| dc.description | The goal of this thesis was to examine neural and muscular development in the well studied gastropod Ilyanassa obsoleta. A relatively sophisticated larval nervous system (LNS) was revealed using immunocytochemical techniques combined with confocal microscopy. The LNS first appeared in the trochophore stages and became more elaborate during veliger stages. Neurons containing monoamines and neuropeptides were observed in the apical organ, peripheral regions and developing ganglia destined to become the adult central nervous system. Furthermore, neural elements were also associated with ciliary bands and muscle fibers in the velum and near the mouth cavity suggesting roles in swimming and feeding. Exposure to exogenous monoamines, synthetic analogues and neuropeptides had significant effects on such behaviours. Distal-less was expressed in the ectoderm and then later in neural ectodermal regions from which the developing ganglia were formed. The expression pattern suggested a conserved role of the gene in ectoderm specification and development of migratory neurons. Distal-less was not expressed in other regions of the developing larval nervous system and therefore, separate mechanisms likely govern the differentiation of different parts of the larval nervous system. This hypothesis was further examined in experiment; in which the D macromere was ablated. The resultant larvae lacked distal-less in the ectoderm and neural ectoderm and only neurons outside the developing central ganglia were observed. Finally, using F-actin labeling, the development and anatomy of the larval musculature was examined. The larval musculature was relatively extensive. Two major muscle systems were identified, the larval retractor and pedal retractor muscles. These muscles differed in their anatomy, timing of appearance and fates during metamorphosis. Cell lineage tracing indicated that these major muscle groups had different cellular origins. Additionally, cell ablations and chemical block of early inductive signals, indicated that induction signals were also necessary to form organized muscle systems. | en_US |
