Ca. Keller et al., MISEXPRESSION OF NAUTILUS INDUCES MYOGENESIS IN CARDIOBLASTS AND ALTERS THE PATTERN OF SOMATIC MUSCLE-FIBERS, Developmental biology, 181(2), 1997, pp. 197-212
nautilus (nau), one member of the myogenic regulatory family of bHLH-e
ncoding genes, is expressed in a subset of muscle precursors and diffe
rentiated fibers in the Drosophila embryo. To elucidate the role of na
utilus in myogenesis, we have misexpressed it using the GAL4-targeted
system. We find that ectopic expression results in lethality throughou
t Drosophila development. We analyzed the effects of embryonic express
ion in mesodermal tissues that include the cardioblasts of the dorsal
vessel as well most, if not all, of the presumptive somatic muscle pre
cursors. Immunohistochemical staining for muscle MHC revealed abnormal
ities that include an absence of cardial cells, coincident with the ap
pearance of novel muscle fibers adjacent to the dorsal vessel. Moreove
r, many cardioblasts express increased levels of muscle-specific genes
such as myosin, actin 57B, and Mlp60A, a protein that is restricted t
o the somatic, visceral, and pharyngeal muscles. These data suggest th
at the missing cardial cells have been transformed into cells with pro
perties similar to those of the somatic muscles. In addition, ubiquito
us expression of nautilus in somatic muscle cells of these embryos res
ulted in muscle pattern defects. Specifically, muscles that do not nor
mally express nautilus were frequently absent, and novel fibers were o
bserved in positions reminiscent of nau-expressing muscles. These data
imply that nautilus can alter the developmental program of muscle pre
cursors. In summary, we suggest that nautilus induces myogenic differe
ntiation in vivo when ectopically expressed in developing cardioblasts
and may affect the myogenic differentiation program of specific muscl
e fibers. (C) 1997 Academic Press.