Embryology Research in the 19th Century
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Questions and Answers

What was the primary focus of embryological research by the end of the 19th century?

  • Descriptive anatomy
  • Environmental influences
  • Physiological mechanisms (correct)
  • Evolutionary relationships

Entwicklungsmechanik aimed to solely study anatomy and evolution.

False (B)

What is the term often used to translate Entwicklungsmechanik?

developmental mechanics / causal embryology

Experimental embryology focuses on how cells order themselves into tissues and ______.

<p>organs</p> Signup and view all the answers

Match the research area of experimental embryology with its primary focus:

<p>Environmental Developmental Biology = How forces outside the embryo influence its development Developmental Mechanics of Cell Specification = How forces within the embryo cause the differentiation of its cells</p> Signup and view all the answers

Which of the following cellular processes contribute to morphogenesis?

<p>All of the above (D)</p> Signup and view all the answers

Neurons typically divide frequently after birth to regenerate and maintain brain tissue.

<p>False (B)</p> Signup and view all the answers

What are the two major types of cell arrangements observed in embryos?

<p>Epithelial and Mesenchymal</p> Signup and view all the answers

If the intestine generated more cells than it sloughed off, it could produce ______.

<p>tumors</p> Signup and view all the answers

Match the cell type with its arrangement:

<p>Epithelial cells = Tightly connected sheets or tubes Mesenchymal cells = Unconnected, independent units</p> Signup and view all the answers

Which of the following is an example of environmental sex determination?

<p>Sex determination in Bonellia viridis based on larval settlement location. (A)</p> Signup and view all the answers

The sex of alligator embryos is determined genetically by sex chromosomes.

<p>False (B)</p> Signup and view all the answers

What did August Weismann observe regarding butterflies?

<p>Butterflies hatched during different seasons exhibited different colorations. (A)</p> Signup and view all the answers

What term is used to describe phenotypic variations caused by environmental differences?

<p>morphs</p> Signup and view all the answers

Which environmental factors control the change from spring to summer morph in the European map butterfly (Araschnia levana)?

<p>Changes in day length and temperature. (B)</p> Signup and view all the answers

The moth Nemoria arizonaria has caterpillars that resemble oak catkins when they hatch in the ______.

<p>spring</p> Signup and view all the answers

Altering environmental parameters can never alter the development of an organism.

<p>False (B)</p> Signup and view all the answers

According to Ferguson and Joanen's study, at what temperature do alligator eggs produce female alligators?

<p>30°C or lower (B)</p> Signup and view all the answers

In Baltzer's experiment with Bonellia viridis, what happened when a larva landed on a female's proboscis?

<p>It developed into a male.</p> Signup and view all the answers

Match the following structures with their corresponding sex outcome in Alligator:

<p>Eggs incubated at 30°C or lower = Female Eggs incubated at 34°C or higher = Male</p> Signup and view all the answers

What major role do cell surface proteins play during morphogenesis?

<p>Forming the structure of tissues and organs (A)</p> Signup and view all the answers

Townes and Holtfreter's experiment involved combining cell suspensions from different bacterial species to observe aggregation.

<p>False (B)</p> Signup and view all the answers

According to Townes and Holtfreter's experiment, what happened when epidermal and mesodermal cells were mixed?

<p>Epidermal cells moved to the periphery, while mesodermal cells moved to the inside.</p> Signup and view all the answers

Townes and Holtfreter used ______ solutions to dissociate amphibian embryo cells into single cells.

<p>alkaline</p> Signup and view all the answers

Match the cell type with its final position in the re-aggregated cell mixture:

<p>Epidermal Cells = Periphery of the aggregate Mesodermal Cells = Inside of the aggregate Endodermal cells = Migrated centrally w.r.t. mesoderm</p> Signup and view all the answers

What was a key observation from Townes and Holtfreter's re-aggregation experiments?

<p>Re-aggregated positions of cells mirrored their embryonic positions. (D)</p> Signup and view all the answers

Differential cell affinity suggests that all cell types have the same set of surface proteins.

<p>False (B)</p> Signup and view all the answers

What did Townes and Holtfreter observe regarding tissue type envelopment during cell re-aggregation?

<p>One tissue type often completely enveloped the other.</p> Signup and view all the answers

What is the term for the ability of embryonic cells to alter their fates to compensate for missing parts?

<p>Conditional specification (B)</p> Signup and view all the answers

August Weismann's Germ Plasm Theory proposed that all cells of the embryo receive the same chromosomal determinants.

<p>False (B)</p> Signup and view all the answers

Name two of the experimental techniques pioneered during the testing of the Germ Plasm Theory.

<p>defect experiment, isolation experiment</p> Signup and view all the answers

Wilhelm Roux performed experiments on frog embryos and obtained ______ after destroying some cells.

<p>half-blastulae</p> Signup and view all the answers

Match the scientist with their experimental finding:

<p>Wilhelm Roux = Obtained half-blastulae in frog embryos Hans Driesch = Demonstrated regulative development in sea urchin embryos August Weismann = Proposed the Germ Plasm Theory</p> Signup and view all the answers

What did Hans Driesch observe when he separated sea urchin blastomeres from a 2-cell embryo?

