BIOMG 1350 Prelim 3 (lectures)

How do cells go from a single cell to an organism?

It would start with cell proliferation, then cell specialization, then cell interaction, and lastly cell movement

Cell proliferation

the production of one cell from many

Cell specialization

cells start to have unique characteristics

Cell interaction

cell behavior coordination between cell neighbors

cell movement

cell rearrangement to create structured tissues and organs

What do conserved mechanisms establish?

Basic animal body plan

Fertilization

the beginning of a new organism

What occurs during fertilization?

Two haploid genomes are united to create a diploid zygote.

- fertilization only occurs between members of the same species

- one sperm to one egg

What does fertilization initiate?

embryonic development

What controls embryonic development at the very early phase?

maternal components, or egg materials from the mother

After the maternal components, what drives embryonic development?

the embryo will make its own gene products/zygotic components

Oocyte

egg

Characteristics of an oocyte

- haploid nucleus

- maternal components

What are maternal components?

nutrients, biosynthetic machinery, mitochondria, genetic information (i.e. mRNAs and proteins) needed for early embryonic development

Sperm

haploid nucleus, contains centrosome, activates development

Cleavage

cell division WITHOUT cell growth

What does the cleavage stage lack?

g1 and g2 phases

What is cleavage division reliant on?

maternal components

What are blastomeres?

Cells created by cleavage

What is a blastula?

the embryo at the end of cleavage

Gastrulation

The reorganization of the embryo into three germ layers called the endoderm, mesoderm, and ectoderm

When is gastrulation in embryogenesis?

The first morphogenetic event that reforms the embryo into three germ layers: endoderm, mesoderm, and ectoderm.

Morphogenesis

the creation of organized forms

- formation based on different cell behaviors

What are the three major axes?

anterior posterior (head and tail), dorsal ventral (back and belly), left right (lateral)

What event in embryogenesis is exclusive to vertebrates?

Neurulation

What are the four stages of neurulation?

shaping, folding, elevation, convergence, closure

Neurulation

central nervous system creation, MAJOR MORPHOGENETIC EVENT

Organogenesis

organ formation

What is created during organogenesis?

1.internal organs (e.g., heart, kidney, lung, liver, etc)

2. limbs (fins, arms, legs)

3. sensory organs (eyes, ears)

What are the central questions in developmental biology?

How are cells different? How do cells organize into tissues or organs? How do tissues and organs develop in the right location and orientation? How do organisms maintain their tissues and organs?

How do we study development?

Descriptive embryology, experimental embryology, developmental genetics, comparative embryology

Descriptive embryology

Observing the cell as it grows and fate mapping (lineage tracing)

What is fate mapping?

labeling or adding a dye (e.g. GFP) to one cell or a group of cells during at the start of development and then observing what the cell becomes later

(add a dye at the start and watch what happens to the cell[s])

Experimental embryology

experimental manipulation to the embryo by removing, rearranging, transplanting, or isolated growth of a part of the embryo in isolation

What is cutting in experimental embryology?

cells are separated

What is experimental embryology possible in?

Embryos that are big relatively, easily manipulated, and can develop outside of the mother (e.g., sea urchin, chick, and frog)

Developmental Genetics

Studying mutants

How is developmental genetics studied?

comparing normal function of a gene with a mutated version

- gene is mutated and change is observed

What are developmental genetics possible in?

Organisms that are amendable to genetic analysis

Comparative embryology

comparing the physiology. evolutionary developmental biology

Differentiated cell

- specialized cells (e.g., skin, muscle, etc.)

- refers to the final or intermediate stages

Cell/developmental fate

developmental outcome of a cell/group of cells

Is it possible for cells to be committed to a fate without looking differentiated

Yes

What are the two processes to cell fate commitment?

specification and determination

What is specification?

A cell fate is committed but reversible

What is determination?

irreversible and committed

When is a cell neither specified nor determined?

when isolated in a neutral environment, a different fate is expressed than it would normally be

When is a cell specified but not determined? Assuming isolated in a neutral environment

the cells express its normal fate

When is a cell determined?

when a cell, regardless of environment (i.e. neutral or new), still expresses its normal fate

When is a cell NOT determined but SPECIFIED

the cell would express its original fate in a neutral environment, but with environmental influences/new environment, the cell changes

(i.e. muscle changes to neuron when surrounded by neuron cells)

How do we experimentally identify a cell as determined?

when transplanted, the cell keeps the original fate

Describe fate commitment progression

each step is irreversible, cells have memory, and becomes increasingly restrictive as development continues

What did the sea urchin isolation experiment show?

each sea urchin blastomere can create a normal larva

What was Hans Spemann fantastical experiment?

egg is enucleated by transplanting a somatic cell nucleus into it, leading to the creation of a frog

Do differentiated cells contain information to create the entire organism or only information to perform its function?

