N-Terminal and Central Domains of APC Function to Regulate Branch Number, Length and Angle in Developing Optic Axonal Arbors in Vivo

During formation of neuronal circuits, axons navigate long distances to reach their target locations in the brain. When axons arrive at their target tissues, in many cases, they extend collateral branches and/or terminal arbors that serve to increase the number of synaptic connections they make with target neurons. Here, we investigated how Adenomatous Polyposis Coli (APC) regulates terminal arborization of optic axons in living Xenopus laevis tadpoles. The N-terminal and central domains of APC that regulate the microtubule cytoskeleton and stability of β-catenin in the Wnt pathway, were co-expressed with GFP in individual optic axons, and their terminal arbors were then imaged in tectal midbrains of intact tadpoles. Our data show that the APCNTERM and APCβ-cat domains both decreased the mean number, and increased the mean length, of branches in optic axonal arbors relative to control arbors in vivo. Additional analysis demonstrated that expression of the APCNTERM domain increased the average bifurcation angle of branching in optic axonal arbors. However, the APCβ-cat domain did not significantly affect the mean branch angle of arbors in tecta of living tadpoles. These data suggest that APC N-terminal and central domains both modulate number and mean length of branches optic axonal arbors in a compensatory manner, but also define a specific function for the N-terminal domain of APC in regulating branch angle in optic axonal arbors in vivo. Our findings establish novel mechanisms for the multifunctional protein APC in shaping terminal arbors in the visual circuit of the developing vertebrate brain

Visual Arts Enhance Instruction in Observation and Analysis of Microscopic Forms in Developmental and Cell Biology

Two important skills for scientists in developmental and cell biology, as well as in fields such as neurobiology, histology and pathology, are: 1) observation of features and details in microscopic images of cells, and 2) quantification of cellular features observed in microscopic images. However, current training in developmental and cell biology does not emphasize observation and quantitative analysis of microscopic images, and it is unclear how best to teach students these skills. Here, we describe our experiences applying visual artistic approaches to instruct undergraduate and graduate students in how to observe and analyze cellular forms in microscopic images. At Loyola Marymount University, we used representational drawing to enhance undergraduate students’ skills in observation of fine cellular details in microscopic images of embryos. At Touro University California, we paired abstract paintings with microscopic images of tissues to engage masters and medical students in learning quantitative measurements of cellular features. Overall, this paper explains specific ways in which visual arts can be used to instruct and engage students in observation and analysis of microscopic images of cells and tissues

Morphometrics in Developmental Neurobiology: Quantitative Analysis of Growth Cone Motility in Vivo

In order for the nervous system to function properly, neurons in the brain must establish specific connections during embryonic development. Formation of neuronal circuits involves axons extending from cell bodies and navigating through diverse tissues to reach their targets in the brain. Once axons reach their target tissues, they arborize and make synaptic connections. Axon pathfinding is driven by dynamic motility behaviors expressed by terminal growth cones at the tips of the axons. Here, we applied morphometrics to determine quantitative values for six morphological and motility parameters for growth cones of optic axons navigating through the optic tract of a living brain preparation from a Xenopus laevis tadpole. Our results demonstrate an increase in length, decrease in width, increase in perimeter, decrease in area, increase in number of filopodia, and a decrease in number of lamellipodia, of the growth cones in the optic tract. Therefore, optic axonal growth cones become less circular and more elongated and protrusive during their navigation through the optic tract. Quantitatively deconstructing parameters of growth cone motility is necessary to determine molecular, cellular, and biophysical mechanisms of axon pathfinding, and to formulate computational analyses of developing neuronal connectivity in the brain

Visualizing Morphogenesis with the Processing Programming Language

We used Processing, a visual artists’ programming language developed at MIT Media Lab, to simulate cellular mechanisms of morphogenesis – the generation of form and shape in embryonic tissues.  Based on observations of in vivo time-lapse image sequences, we created animations of neural cell motility responsible for elongating the spinal cord, and of optic axon branching dynamics that establish primary visual connectivity.  These visual models underscore the significance of the computational decomposition of cellular dynamics underlying morphogenesi