Dev Bio 09 2021 (Exam Study Guide)

Study Guide - Smart Notes

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Developmental Biology: Key Concepts and Processes

Mesenchymal Cells

Mesenchymal cells are a type of embryonic cell characterized by their ability to migrate and differentiate into various cell types.

Definition: Embryonic cells that are unconnected, independent, and capable of migration.
Contrast: Unlike epithelial cells, which are tightly connected, mesenchymal cells are loosely associated.
Example: Mesenchymal stem cells can differentiate into bone, cartilage, and fat cells.

Theories of Tissue and Organ Formation

During development, tissues and organs are formed through specific processes.

Epigenesis: The theory that tissues and organs are formed de novo during development.
Preformation: The outdated idea that organisms develop from miniature versions of themselves.
Phlogiston: Not relevant to developmental biology; historical concept in chemistry.

Homologous and Analogous Structures

Structures in different species can be classified based on their evolutionary origin.

Homologous Structures: Derived from the same progenitors; indicate common ancestry.
Analogous Structures: Similar function but different evolutionary origins.
Example: The wings of birds and the arms of humans are homologous.

Teratogens

Teratogens are agents that disrupt normal development, often causing birth defects.

Definition: Exogenous agents that disrupt development.
Mechanism: Can interfere with DNA replication, transcription, or cell signaling.
Example: Thalidomide is a well-known teratogen.

Gene Expression Regulation

Gene expression is tightly regulated during development, often by transcription factors and enhancers.

Enhancers: DNA sequences that increase transcription when bound by specific proteins.
Promoters: DNA regions where transcription begins.
Equation:

Alternative Splicing

Alternative splicing allows a single gene to produce multiple mRNA variants.

Definition: The process by which different exons are joined to produce diverse mRNAs.
Significance: Increases protein diversity.
Example: Over 70% of human genes undergo alternative splicing.

Cadherins

Cadherins are calcium-dependent proteins involved in cell adhesion.

Function: Mediate cell-cell adhesion, crucial for tissue formation.
Types: E-cadherin (epithelial), N-cadherin (neural), P-cadherin (placental).
Example: Loss of cadherin function can lead to cancer metastasis.

Induction and Cell Signaling

Induction refers to the process by which one group of cells influences the development of another.

Mechanism: Often mediated by signaling molecules such as growth factors.
Example: The notochord induces neural tube formation in vertebrates.

Gametogenesis in Humans

Gametogenesis is the process of forming gametes (egg and sperm cells).

Egg Production: Eggs are only generated before birth in humans.
Fertilization: Normally occurs in the fallopian tube.
Capacitation: Sperm undergo changes to become capable of fertilizing the egg.

Polyspermy Prevention

Polyspermy, the fertilization of an egg by multiple sperm, is prevented by changes in the egg membrane.

Mechanism: Depolarization of the egg membrane and cortical granule reaction.
Significance: Ensures normal development by preventing extra sets of chromosomes.

Cleavage and Gastrulation

Cleavage is the series of rapid cell divisions following fertilization; gastrulation is the process forming the three germ layers.

Cleavage: Increases cell number without increasing embryo size.
Gastrulation: Cells move to form ectoderm, mesoderm, and endoderm.
Example: Gastrulation is a critical step in all animal development.

Model Organisms in Developmental Biology

Model organisms like Caenorhabditis elegans are used for studying development due to their simplicity and genetic tractability.

Advantages: Short embryonic development, transparent body, well-characterized genetics.
Application: Used to study cell lineage and gene function.

Axis Formation and Patterning

Axis formation establishes the body plan of the embryo, including anterior-posterior and dorsal-ventral axes.

Key Determinants: Genes and signaling molecules (e.g., Wnt, Sonic Hedgehog).
Example: The bicoid gene in Drosophila determines anterior structures.

Extraembryonic Membranes

Extraembryonic membranes, such as the amnion, protect and nourish the embryo.

Amnion: Forms a fluid-filled cavity around the embryo in vertebrates.
Function: Provides mechanical protection and prevents desiccation.

Placenta Structure and Function

The placenta is a vital organ for fetal development, facilitating nutrient and gas exchange.

Formation: Formed by trophoblast cells and maternal tissues.
Functions: Gas exchange, nutrient transfer, hormone production, immune protection.
Equation:

Neural Tube Patterning

The dorsal-ventral polarity of the neural tube is controlled by gradients of signaling molecules.

Key Molecules: Wnt, Sonic Hedgehog, TGF-β proteins.
Significance: Determines the fate of neural progenitor cells.

Somite Development

Somites are blocks of mesoderm that give rise to skeletal muscle, vertebrae, and dermis.

Function: Segmental organization of the body plan.
Example: Somites do not contribute to kidney development.

Gut Development

The gut is formed from the endoderm and undergoes complex morphogenesis.

Origin: Derived from the lateral plate mesoderm and endoderm.
Significance: Proper gut formation is essential for nutrient absorption.

Sex Determination and Duct Development

Sex determination involves the differentiation of reproductive organs and ducts.

Wolffian Duct: Develops into male reproductive organs in the presence of testosterone.
Müllerian Duct: Develops into female reproductive organs unless inhibited.

Cell Aging

Cell aging is promoted by various factors, including oxidative stress and changes in DNA methylation.

Mechanisms: Reactive oxygen species, telomere shortening, epigenetic changes.
Significance: Aging affects tissue regeneration and function.

Metamorphosis in Amphibians

Metamorphosis is induced by hormones such as thyroid hormone and signaling molecules.

Key Inducers: 3,5-diiodothyronine, thyroid hormone, Sonic Hedgehog.
Example: Tadpole to frog transformation is regulated by thyroid hormone.

Summary Table: Homologous vs. Analogous Structures

Feature	Homologous Structures	Analogous Structures
Origin	Common ancestor	Different ancestors
Function	May differ	Similar
Example	Human arm, bird wing	Bird wing, insect wing

Summary Table: Extraembryonic Membranes

Membrane	Function	Present in
Amnion	Protects embryo	Reptiles, birds, mammals
Chorion	Gas exchange	Reptiles, birds, mammals
Yolk sac	Nutrient supply	All vertebrates

Additional info: Some explanations and definitions have been expanded for clarity and completeness, based on standard developmental biology knowledge.