Comprehensive Cell Differentiation, Development, and Embryogenesis in Biology

Gene expression

Controls cell specialization.

Transcription

The process of making RNA from DNA.

Post-transcriptional regulation

Includes the translation of RNA into proteins.

Control Regions

Promoters and enhancers that regulate 'when' and 'where' a gene is on.

Chromatin State

Heterochromatin is tightly folded (genes off), while euchromatin is open (genes can be on).

Signal Transduction

External signals travel through the cell membrane to the nucleus.

Outside Chemicals

Direct stimulation by substances like steroids.

Self-Stimulation

A positive feedback loop where a gene's product ensures its own continued production, locking in the cell's identity.

Hox Genes

Specify regional identity; Controls the body plan along an axis (pp. 3-4).

Oct-4

Undifferentiated cell marker; Found in the Inner Cell Mass (ICM) of blastocysts (p. 4).

Sonic Hedgehog (SHH)

Morphogenic signaling; Involved in brain, spinal cord, and limb development (p. 4).

Wnts

Body axis specification; Uses β-catenin signaling; lacks lead to dorsal defects (p. 4).

Notch

Cell-to-cell contact; A transmembrane trigger involved in carcinogenesis (p. 5).

Hematopoietic System

Different growth factors (like EPO or Interleukins) drive stem cells to become specific blood cells like RBCs or Lymphocytes.

Neural Crest

Often called the 'fourth germ layer,' these migratory cells form everything from pigment cells to parts of the nervous system.

Muscles

Myogenic factors like MyoD and myogenin drive mesoderm cells to become skeletal muscle.

Apoptosis

Programmed cell death characterized by blebbing and DNA fragmentation. It is often triggered by TNF (Tumor Necrosis Factor).

What is transdifferentiation?

It is the process where one differentiated cell type changes into another under specific conditions.

Can gene activity be permanent?

No, gene activity isn't always permanent.

What is an example of transdifferentiation?

An adrenal medulla cell can change into a sympathetic neuron.

Proliferation

Rapid cell division (cleavage).

Shape Change

Driven by internal structures (e.g., apical constriction).

Movement

Cells migrating to new locations.

Communication

Signaling between cells to coordinate growth.

Apoptosis

Programmed cell death to sculpt tissues.

Adhesion Molecules

Key types include Cadherins (calcium-dependent), Integrins (cell-matrix), Selectins, and the Immunoglobulin Superfamily.

Junction Types

Cells use Tight Junctions (sealing), Gap Junctions (communication), Desmosomes, and Adherens Junctions to stay connected.

Significance of Adhesion

Adhesion is critical for every major step: cleavage, compaction into a morula, blastulation, and gastrulation.

Cell Attachment

Cells don't just float; they must attach to like-cells to maintain structure and convey positional information.

Isolecithal

Small, even yolk (Humans, Sea Urchins)

Mesolecithal

Moderate yolk at the vegetal pole (Amphibians)

Macrolecithal (Telolecithal)

Large yolk (Birds, Fish)

Holoblastic

Complete division (e.g., radial, spiral, or rotational in mammals)

Meroblastic

Incomplete division due to heavy yolk (e.g., discoidal in birds)

Invagination

Infolding of a cell sheet (like poking a balloon).

Ingression

Individual cells migrating into the interior.

Involution

An expanding sheet rolls over an internal surface.

Delamination

One sheet splits into two parallel sheets.

Epiboly

A sheet spreads to cover the entire embryo surface.

Convergent Extension

Cells rearrange to make a cluster longer and thinner.

Cleavage

Characterized by rapid DNA synthesis and mitotic division without actual growth in embryo mass (p. 6).

Blastulation

Formation of a fluid-filled cavity (blastocoel), driven by the sodium-potassium pump and tight junctions (pp. 7-8).

Neurulation

The formation of the neural tube, driven by cell shape changes (apical constriction) and specific Cell Adhesion Molecules (CAMs) like N-cadherin (pp. 11-12).

In vitro oocyte maturation (IVM)

Harvesting and maturing oocytes outside the ovary.

In vitro fertilization (IVF)

Fertilizing oocytes with sperm in a laboratory setting.

Intracytoplasmic sperm injection (ICSI)

Direct injection of sperm into an oocyte's cytoplasm.

Cloning and Transgenic organisms

Creating genetically identical copies or organisms with foreign DNA (e.g., kittens that glow with Red Fluorescent Protein).

Stem Cells

Research into stem cell development and therapeutic applications.

What is the placenta?

Tissues that are designed during development for protection of embryo/fetus, gas exchange, and exchange of nutrients/wastes, which are ultimately sloughed off as 'afterbirth' after the fetus is born.

What is the origin of the placenta?

The fetus (and the mother perhaps).

How many extraembryonic membranes are formed from the embryo?

4 (Amnion, chorion, allantois, yolk sac).

What determines how much is sloughed off as 'afterbirth'?

The type of attachment of chorion to mother.

What are the types of placental attachments?

1) Epitheliochorial (ex. pig), 2) Syndesmochorial (ex. deer, cattle), 3) Endotheliochorial (ex. cats, dogs), 4) Hemochorial (ex. humans).

What is somatopleure?

Ectoderm + somatic mesoderm.

What is splanchnopleure?

Endoderm + splanchnic mesoderm.

What does the amnion consist of?

Somatopleure (internal lining with ectoderm).

What is the function of the amnion?

Holds embryo/fetus in a fluid-filled environment to prevent friction.

What does the chorion consist of?

Somatopleure (internal lining with mesoderm).

What is the function of the chorion?

Outermost layer of extraembryonic membranes in most species; exchange occurs across this membrane (if present).

What does the yolk sac consist of?

Splanchnopleure (internal lining with endoderm).

What are the functions of the yolk sac?

Source of food (in chicken), source of primordial germ cells (endoderm), and source of some blood cells (mesoderm).

What does the allantois consist of?

Splanchnopleure (internal lining with endoderm).

What is the function of the allantois?

Exchange with the environment; nitrogenous waste products are stored here.

What is the size of a child on day 28 of development?

About 4 mm, the size of a grain of rice.

What structures begin to form from the mesoderm during development?

The heart and circulatory system.

What does the endoderm begin to form?

The linings of the lungs, intestines, and urinary systems.

What unique developments are involved in reproductive technology?

In vitro oocyte maturation (IVM), in vitro fertilization (IVF), ICSI, cloning, and transgenic organisms.

What is IVM?

In vitro oocyte maturation.

What is IVF?

In vitro fertilization.

What is ICSI?

Intracytoplasmic sperm injection, where sperm or parts of sperm are injected into the cytoplasm of a secondary oocyte.

Who was the first successful test-tube baby?

Louise Joy Brown, born on July 25, 1978.

When was the first US test-tube baby born?

Elizabeth Carr on December 28, 1991.

What is parthenogenesis?

A form of asexual reproduction where offspring are produced from an unfertilized egg.

Can parthenogenesis occur naturally in mammals?

No known cases exist in the wild.

Who successfully induced parthenogenesis in a rabbit?

Gregory Pincus in 1936.

What was significant about Kaguya the mouse?

It was created using parthenogenesis and had two parents of the same sex.

What is cloning in the context of developmental biology?

Taking a nucleus from a cell and placing it into an enucleated oocyte.

What were the problems associated with Dolly the sheep?

Dolly died of lung cancer and required shutting down adult gene expression.

Who was Ian Wilmut?

The scientist who created Dolly the sheep.

What did Korean scientist Kong Il-keun achieve in 2007?

He made kittens that expressed Red Fluorescent Protein (RFP).