FasII positive longitudinal axons and <i>sema</i>2b expressing commissural axons leave the CNS in <i>fra</i> mutant embryos expressing BcrAbl or Ablwt.

<p>Stage 16 embryos were stained with either mAb 1D4 against <i>FasII</i> [<b>A-D</b>] or anti-myc to visualize axons expressing the <i>sema</i>2b-<i>tau</i>-myc reporter [<b>E-H</b>]. Anterior is to the right. With 1D4, ISN (black arrow in A) and SN (white arrow in A) motor nerve roots are observed exiting the CNS in both [<b>A</b>] <i>fra³,</i> 1407-Gal4 heterozygote and [<b>B</b>] <i>fra³, 1407-G4/fra⁴</i> homozygote embryos. Using the 1407-Gal4 (1407-G4) driver, expression of either [<b>C</b>] BcrAbl or [<b>D</b>] Ablwt in a <i>fra³/fra⁴</i> homozygote causes additional FasII expressing axons (arrows) to leave the CNS, including axons normally within the medial most pCC/MP2 pathway (arrow in C). [<b>E-H</b>] A <i>sema2b</i>-Tau-myc reporter was used to assess a subset of commissural axons. [<b>E</b>] In a <i>fra³</i> heterozygote, <i>sema</i>2b expressing neurons extend axons into the anterior commissure (white arrowhead) and then turn anteriorly to form part of the longitudinal connectives (black arrowhead). [<b>F</b>] In homozygous <i>fra³/fra⁴</i> mutants most axon projections into the anterior commissure are still intact; however, extensions in the longitudinal connectives may be disrupted (arrowhead). In <i>fra³/fra⁴</i> embryos expressing either [<b>G</b>] BcrAbl or [<b>H</b>] Ablwt the axons of <i>sema</i>2b expressing neurons are observed projecting towards the periphery (arrows).