dorsal ventral patterning

bending

actomyosin-driven apical construction, wedge-shaped cells, hinge points

• result: neural groove and elevated folds

convergence

convergent extension, cell rearrangement, and growth of adjacent tissues

• result: opposing folds approach the dorsal midline

recognition and adhesion

filopodia / lamellipodia, cadherins, NCAM, eph/ephrins

• result: correct tissue contact one another

sealing and separation

nectins / afadin, JAMs, tight junctions, desmosomes

• result: closed tube and continuous surface ectoderm

notochord → floor plate

sonic hedgehog

• outcomes: floor plate, p3, pMN, other ventral domains

• higher / longer SHH exposure specifies more ventral identity

roof plate + dorsal ectoderm

BMPs & Wnts

• outcomes: dorsal progenitors and sensory-associated interneurons

• dorsal signals oppose and complement SHH

progenitor network

Gli proteins and cross-repressive transcription factors

• outcomes: sharp borders between initially graded responses

• combinations of factors encode position

mechanistic class: left-right signaling

consequence: failure to establish or transmit sided molecular identity

mechanistic class: outer dynein arm / docking

consequence: absent, abnormal, or poorly docked motility machinery

mechanistic class: dynein assembly factors

consequence: loss of outer and / or inner dynein arms

mechanistic class: axonemal organization

consequence: inner-arm loss and microtubule disorganization

notochord

midline axial mesoderm that supports the embryo and secretes SHH to organize ventral neural identity

somites

paired blocks of paraxial mesoderm that form vertebral, skeletal-muscle, and dermal derivatives

floor plate / roof plate

ventral and dorsal midline organizing centers of neural tube

morphogen

signal that elicits different cell responses according to exposure level and duration

situs inversus

mirror-image arrangement of many or all visceral organs

heterotaxy

discordant or ambiguous positioning and identity of visceral organs

holoprosencephaly

incomplete separation of the embryonic forebrain, often involving midline facial abnormalities