Title: Development of leg motor neurons in drosophila melanogaster
Description: Drosophila larval and adult stage forms are very different. Drosophila larvae move using undulatory body muscle contractions, while adult flies walk and fly using legs and wings. Leg motor neurons control multi-jointed leg movement by coordinately regulating leg muscle contractions. With the aim of understanding how Drosophila leg motor neurons are specified, in Chapter One, I give a general introduction of the mechanisms that regulate motor neuron generation and specification. In Chapter Two, I show that adult Drosophila leg motor neurons are mostly generated de novo during larval stages in a lineage dependent manner. Although leg motor neurons are born from 11 lineages, nearly two thirds of leg motor neurons are born from two major lineages: Lin A and Lin B. I describe the individual leg motor neuron birth orders, axonal and dendritic morphologies by using single cell labeling methods. Each motor neuron that has unique axonal targeting and dendritic architecture is born in a stereotypic birth order from a specific lineage.

Leg motor neurons targeting similar muscles share dendritic territory in the CNS and subsequently form a dendritic myotopic map in the CNS. These findings provide critical information about how individual leg motor neurons are generated, and how individual leg motor neuron axons and dendrites look like. In Chapter Three, I describe the results of a candidate gene approach. In vertebrate systems, Hox genes and Hox cofactors regulate spinal cord motor neuron identity. Although much work has been done addressing the function of Hox genes and Hox cofactors in vertebrate motor neuron development, the function of Hox genes and Hox cofactors in motor neuron dendritic arborization has not been clearly addressed. With this aim in mind, I describe the function of Hox genes and Hox cofactors in Drosophila leg motor neuron development by removing Hox genes and Hox cofactors in both entire lineages and individual motor neurons. I show that Hox genes and Hox cofactors are required for motor neuron survival, and proper axonal and dendritic targeting.

In Chapter Four, I discuss about how segmental and temporal identities of leg motor neurons are specified and how the axonal targeting of leg motor neurons at the early stage is achieved. Finally, in the Appendix, I show my attempts to find leg motor neuron specific molecular markers.