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Fig. 1. schizo is required for commissure formation. Frontal views of
dissected central nervous system (CNS) preparations of stage-16 embryos. (A-C)
Stained for the presence of all CNS axons using Mab BP102. (D-F) Stained for
the presence of the Myc epitope using Mab 9E10. (C) The midline glial cells
are labeled by ß-galactosidase expression using the AA142
enhancer. Anterior is up. (A) Wild-type embryos are characterized by a regular
arrangement of longitudinal connectives (lc) and segmental commissures (ac,
pc). (B) In homozygous schizoC1-28 mutant embryos the
formation of commissures is reduced (arrow). The longitudinal connectives are
thinner. (C) Homozygous schizoU112 embryos display a
stronger commissural phenotype. Most frequently the anterior commissure is
affected (arrow). In neuromeres with reduced commissures the midline glial
cells migrate toward the connectives (arrowhead). (D) In wild-type embryos the
sema-
myc marker is expressed in only a few neurons in each hemineuromer.
The corresponding axons cross the midline in one fascicle and turn anterior
within the longitudinal connective. (E,F) In mutant
schizoU112/C1-28 embryos the sema-
myc marker cannot
be detected in about 50% of the commissures. Within the longitudinal
connectives we noted a defasciculation of the Myc positive axon bundles
(arrow).