CBNS108 Lectures 3+4

Organize the following developmental events from earliest to latest: AP axis elongation and neurulation, morphogenesis in the gastrula, cleavage without growth, organogenesis in the pharyngula, formation of blastula/blastocyst.

Cleavage without growth—>formation of blastula/blastocyst—>morphogenesis in the gastrula—>AP axis elongation and neurulation—>organogenesis in the pharyngula

How does the cell have polarity before fertilization?

Through the animal-vegetal axis

Which hemisphere does fertilization occur in the cell? Why?

Animal; sperm receptors are concentrated in the animal hemisphere, animal side is less dense and easier for sperm to penetrate.

What are blastomeres?

Cells deriving from cleavage divisions

What is unique about patterns of cleavage divisions in the Xenopus?

They are fixed

Where is the grey crescent formed?

Opposite to sperm entry point

The first cleavage division typically divides the _________ equally into two cells

gray crescent

Initial cleavage divisions are ________(symmetrical/asymmetrical) and __________(synchronous/asynchronous).

Symmetrical; asynchronous

Stage where there are 16-64 cells.

Morula

Stage where there are 128 cells.

Blastula

Cleavage divisions end with the formation of a:

Blastula/blastoderm

What is the difference between a blastula and blastoderm?

The blastula is the entire early-stage embryo, blastoderm is the layer of cells that makes up the outer layer of the blastula.

What is a blastocoel?

A fluid-filled cavity present inside the blastula

The point at which the control of embryonic development shifts from maternal to the zygotic genome

Mid-blastula transition

When is the mesoderm induced(beginning to form)?

mid-blastula transition

Leading up to the MBT/MZT, cell size ______(increases/decreases) while DNA and cytoplasm _______(increases/decreases).

decreases; increases

MBT/MZT prepares the embryo for _______.

gastrulation

What factor controls the timing of the MBT/MZT?

Ratio of DNA to cytoplasm

What is the effect of higher DNA to cytoplasm ratio on MBT/MZT timing?

Causes it to occur earlier

What events occur during gastrulation?

Cell division is halted, there is extensive cell movement

The formation of the _________ is the first sign that gastrulation is occurring.

Dorsal lip

During gastrulation, how are mesoderm and endoderm cells internalized?

Involution of the blastopore

What is the blastopore?

the first opening that forms in the gastrula during development(next to dorsal lip).

What are 3 reasons extensive cell movement is required during gastrulation?

1. To bring cells to the positions that they need to be:

2. For spatial organization of three cell types (ectoderm, mesoderm, endoderm) into germ layers

3. For specific cell-cell communication events for pattern formation

What structure is formed during neurulation?

Neural tube

The formation of what is first visible sign of segmentation along the A-P axis?

Somites

Where do somites form?

The mesoderm flanking notochord

What is the first sign of neural tube formation?

Neural folds that develop in neural plate

This stage of development is phylotypic, reflects typical chordate body plan, and the AP axis elongates

Pharyngula

What is the main event that occurs in pharyngula?

Organogenesis

_______ __________ are important for establishing body axes.

Maternal determinants

What are maternal determinants?

Proteins and RNAs that are deposited in the egg by the mother during oogenesis.

What occurs in oogenesis?

Egg development

What cells differentiate into the ectoderm?

Animal cell(blastomeres formed at the animal pole)

What cells differentiate into the endoderm?

Vegetal cells(blastomeres formed at the vegetal pole)

What cells differentiate into the mesoderm?

The cells in between the animal and vegetal poles

What 2 mRNAs are localized at the vegetal pole?

Vg-1 and VegT

The animal vegetal axis corresponds roughly to what future axis?

Anterior-posterior

Which experimental technique would allow you to visualize localization of Vg-1 and VegT at the vegetal pole?

In situ hybridization

What is the function of Vg-1?

TGFb signaling protein

What is the function of VegT?

Transcription factor

What would be the result of removing VegT and Vg-1 mRNAs from the embryo?

The embryo would develop with no polarity, and only the ectoderm would form.

What are triploblasts?

Body is derived from 3 germ layers, includes all multicellular organisms except for sponges and coelenterates

This germ layer develops into the skin and nervous system.

Ectoderm

This germ layer develops into the bone, muscle, heart & circulatory system, and kidneys.

Mesoderm

This germ layer develops into the gut and associated organs.

Endoderm

What is fate mapping?

Technique that labels specific cells and follows them to trace which cells and regions of the embryo they give rise to

What experimental technique can we use to determine if a cell’s fate has been specified?

Explanting it: removing a particular cell out of its environment and place it in a neutral environment. If the cell continues to develop according to its normal fate, then its fate has been specified.

What does it mean that cells are autonomously specified?

They have the information to follow their developmental path even if removed from their normal context

What maternal determinant specifies the formation of the endoderm?

VegT

What maternal determinant specifies the formation of the ectoderm?

Foxl1e

Fill in the blank about mesoderm cells: They are found in explants of _____ blastula cells taken from the ______ of animal and vegetal hemispheres

late; margin

Explants taken from which regions will develop into mesoderm cells?

2 and 3

What experiment proved that mesoderm cells are induced by cell to cell communication between animal and vegetal cells?

Mixing animal cap and vegetal cells in explant experiments resulted in mesoderm cell formation

Which is true: Animal cells produce signal and induce vegetal cells to become mesoderm. OR Vegetal cells produce signal and induce animal cells to become mesoderm

Vegetal cells produce signal and induce animal cells to become mesoderm

When animal cells were labeled in early embryo, what tissues were the label found in later?

Ectoderm, mesoderm

True or false: Early in development, animal cells are specified and determined (committed) to become ectoderm cells

False; animal cells are not determined and can be induced to become mesoderm cells.

Can the vegetal signal induce animal cells from a distance?

Yes

What are nodals and what protein family do they belong to?

signals that induce mesoderm; TGF-β family proteins

What is the TGF-β family?

Large and highly conserved family of signaling proteins that are secreted from cells that produce them

Give 4 examples of proteins in the TGF-β family.

Nodal, Nodal-related proteins, Bone Morphogenetic Proteins (BMPs), and Activin