Differentiated cells contain all the genetic information to produce an entire organism

- contains all the information

who conducted the first animal cloning experiment?

John Gurdon (1962)

What happened during the first animal cloning experiment?

nucleus from fully differentiated tadpole skin cell resulted in normal frog development

What did Ian Wilmut do?

Successfully cloned a sheep from adult mammary cell

Why are cells different?

cells are different because they express different genes

Differential gene expression theory

1. genome is constant in all somatic cells (all somatic cells have the same genome)

2. only a small portion of the genome is expressed in any cell type

3. Unused genes aren't mutated or destroyed; they can still be expressed

cell intrinsic mechanisms

autonomous cell mechanisms

cell extrinsic mechanisms

reliant/non-autonomous cell mechanisms

What is an example of cell intrinsic mechanisms

asymmetric cell division

What is Asymmetric cell division?

different sets of molecules in the two daughter cells

When does asymmetric cell division occur?

Before division, Cytoplasmic determinants are localized asymmetrically, so when it divides, it leads to two different cells

Cytoplasmic determinants

cytoplasmic molecules that influence cell fates

How do cells from symmetric cell division become adopt different fates?

Environmental influences that act on the cells after birth

what is inductive signaling?

nearby cells influence other cells

how do cell signals function?

all or nothing mechanism or concentration dependent manner (morphogens)

What are morphogens?

Diffusible, secreted molecules from a signaling cell(s)

What do morphogens form?

a graded distribution

Describe the morphogen concentration gradient

morphogen concentration is higher at the source and decreases as it gets farther from the source

How does the varying local concentration of morphogen affect the cellular response?

Different concentrations change the cellular response

What kind of pattern does a morphogen establish?

morphogens provide a mechanism to create a reproducible pattern to specify fates

Sonic hedgehog (Shh)

mRNA that is responsible for digits

What does inappropriate Shh expression lead to?

extra digit formation

What is lateral inhibition

Two cells are born the same and produce the same amount of molecule X and inhibit the production of molecule X in the other molecule

how does lateral inhibition lead to different cells?

at some point during lateral inhibition, one cell will inhibit another cell more, leading to one cell producing more of molecule X and the other less molecule X. This leads to two different cells because of the different molecule X concentrations

When does lateral inhibition work?

Between two neighboring cells that are directly next to each other

How many cell-cell signaling pathways regulate cell-cell signaling in animal development?

A small number of conserved cell-cell signaling pathways

What mediates cell-cell signaling in animal development?

Transforming growth factor beta, wnt, hedgehog, notch, receptor tyrosine kinase and more

Are all inductive signaling responses the same or different?

the same signal can have a different effect depending on the combination; the same inductive signal can lead to different responses

What is sequential induction

cell B sends an inductive signal to A, leading to cell C. cell C then sends a signal to surrounding A and B cells, leading to more new cells

basically, inductive signaling leads to a new cell type, and the new cell affects surrounding cells

What are examples of cell extrinsic mechanisms

lateral inhibition, inductive signaling/morphogen gradients

What are the ending results of cell autonomous and cell nonautonomous mechanisms

different gene expression, leading to different fates

About how many genes, out of 21000 protein coding genes in humans, are devoted to cell signaling?

more than 7000 protein-coding genes are devoted to cell signaling

What are the general principles of signaling?

a ligand bonds with the receptor, which triggers an intracellular signaling pathway. This triggers an effector, which can have a multitude of effects.

What is a ligand

signaling molecule that can be in the form of a

1. protein

2. peptide

3. amino acid

4. nucleotides

5. steroids

6. fatty acid derivatives

7. gases

What does the ligand do to a receptor?

it bonds with a receptor

What do intracellular signaling pathways do?

relay, amplify, integrate, or distribute

What do effectors do?

effectors may change gene expression, metabolism, cell shape or movement

What is signal transduction?

the process where an extracellular signal is converted into some response by intracellular effectors that alter cell behavior

Over what distance to signals act?

Long and short distances

What kind of signaling methods are there?

endocrine (through blood stream)

Paracrine

synaptic

contact dependent

What is endocrine signaling?

a hormone is released from a cell. It then travels through the blood stream and to the target cell

What is paracrine signaling?

A nearby cell releases the signal to nearby cells (ex: morphogen)

What is autocrine signaling?

a cell releases a signal to activate a signal transduction on itself

What is synpatic signaling

When activated, an electrical signal travels down the axon of a neuron. it then cuases the release of neurotransmitters at the nerve terminal

Describe how far an axon can be from the cell body.

The axon of a neuron can be far from the cell body

What are synapses

the gap between the target cell and the neuron