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Fig. 8. Altered melanophore lineage development in D. albolineatus. (A-H)
Melanophore precursor abundance does not differ dramatically between species
as revealed by distributions of cells expressing tyrosinase, dopachrome
tautomerase (dct) and mitfa
(Lister et al., 1999;
Kelsh et al., 2000;
Camp and Lardelli, 2001).
tyrosinase and dct encode enzymes required for melanin
synthesis, whereas mitfa encodes a transcription factor essential for
melanophore specification. (A-D) In situ hybridization for tyrosinase
mRNA in D. rerio (A,B) and D. albolineatus (C,D) during
middle stages of pigment pattern metamorphosis (equivalent to larvae shown in
Fig. 6C,I). (A) In D.
rerio, numerous tyrosinase+ melanophores and
unmelanized melanophore precursors (arrowhead) are observed in the region of
the prospective dorsal primary melanophore stripe. (B) Higher magnification
image of a different larvae showing tyrosinase+
melanophores (arrow) and melanophore precursors (arrowhead). (C) In D.
albolineatus, fewer melanophores are present but
tyrosinase+ melanophore precursors (arrowhead) are not
obviously reduced in number. (D) Higher magnification of a different larva
showing tyrosinase+ melanophores (arrowhead) and
unmelanized melanophore precursor (arrowhead). (E-H) Expression of other
melanophore lineage markers also is similar between D. rerio and
D. albolineatus. (E,F) Danio rerio exhibit unmelanized cells
(arrowheads), and some melanized cells (arrow) expressing dct (E) and
mitfa (F). (G,H) In D. albolineatus, the numbers of
unmelanized cells expressing dct (G) and mitfa are similar
to D. rerio. Results for kit and sox10-expressing
cells were similar (data not shown)
(Parichy et al., 1999;
Dutton et al., 2001). (I-L)
Tyrosinase-expressing melanophore precursors revealed by treating fixed larvae
with the essential precursor for melanin synthesis, L-dopa
(Camp and Lardelli, 2001;
McCauley et al., 2004). Images
in I and K are prior to L-dopa incubation, and images in J and L
are the same fields of view after treatment with L-dopa for 5
hours. (I,J) In D. rerio, only a few tyrosinase+
melanophore precursors are revealed by L-dopa incubation
(arrowheads). (K,L) In D. albolineatus, however, numerous
tyrosinase+ melanophore precursors are revealed by
L-dopa treatment (arrowheads show only a few of these cells). These
cells exhibit morphologies typical of melanoblasts and recently differentiated
melanophores (inset). The increased number of L-dopa stained,
tyrosinase+ cells as compared with molecular markers in D.
albolineatus may reflect perduring protein in the absence of
transcriptional activity. (M-T). Melanophores and melanophore precursors
frequently are lost in D. albolineatus. (M-O) The same region of a
D. albolineatus larvae imaged at 12-hour intervals reveals the
transient appearance of several melanophores (arrowheads). Yellow-orange cells
are xanthophores; these and other melanophores do not change positions between
images. (P) High magnification image of D. albolineatus reveals
melanin-containing debris (arrow) typical of melanophore death. Arrowhead,
melanophore precursor that acquired melanin following L-dopa
incubation of this larva. (Q-S) Cross-sections reveal the locations of
melanophores and tyrosinase+ melanophore precursors in D.
rerio (Q) and D. albolineatus (R,S). (Q) In D. rerio,
few melanophores or melanophore precursors are located within the plane of the
epidermis; one such melanophore is indicated by the arrowhead. e, epidermis;
m, myotome. Arrow indicates iridophores of the developing interstripe region.
(R) In D. albolineatus, numerous melanophores and
tyrosinase+ melanophore precursors occur within the plane of the
epidermis (arrowheads), although some melanophores are found subdermally, as
in D. rerio (arrow). (S) Higher magnification of bracketed region in
R, showing a melanin-containing extrusion body typical of teleost melanophore
death. Arrowhead indicates bounding membrane. n, neuromast. Melanin-containing
debris in P also is superficially located, as revealed by hexagonal outlines
of adjacent epidermal cells. (T) High magnification image of whole-mount
larva, showing extrusion body containing melanin granule (arrow) and staining
for dct mRNA (arrowhead). Scale bars: in A, 80 µm for A,C; in B,
40 µm for B,D; in E, 60 µm for E-H; in I, 80 µm for I-L; in P, 20
µm for P; in Q, 60 µm for Q,R; in S, 20 µm for S,T.
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