Neural Development: Growth and Guidance of Axons (Slides)

Vocabulary flashcards covering key concepts from growth cone structure, neurite development, dendritic patterning, and axon guidance cues (netrin, DCC, Slit/Robo, floor/roof plate), as discussed in the slides.

Growth cone

The motile tip of a growing axon that senses environmental cues and steers axon extension via cytoskeletal rearrangements.

Lamellipodium

A sheet-like, actin-rich network at the leading edge of the growth cone that drives forward extension.

Filopodium

Slender, finger-like projections from the growth cone that probe the environment and guide navigation.

Neurite

Any projection from a neuron, including dendrites and the axon; early neurites compete to become the axon.

Axon vs. dendrite commitment

During development, one neurite becomes the axon while others become dendrites; cytoskeletal reorganization and genetic cues bias this choice.

Dendritic self-avoidance

Dendritic branches from the same neuron repel each other to avoid self-overlap, enabling even spacing; mediated by protocadherins.

Dendritic tiling

Dendrites from different neurons cover their own territories with minimal overlap to maximize coverage; also mediated by protocadherins.

Protocadherins (DSCAM)

Cell-surface proteins providing self/non-self identity for neurons; bind homophilically to produce repulsion and regulate dendritic patterning.

PAR proteins

Polarity regulators that organize the cytoskeleton to orient axon and dendrite outgrowth during development.

Cytoskeleton

Network of actin filaments and microtubules that shapes neurite outgrowth and branching; dynamics underlie axon guidance.

Growth cone receptors

Surface receptors at the leading edge that detect environmental cues (attractants or repellents) to steer growth.

Second messengers

Intracellular signals such as calcium and cyclic AMP that relay external cues to cytoskeletal changes in the growth cone.

Netrin

Secreted cue that guides axons; binds the DCC receptor to attract toward the midline; later modulation via Robo regulates crossing.

DCC (Deleted in Colorectal Cancer)

Receptor for netrin; mediates attractive signaling guiding axons toward sources of netrin.

Slit and Robo

Slit is a secreted repellent; Robo is its receptor; together they drive midline repulsion after crossing and help steer axons.

Floor plate

Midline structure in the developing spinal cord that secretes cues guiding commissural axons across the midline.

Roof plate

Dorsal midline structure that initially provides repulsive cues to guide axons away from the midline before crossing.

Optic chiasm

Midline point where retinal ganglion cell axons decide to cross to the contralateral side or remain ipsilateral; guidance involves multiple cues.

FB/FA gradients

Lecture-noted guidance gradients that regulate retinal mapping; FB and FA gradients interact with retinal and tectal cues to direct axon targeting.

Cadherins

Calcium-dependent adhesion molecules that promote homophilic cell–cell adhesion and influence cytoskeletal organization during guidance.

Laminins and Integrins

Laminins are extracellular matrix proteins that bind integrin receptors on neurons to promote adhesion and directed growth.

Immunoglobulin receptors

Neuronal surface receptors with Ig-like domains that signal to influence cytoskeletal dynamics and axon guidance.

Fasciculation

Growth cone uses an existing axon as a scaffold to extend along it, aiding pathfinding via axon-axon adhesion.

Retinal mapping frog experiment

Experiments rotating the frog eye showed axons project to original targets despite inverted retinal layout, indicating intrinsic guidance cues.

Spinal cord midline crossing mechanisms

Netrin attracts commissural axons to the floor plate; after crossing, Robo-Slit signaling repels to prevent recrossing and guide rostral progression.

Conservation across species

Many axon guidance mechanisms are evolutionarily conserved across organisms (e.g., C. elegans, Drosophila, vertebrates).