ECTODERM AF

Organogenesis

Formation of organs and tissues after gastrulation

Germ layers

Embryonic layers that give rise to all tissues and organs

Ectoderm

Germ layer that forms nervous system, epidermis, and neural crest derivatives

Mesoderm

Germ layer that forms muscles, connective tissue, blood, and notochord

Endoderm

Germ layer that forms internal epithelial linings of digestive and respiratory systems

Meristem

Plant stem cell region responsible for continuous growth

SAM (Shoot Apical Meristem)

Meristem at shoot tip responsible for shoot, leaf, and flower development

RAM (Root Apical Meristem)

Meristem at root tip responsible for root growth and development

Auxin

Plant hormone promoting differentiation and downward signaling from SAM to RAM

Cytokinin

Plant hormone promoting cell division and stem cell maintenance

Central Zone (CZ)

Stem cell reservoir region of the SAM

Peripheral Zone (PZ)

SAM region where cells begin differentiating into lateral organs

Organizing Center (OC)

Region maintaining stem cells in the SAM

Quiescent Center (QC)

Slowly dividing root stem cell maintenance region in RAM

Totipotency

Ability of a single cell to produce an entire organism

Dedifferentiation

Process where specialized cells revert to a less specialized state

Redifferentiation

Process where dedifferentiated cells become specialized again

Callus

Mass of undifferentiated plant cells formed during regeneration or tissue culture

In vitro culture

Growth of cells or tissues outside the organism in controlled conditions

Arabidopsis thaliana

Model organism commonly used in plant developmental biology

Blastula

Hollow ball of cells formed after cleavage

Blastocyst

Mammalian blastula containing trophoblast and inner cell mass

Trophoblast

Outer blastocyst layer involved in implantation and placenta formation

Inner Cell Mass (ICM)

Blastocyst cell cluster that forms the embryo proper

Blastocoel

Fluid-filled cavity inside blastula or blastocyst

Implantation

Attachment of blastocyst to the uterine endometrium

Bilaminar embryonic disc

Embryonic structure composed of epiblast and hypoblast

Epiblast

Embryonic layer that forms all three germ layers

Hypoblast

Embryonic layer contributing mainly to extraembryonic structures

Gastrulation

Process forming the three germ layers through cell migration

Trilaminar embryo

Embryo containing ectoderm, mesoderm, and endoderm

Primitive streak

Site of epiblast cell migration during gastrulation

Ingression

Migration of individual cells inward from an epithelial layer

Invagination

Folding inward of a sheet of cells

Archenteron

Primitive gut formed during gastrulation

Morphogenesis

Development of tissue and organ shape through coordinated cell movements

Placode

Thickened ectodermal region initiating organ development

Epithelial-mesenchymal interaction

Reciprocal signaling between epithelium and mesenchyme during organ formation

Mesenchyme

Loosely organized migratory embryonic connective tissue

Shh (Sonic Hedgehog)

Morphogen involved in neural tube, tooth, and ventral patterning development

BMP (Bone Morphogenetic Protein)

Morphogen involved in epidermal and dorsal neural patterning

Noggin

BMP inhibitor promoting neural tissue formation

Chordin

BMP inhibitor involved in neural induction

Follistatin

BMP inhibitor promoting neural development

Wnt

Signaling pathway regulating cell fate, migration, and patterning

Edar

Signaling molecule involved in hair and ectodermal appendage development

Neural induction

Process where ectoderm becomes neural tissue through BMP inhibition

Neurulation

Formation of the neural tube from ectoderm

Neural plate

Thickened dorsal ectoderm that forms the neural tube

Neural groove

Midline depression formed during neural plate folding

Neural folds

Elevated edges of the neural plate during neurulation

Neural tube

Closed ectodermal tube forming brain and spinal cord

Notochord

Mesodermal structure inducing neural development and ventral patterning

Primary neurulation

Neural tube formation through folding of the neural plate

Secondary neurulation

Neural tube formation through cavitation of a solid cord

Medullary cord

Solid precursor structure formed during secondary neurulation

Cavitation

Formation of a hollow cavity within a solid structure

Rostral

Toward the head or anterior region

Caudal

Toward the tail or posterior region

Dorsal

Toward the back side of the embryo

Ventral

Toward the belly side of the embryo

Convergence

Movement of tissues toward the embryonic midline

Fusion

Joining of neural folds during neural tube closure

Apical constriction

Narrowing of the apical side of cells causing bending and folding

Median Hinge Point (MHP)

Central neural plate bending region

Dorsolateral Hinge Point (DLHP)

Lateral neural plate bending regions

Roof plate

Dorsal neural tube signaling center producing BMP

Floor plate

Ventral neural tube signaling center producing Shh

Morphogen gradient

Concentration-dependent signaling pattern influencing cell fate

Sensory neurons

Dorsally patterned neurons receiving sensory input

Motor neurons

Ventrally patterned neurons sending motor output

Cadherins

Cell adhesion molecules important for tissue separation and organization

N-cadherin

Cadherin expressed mainly in neural tissue

E-cadherin

Cadherin expressed mainly in epithelial tissue

Extracellular Matrix (ECM)

Network of proteins outside cells supporting tissues and migration

Fibronectin

ECM protein involved in cell adhesion and migration

Laminin

ECM protein supporting basement membranes and cell attachment

Collagen

Structural ECM protein providing tissue support

Closure point

Site where neural tube fusion begins

Bidirectional zippering

Neural tube closure spreading in two directions from a closure point

Neuropore

Open ends of neural tube before complete closure

Anencephaly

Neural tube defect caused by anterior closure failure

Spina bifida

Neural tube defect caused by posterior closure failure

Folic acid

Vitamin important in prevention of neural tube defects

Neural crest cells (NCCs)

Migratory ectoderm-derived cells forming diverse tissues

Neural plate border

Boundary between neural plate and non-neural ectoderm where NCCs arise

Epithelial-to-mesenchymal transition (EMT)

Process where epithelial cells become migratory mesenchymal cells

FoxD3

Transcription factor required for neural crest specification

Slug

Transcription factor required for neural crest migration

Cranial neural crest

NCC population forming craniofacial structures

Cardiac neural crest

NCC population contributing to heart septation

Vagal neural crest

NCC population contributing to enteric nervous system

Trunk neural crest

NCC population forming peripheral ganglia and melanocytes

Sacral neural crest

NCC population contributing to enteric nervous system posteriorly

Melanocytes

Pigment-producing skin cells derived from NCCs

Adrenal medulla

Inner adrenal gland region derived from NCCs

Sympathetic ganglia

Autonomic nervous system ganglia derived from NCCs

Enteric ganglia

Neural networks controlling gut activity

Dermamyotome

Somite region contributing to dermis and skeletal muscle

Somites

Segmented mesodermal blocks along embryo axis