Biology Reference
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of metamorphosis giving rise to the many and varied adult pigment patterns
of other teleosts are largely unknown, though mutational and transgenic
resources for some (
Kelsh, 2004; Kelsh et al., 2004; Odenthal et al., 1996;
Parichy, 2006
), and evolutionary genetic strategies for others (
Miller
et al., 2007; Roberts, Ser, & Kocher, 2009
), offer significant potential for
future advances in this area.
4.4. Fin ray formation
Before and during metamorphosis, mesenchymal cells give rise to the fin en-
doskeleton, with rays growing from proximal to distal. Numerous pathways
regulate positioning and outgrowth of these rays and the joints within the
rays (
Mar
´
-Beffa & Murciano, 2010; Sims, Eble, & Iovine, 2009
). Early
proximo-distal patterning in the fin bud, largely controlled by Fgf signaling,
is thought to establish a “prepattern” for ray positioning. Sonic hedgehog
receptors are expressed in the proximal blastema, potentially inducing the
differentiation of bone-forming cells (
Laforest et al., 1998
). Many of these
morphogenetic processes are reactivated during fin regeneration (
Iovine,
2007
), and studying the normal metamorphic processes can lend insight
into regenerative processes. Interestingly, fin regeneration in zebrafish
is accompanied by enhanced expression of DIO3 and regenerative
progress is retarded when DIO3 activity is blocked pharmacologically
(
Bouzaffour, Rampon, Ramaug´, Courtin, & Vriz, 2010
), suggesting that
local T3 degradation promotes regeneration. By contrast, growth
cone formation of the regenerating lateral line is stimulated by TH
(
Bouzaffour et al., 2010
). Remaining unknown is the extent to which
hormonal mediators associated with normal metamorphosis are required
during regeneration of other tissues and how precisely these contribute to
particular cellular behaviors. The roles of these factors during normal fin
development remain largely unknown, but will be interesting to
uncover, particularly in light of the diversity of fin morphologies among
teleosts more generally.
In summary, larval metamorphosis in teleosts involves coordinated mor-
phological changes to many different organs; we now understand only a few
of the genetic requirements for these transitions. The mechanisms by which
these cascades are hormonally activated and coordinated remain largely un-
known. Particularly, considering the growing number of molecular re-
sources for nonmodel organisms (
Sarropoulou, Nousdili, Magoulas, &
Kotoulas, 2008; Volff, 2005
), the genetics of metamorphic events and
transitions in teleosts represents a promising field for future study.
