we have identified a zebrafish gene that when mutated produces semi-viable offspring and that may serve as a model of human diseases that have both pigmentation and neurological symptoms.

Sorting out Sox10 functions in neural crest development

“…Likewise, apoptotic death of pigment cell progenitors may also be a result of the absence of Kit, or other survival factors for melanoblasts like Bcl and trpm7. (78,(81)(82)(83)(84) Finally, defects in melanocyte differentiation are easily explained since Mitf drives expression of all key melanogenic enzymes (reviewed in Ref. 62).…”

Abnormal differentiation of dopaminergic neurons in zebrafish trpm7 mutant larvae impairs development of the motor pattern

“…Independent screens for mutations that disrupt melanophore development, early motility, or adult growth each identified trpm7 mutants (Arduini and Henion, 2004; Cornell et al, 2004; Elizondo et al, 2005; Kelsh et al, 1996; Low et al, 2011). In trpm7 loss-of-function mutants, embryonic melanophores (the melanin-producing cells of fish) succumb to cell death (Arduini and Henion, 2004; Cornell et al, 2004), and the melanosomes (the organelles that confine melanin) are structurally abnormal (McNeill et al, 2007).…”

“…Independent screens for mutations that disrupt melanophore development, early motility, or adult growth each identified trpm7 mutants (Arduini and Henion, 2004; Cornell et al, 2004; Elizondo et al, 2005; Kelsh et al, 1996; Low et al, 2011). In trpm7 loss-of-function mutants, embryonic melanophores (the melanin-producing cells of fish) succumb to cell death (Arduini and Henion, 2004; Cornell et al, 2004), and the melanosomes (the organelles that confine melanin) are structurally abnormal (McNeill et al, 2007). Because Trpm7 is required within melanophores (Arduini and Henion, 2004; Cornell et al, 2004), the melanophore cell-death in trpm7 mutants may result from the release of toxic intermediates of melanin synthesis into the cytoplasm (Hochstein and Cohen, 1963; McNeill et al, 2007; Pawelek and Lerner, 1977).…”

“…In trpm7 loss-of-function mutants, embryonic melanophores (the melanin-producing cells of fish) succumb to cell death (Arduini and Henion, 2004; Cornell et al, 2004), and the melanosomes (the organelles that confine melanin) are structurally abnormal (McNeill et al, 2007). Because Trpm7 is required within melanophores (Arduini and Henion, 2004; Cornell et al, 2004), the melanophore cell-death in trpm7 mutants may result from the release of toxic intermediates of melanin synthesis into the cytoplasm (Hochstein and Cohen, 1963; McNeill et al, 2007; Pawelek and Lerner, 1977). Additionally, trpm7 mutant larvae are unresponsive to touch for a period of about 12 hrs during development (Arduini and Henion, 2004; Cornell et al, 2004; Kelsh et al, 1996; Low et al, 2011).…”

“…Because Trpm7 is required within melanophores (Arduini and Henion, 2004; Cornell et al, 2004), the melanophore cell-death in trpm7 mutants may result from the release of toxic intermediates of melanin synthesis into the cytoplasm (Hochstein and Cohen, 1963; McNeill et al, 2007; Pawelek and Lerner, 1977). Additionally, trpm7 mutant larvae are unresponsive to touch for a period of about 12 hrs during development (Arduini and Henion, 2004; Cornell et al, 2004; Kelsh et al, 1996; Low et al, 2011). This phenotype can be alleviated by forcing the expression of trpm7 in primary sensory neurons, implying that Trpm7 is required transiently for function or differentiation of embryonic primary sensory neurons (Low et al, 2011).…”