The goal of this study was to identify critical regions of a novel gene, Nance-Horan syndrome-like 1b (nhsl1b). It was previously discovered that C-terminal truncation of the Nhsl1b protein in nhsl1b mutants resulted in a loss of migration in the facial motor neurons of the hindbrain (Walsh et al. 2011). As nhsl1b expresses many isoforms, multiple targets were investigated in order to determine which transcript bears the largest impact on the motor neurons. Using confocal microscopy to observe immunostained embryos, we examined a mutation in an nhsl1b transcript that encodes a WHD, a domain that is known to function within the actin nucleation and polymerization pathways. In situ hybridization and injection of antisense morpholino oligonucleotides indicate that it is not the WHD but another transcript (ex1bnhsl1b) that is necessary for migration. The control experiments for rescuing the mutant phenotype have successfully been performed, but inducing expression of full length nhsl1b in the nhsl1b mutants is proving difficult.

Planar cell polarity (PCP) is a developmental signaling mechanism that establishes a polarity within the plane of an epithelium. PCP has been shown to play a role in guiding numerous neurodevelopmental processes such as convergent extension, neuron migration, and axon pathfinding. Certain commissural neurons in the dorsal spinal cord make a series of guidance decisions en route to the brain: first, a ventral projection along the D-V axis, followed by a midline crossing, and after exiting the floorplate, a dorso-anterior turn along the A-P axis. Here, we provide in vivo evidence that the axons of the Commissural Primary Ascending (CoPAs) neurons in zebrafish require the PCP genes fzd3a, vangl2, and scribble for rostral pathfinding both before and after crossing the midline. Dorsoventral guidance of CoPA axons is unaltered in fzd3a, vangl2, and scribble mutants, suggesting that the PCP signaling pathway only controls A-P guidance of CoPAs. Our results have provided evidence for two potential non- mutually exclusive models: (i) A-P axon guidance is achieved by cell-autonomous Wnt-Frizzled signaling or that (ii) A-P axon guidance is achieved by non-cell-autonomous PCP signaling in the neuroepithelial environment. The single-cell nature of the CoPA axon system allows for simple genetic manipulation and visualization, which will potentially elucidate the validity of either model. Scribble (Scrib), a member of the LAP family, plays a critical role in establishing and regulating cell polarization in epithelia and during cell migration. In zebrafish, Scrib mutants have defects in convergent extension (CE) cell movements and facial branchiomotor neuron (FBMN) migration. Despite our understanding of Scrib’s genetic role in neurodevelopment, little is known about the subcellular localization of endogenous Scrib in vivo during CE and FBMN migration. We have generated a monoclonal antibody against the C-terminus of zebrafish Scrib and have shown that this antibody is specific against endogenous Scrib in both western blot and immunocytochemical applications. Confocal microscopy of Scrib immunocytochemistry shows that at various developmental stages, Scrib distinctly localizes to basolateral membranes of non polarized epithelium, to the membrane in mesodermal cells undergoing CE, and to the membrane of migrating FBMNs. Furthermore, the distribution of Scrib puncta along membranes of FBMN- FBMN contact is significantly altered in the PCP mutant pk1b. Further application of our newly generated Scrib antibody will potentially lead to new insight on Scrib’s role in neurodevelopment.

Our work on RGMb demonstrates a clear and new role in the developing chick visual system. RGMb is expressed in distinct areas of the developing visual system: retinal ganglion cells (RGCs) of the retina, which are the only cells in the visual system that extend axons to the brain, as well as newly differentiated neuronal cells within the optic tectum (OT), the primary target of RGC axons. Knockdown of RGMb in RGCs at embryonic day 2 (E2) resulted in aberrant axon projection at E17, indicating that RGMb is required for axon development. Furthermore, knockdown of RGMb in the optic tectum at E5 resulted in disrupted cellular migration at E9, demonstrating that RGMb is involved in correct cell migration. Lastly, we demonstrated that RGMb binds to the Fibronectin III (3,4) domain of Neogenin, which provides a basis for determining the mechanism through which RGMb exerts its biological effects.

Our work on RGMb demonstrates a clear and new role in the developing chick visual system. RGMb is expressed in distinct areas of the developing visual system: retinal ganglion cells (RGCs) of the retina, which are the only cells in the visual system that extend axons to the brain, as well as newly differentiated neuronal cells within the optic tectum (OT), the primary target of RGC axons. Knockdown of RGMb in RGCs at embryonic day 2 (E2) resulted in aberrant axon projection at E17, indicating that RGMb is required for axon development. Furthermore, knockdown of RGMb in the optic tectum at E5 resulted in disrupted cellular migration at E9, demonstrating that RGMb is involved in correct cell migration. Lastly, we demonstrated that RGMb binds to the Fibronectin III (3,4) domain of Neogenin, which provides a basis for determining the mechanism through which RGMb exerts its biological effects.

Abstract Artificial Life is an interdisciplinary scientific and engineering enterprise investigating the fundamental properties of living systems through the simulation and synthesis of life-like processes in artificial media. One of the avenues of investigation is autonomous robots and agents. Mimicking of the growth and adaptation of a biological neural circuit in an artificial medium is a challenging task owing to our limited knowledge of the complex process taking place in a living organism. By combining several developmental mechanisms, including the chemical, mechanical, genetic, and electrical, researchers have succeeded in developing networks with interesting topology, morphology, and function within Artificial Computational Chemistry. However, most of these approaches still fail to create neural circuits able to solve real problems in perception and robot control. In this thesis a phenomenological developmental model called a Stochastic Evolutionary Neuron Migration Process (SENMP) is proposed. Employing a spatial encoding scheme with lateral interaction of neurons for artificial neural networks, which represent candidate solutions within a neural network ensemble, neurons of the ensemble form problem-specific spatial patterns with the desired dynamics as they migrate under the selective pressure. The approach is applied to gain new insights into development, adaptation and plasticity in neural networks and to evolve purposeful behaviors for mobile robots. In addition, the approach is used to study the relationship of spatial patterns, composed of interacting entities, and their dynamics. The feasibility and advantages of the approach are demonstrated by evolving neural controllers for solving a non-Markovian double pole balancing problem and by evolving controllers that exhibit navigation behavior for simulated and real mobile robots in complex environments. Preliminary results regarding the behavior of the adapting neural network ensemble are also shown and, particularly, a phenomenon exhibiting Hebbian-like dynamics. This thesis is a step toward a long range goal that aims to create an intelligent robot that is capable of learning complex skills and adapts rapidly to environmental changes.