BM108 - Block B

Two types of eukaryotic organism

Protists, metazoans

Protist overview

Simplest single-celled eukaryotes, still carry out life functions and show division of labour among the various cell structure

Metazoans overview

Multicellular animals that have cells specialised for particular functions

Bilateral symmetry

Better for moving in a direction, associated with cephalisation.

3 germ layers

Endoderm, Mesoderm, Ectoderm

Endoderm

Internal layer; lung (alveolar) cells, thyroid cells, digestive (pancreatic) cells

Mesoderm

Middle layer; cardiac muscle cells, skeletal muscle cells, tubule kidney cells, RBCs, smooth muscle cells (in gut)

Ectoderm

External layer; skin cells of epidermis, neuron on brain, pigment cells

Importance of body cavity

Isolation of organs for physiological independence, flexibility when moving, separate organs cushioned against damage, prevents organs from sticking to each other

Coelomate body plan

have a body cavity entirely within the mesoderm (called the coelom)

Cleavage

Division of cells in the early embryo. Undergoes rapid cell division with no significant growth. Produces a cluster of cells the same size as the zygote

Blastocyst

128 cells, contains an inner cell mass (ICM) and an outer cell mass

Embryoblast

Also known as an inner cell mass it is contained within the blastocyst and goes on to form the embryo. Forms embryonic stem cells

Trophoblast

Also known as an outer cell mass it exists outside the blastocyst and goes on to form the placenta

Pluripotent stem cell

theoretically can give rise to every cell type in the animal body. Proliferate indefinitely. First recognised in teratocarcinomas

Implantation

Blastocyst outer layer hatches, this exposes trophoblast cells to uterine wall. The mother releases LH to prepare the endometrium. The trophoblast implants and is fully embedded after 10 days

Amniotic cavity formation

The ICM pulls away from the trophoblast forming a hollow cavity

two cell layers

Epiblast; dorsal, next to the amniotic cavity, and Hypoblast; ventral, facing the yolk sac

Gastrulation

Follows implantation, defines cell layers and body shape. The epiblast layer undergoes complex rearrangement to form germ cell layers

Gastrulation - endoderm

Cells migrate towards the primitive streak and move through the layer towards the hypoblast, the first cells through become the definitive endoderm

Gastrulation - mesoderm

The cells that follow the endoderm form this intermediate layer

Epithelial tissue

ectoderm and endoderm - forms sheets of tissue

Mesenchymal tissue

Mesoderm - star shaped cells and do not attach to one another, they migrate freely

Neurulation

How the brain and spine form, notochord induces a fold in the overlying epiblast/ectoderm. Pinches off to form a neural tube

Neural plate formation

Notochord signals overlying ectoderm to become the neural plate

notochord regions

Somites, intermediate mesoderm, lateral plates

Somites

40 pairs of body segments (repeating units)

Intermediate mesoderm

Lateral to somites

Lateral plate

Splits to form coelom “body cavity”

Folic acid

Important for closure of neural tube occurring between week 3-4

Neural crest cells

Form sensory nerve cells and other structures

Spina bifida

Condition caused by incomplete neural tube closure, prevented by taking folic acid supplements during pregnancy

End of week 4

Embryo undercutting is complete. Somites have subdivided into sclerotome, myotome, and dermatome which form the vertebrae, skeletal muscles, and dermis respectively

Morphogen

Secreted molecule that induces cell fate decisions in recipient cells in a concentration gradient-dependent long-range manner.

French flag model

During early development, morphogen gradients generate different cell types in distinct spatial order

Zone of polarising activity

Secretes a morphogen that sets up the thumb-to-little finger organisation of the hand

Situs inversus

Body organs are swapped over

First trimester

Early cell divisions, establishment of germ layers (“germinate”), beginning of organogenesis

Second trimester

Organogenesis completes

Third trimester

Fetal growth, organ systems functional

Homogametic

Females; Gametes (eggs) are the same, always contain the X chromosome

Heterogametic

Males; gametes (sperm) either X or Y

SRY

Gene on the Y chromosome that controls male characteristics. Codes for a transcription factor that promotes male development and suppresses female development

Anti-Mullerian Hormone (AMH)

Gene on chromosome 19 that codes for the female gonad repressor

SRY process

SRY → SOX9 → FGF9 (growth factor) → testes → AMH

Turner’s syndrome

XO chromsome; female, do not mature sexually. Short stature, other congenital abnormalities (e.g. webbed neck)

