Biology Reference
In-Depth Information
either fail to be established or fail to be recruited. In these mutants, pigment
pattern metamorphosis is effectively decoupled from overall somatic meta-
morphosis (e.g.,
Budi et al., 2008; Larson et al., 2010; Parichy & Turner,
2003b
). Once latent precursors have been recruited, a variety of genes acting
both within the pigment cells and in the tissue environments through which
these cells migrate are required to organize the different pigment cell classes
into distinct juvenile and adult stripes (
Eom et al., 2012; Iwashita et al., 2006;
Lang et al., 2009; Parichy, Rawls, Pratt, Whitfield, & Johnson, 1999;
Parichy & Turner, 2003a; Watanabe et al., 2006
).
Phylogenetic comparisons reveal that adult pigment patterns of zebrafish
relatives similarly depend on the recruitment of latent pigment cell precur-
sors at metamorphosis. Interestingly, however, these cells have been mostly
lost in the closely related
Danio nigrofasciatus
, in which the adult pigment pat-
tern arises at metamorphosis largely through the rearrangement of embry-
onic/early larval melanophores that persist into the adult. Interspecific
cell transplantation shows that the difference in adult melanophore develop-
ment between zebrafish and
D. nigrofasciatus
lies extrinsic to the pigment
cells, implicating a change in a still-unidentified tissue or cell type that in-
fluences metamorphic processes within the pigment cell lineage (
Quigley
et al., 2004
). This example highlights the potential for comparative studies
to reveal the cellular, and ultimately genetic, bases underlying evolutionary
changes in metamorphic transformations.
In contrast to other teleosts, flatfish develop pigmentation in an asym-
metric manner at metamorphosis, with only the ocular (upper) side normally
developing adult melanophores. In flounder, pigment cell precursors
migrate symmetrically to both lateral sides from the bases of fins at the dorsal
and ventral margins of the flank, yet these cells differentiate as melanophores
only on the ocular side (
Watanabe et al., 2008; Yamada, Okauchi, & Araki,
2010
). The genetic bases for this differential response of pigment cells remain
unknown.
Development of metamorphic pigmentation in zebrafish is retarded by
goitrogens that prevent TH synthesis (
Brown, 1997
). Whether TH is
directly required by pigment cells or their precursors, or whether the hor-
mone exerts an influence indirectly through other cellular intermediaries, is
an active area of investigation. Treatment with high (hyper-physiological)
levels of T4 actually inhibits adult melanophore development in flatfish
(
Yoo et al., 2000
), eels (
Jegstrup & Rosenkilde, 2003
) and zebrafish
(D.M. Parichy, unpublished data), but the biological significance of these
observations remains obscure. Likewise, the genetic and cellular mechanisms
