Mushroom body neuroblast clones homozygous for chinmo1 generated at newly hatched larval stage contains only one vertical and one horizontal axon bundle despite presence of many cell bodies. Mutant neuroblast clones also contain ectopic bundles of axons that exhibit a high affinity for the mAb Fas2, suggesting that most of the axons in chinmo1 mutant neuroblasts likely differentiate as α/β type of mushroom body projections.
There appear to be far more projections of the pioneer α/β type in chinmo1 mutant neuroblast clones, with qualitatively fewer γ type neurons.
Many chinmo1 mutant mushroom body single cell clones, despite being derived during early larval development, aberrantly acquire late-type neurite trajectories. For example, following induction of mitotic recombination at two days after larval hatching, γ-type neurons are obtained in only one-third of the single-cell mushroom body clones (as oppose to 100% in wild-type), while many more single-cell mushroom body clones that have both vertical and horizontal projections, and that appear to be either α'/β' or pioneer α/β neurons, are obtained. Furthermore, only α'/β and pioneer α/β neurons are detected among the single-cell clones that are induced at three days after larval hatching.
chinmo1 heterozygous larvae exhibit α'/β' neurons in chinmo1 single-cell/two-cell clones induced at as early as three days after larval hatching and exhibit a higher percentage of α'/β neurons (approximately 45%) at the 3.25 day after larval hatching induction than the wild-type control (approximately 36%) at the 3.5 day after larval hatching induction. This indicates that, as compared to wild-type, α'/β' neurons are generated at least 0.25 days earlier in the chinmo1/+ heterozygous animals. In addition, pioneer α/β neurons are also born precociously in a chinmo1/+ heterozygous background, as evidenced by the phenomenon that 47% (compared to 4% in wild-type) of the single-cell/two-cell clones, induced within 12-6hr before pupal formation, develop into pioneer α/β neurons in chinmo1/+ heterozygotes.
Approximately 80 pioneer α/β neurons are present in chinmo1/+ adult flies, compared to an average of 60 in wild-type.
Labeled chinmo1 single-cell/two-cell clones, induced in newly hatched larvae, innervate the D, instead of DL1, glomeruli. They also exhibit an axon arborization pattern resembling that of wild-type D-targeting projection neurons. Thus, chinmo1 mutant projection neurons, born in newly hatched larvae, apparently develop into the D-targeting projection neurons that also belong to the anterodorsal lineage, but are normally not generated until about two days after larval hatching. In contrast, chinmo1 is dispensable for specification of late-born cell fates, with both chinmo1 mutant, and wild-type clones, sharing the same morphological features of late-born projection neurons: all clones elaborated dendrites in both DM6 and VA1lm glomeruli.