Klinefelter’s syndrome

XXY; male, sterile, small testes, may have breast growth. Tend to be tall, may have mild mental impairement

metazoans

animals; multicellular eukaryotic organisms

cephelisation

Evolutionary trend where sense organs, mouth, and nervous tissue concentrate at the front to form a head

ENU mutagenesis

Genetic technique that uses N-ethyl-N-nitrosoura to induce random point mutations in animal germ cells

Lissencephaly

Failed neural migration leads to “smooth brain” condition where folds fail to form. Can be due to virus, lack of oxygen, or mutation

Tubulin

Globular protein family whose α β structures form microtubules

Microtubules

major component of the eukaryotic cytoskeleton, provide shape/structure to cell

Neural groove

Shallow groove on neural plate that later becomes the neural tube

Neural crest

Formed between ectoderm and neural plate during neurulation from the neural folds

Somites

Bilaterally paired blocks of mesoderm formed in segmented animals. Subdivide into cells that give rise to specific body parts

Wnt8

Injection of mRNA into dorsal marginal zone induce a complete secondary axis (e.g. two heads)

Nodal

Injection of mRNA into dorsal marginal zone can induce a secondary partial axis

Shh - Sonic hedgehog protein

Major signalling molecule controls organisation of CNS and organogenesis, uses french flag model

Patched

Primary receptor and inhibitor of Shh

Patched for Shh

Morphogen receptor, signals to nucleus to initiate appropriate differentiation programs within the cell

HOX genes

Dictates head-tail body plan. Studied in Drosophila fruit flies (8 HOX genes). Humans have 39

Aneuploidy

Genetic disorder resulting from non-disjunction in meiosis where total chromosomes doesnt equal 46. Trisomy is one extra, monosomy is one missing.

Anatomy of a neuron

Cell body → dendrite → axon → synapse → spine

Spemann-Mangold organiser

Group of cells that induce neural tissues during development in amphibian

BMP

Vital growth factors belonging to TGF-B family that stimulate growth of new bone and tissue. Essential for controlling cell differentiation and apoptosis

BMP inhibitors

Chordin, noggin, follastatin

Chordin, noggin, and follastatin

Blocks BMP signalling from forming epidermis, allows ectoderm cells to adopt their default pathway and become neural cells

Three types of patterning

Dorsoventral, Rostrocaudal, forebrain

Rostrocaudal patterning

Organises along head-tail axis

Dorsoventral patterning

Organises front-back axis

Nervous system regions - rostrocaudal patterning

Forebrain, midbrain, hindbrain, spinal cord

Ventral neural tube patterning

Patterned by Shh protein secreted from notochord

Dorsal neural tube patterning

Patterned by BMPs

Pax6 and Emx2

Transcription factors that form oppposing gradients in the developing embryonic brain. Mutually repress each other’s expression

FGF8

Establish the rostrocaudal pattern of the cerebral cortex

Progenitor cells (overview)

Can divide into a specific type of mature cell. Similar to stem cells, but more specialised and can only divide a limited number of times

Progenitor cells (potential)

Unipotent, sometimes oligopotent. Can divide (assymetrically) into one neuron and one glia, one neuron and one P cell, or (symmetrically) two P cells

Neural stem cells

Self-renewing multipotent cells that become neurons, astrocytes, and oligodendrocytes

Radial glial cells

Bipolar progenitor cells responsible for producing neurons in the cerebral cortex

Astrocytes

Star shaped glial cells in the brain and spinal cord.

Ganglionic eminence (GE)

Inhibitory neurons migrate into the cortex

Neurotrophins

NGF (Nerve growth factor), BDNF, NT-3

NGF Receptors

TrkA = Tropomyosin receptor kinase A

BDNF, NT-3 receptors

TrkB, C, p75

Cortical laminar formation

Inside first - outside last (cells in first become the inside layer)

Cortical GABAergic neurons

Tangenital migration - a developmental brain process where immature neurons travel parallel to the brain’s surface and perpindicular to radial glial cells

Synapse formation

Neuronal polarity, axon guidance, synaptogenesis, refining/plasticity

Alzheimers - Amyloid cascade hypothesis

deposition of amyloid β protein (ABP) causes alzheimers pathology and that the symptoms are because of this

Neurological diseases (loss of neurons)

Alzheimers, parkinsons, stroke

Neuropsychiatric diseases (overview)

Change in neural circuits

Neuropsychiatric disease (examples)

Schizophrenia, depression, addiction, ASD

Adventitial cells

constitute a significant part of the vessel wall structure, reactive oxygen species

Vein/artery structure (inside-out)

Endothelium, tunica intima, tunica media, tunica externa

Arteriole structure (inside-out)

Endothelium, basement membrane, smooth muscle cells