<p>Each blastomere developed into a complete larva. (B)</p> Signup and view all the answers

Wilhelm Roux's experiments supported the idea of regulative development.

<p>False (B)</p> Signup and view all the answers

What type of development did Driesch's sea urchin embryo experiments demonstrate?

<p>regulative development</p> Signup and view all the answers

In Driesch's recombination experiment, he reshuffled the nuclei of sea urchin embryos by compressing them between two ______.

<p>glass plates</p> Signup and view all the answers

According to Driesch, what determines the fate of a nucleus in the early sea urchin embryo?

<p>The relative position of the blastomere within the embryo (C)</p> Signup and view all the answers

The transplantation experiment involves destroying a portion of the embryo and observing the resulting development.

<p>False (B)</p> Signup and view all the answers

What did Roux conclude from his hot needle experiment on frog embryos?

<p>The frog embryo was a mosaic of self-differentiating parts.</p> Signup and view all the answers

According to the Germ Plasm Theory, only cells destined to become ______ retained all determinants.

<p>gametes</p> Signup and view all the answers

What causes the third division to be meridional when Driesch compressed early embryos?

<p>Compression between two glass plates (C)</p> Signup and view all the answers

Match the term with its definition:

<p>Defect Experiment = A portion of the embryo is removed. Recombination Experiment = Replacing one part with a part from a different region. Isolation Experiment = A portion of the embryo is destroyed.</p> Signup and view all the answers

What did Malcolm Steinberg propose in 1964?

<p>The differential adhesion hypothesis (C)</p> Signup and view all the answers

According to Steinberg's thermodynamic model, cells interact to form an aggregate with the largest interfacial free energy.

<p>False (B)</p> Signup and view all the answers

What type of binding is exhibited by cadherins when they bind to the same type of cadherin on another cell?

<p>homophilic binding</p> Signup and view all the answers

Cadherins are anchored into the cell by a complex of proteins called ______.

<p>catenins</p> Signup and view all the answers

Match the following cadherins with their primary expression location:

<p>E-cadherin = Epithelial tissues P-cadherin = Trophoblast cells and uterine wall epithelium N-cadherin = Neural plate, neural tube, and mesodermal tissues EP-cadherin (C-cadherin) = Embryonic tissues, especially Xenopus blastula blastomeres</p> Signup and view all the answers

According to Foty et al (1996), what is needed for cell sorting to occur?

<p>Difference in strengths of adhesion between cell types (A)</p> Signup and view all the answers

E-cadherin is expressed solely on adult neural tissues.

<p>False (B)</p> Signup and view all the answers

What process is facilitated by P-cadherin in mammalian embryos?

<p>implantation</p> Signup and view all the answers

The cadherin-catenin complex forms classical ______ junctions that connect epithelial cells together.

<p>adherens</p> Signup and view all the answers

Which cadherin is prominent in the neural plate, neural tube, and mesodermal tissues?

<p>N-cadherin (C)</p> Signup and view all the answers

Cells with E-cadherin will stick best to cells containing N-cadherin.

<p>False (B)</p> Signup and view all the answers

In the gastrula of the frog Xenopus, which cadherin is expressed by the neural tube?

<p>N-cadherin</p> Signup and view all the answers

According to the thermodynamic model, the early embryo exists in an ______ state until gene activity changes cell surface molecules.

<p>equilibrium</p> Signup and view all the answers

The cells rearrange themselves into most what to form an aggregate?

<p>thermodynamically stable pattern (C)</p> Signup and view all the answers

The trophoblast cells have several adhesion molecules, E-cadherins, P-cadherins recognise similar ______ on uterine cells.

<p>cadherins</p> Signup and view all the answers

Flashcards

Experimental Embryology

A branch of biology that studies the processes and mechanisms of embryonic development through experimentation.

Entwicklungsmechanik

A German term meaning 'developmental mechanics' or 'causal embryology' that seeks to understand developmental processes.

Morphogenesis

The biological process that causes an organism to develop its shape and structure.

Environmental Developmental Biology

The study of how external forces affect embryonic development.

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Cell Specification

The process by which cells differentiate into specific types during development.

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Environmental cues

External factors that influence the developmental processes of an organism.

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Bonellia viridis

A type of echiuroid worm whose sex determination is influenced by larval settlement location.

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Sex determination in Bonellia

A process where Bonellia larvae become male or female based on the substrate they settle on.

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Proboscis chemical signals

Substances emitted by the female Bonellia that attract larvae to become males.

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Alligator sex determination

The sex of alligators is determined by the incubation temperature of eggs.

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Norms of reaction

Phenotypic variations in organisms caused by environmental differences.

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Seasonal morphs

Different phenotypes expressed by an organism depending on the season.

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Araschnia levana

A butterfly species with morphs that change from bright to dark based on seasonal conditions.

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Nemoria arizonaria adaptations

Moth that changes appearance based on food sources available during different seasons.

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Mitosis Control

The regulation of cell division rates to maintain tissue balance.

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Organ Polarity

The organized arrangement of different tissue types in organs.

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Epithelial Cells

Cells tightly bound together forming sheets or tubes.

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Mesenchymal Cells

Cells that function independently and are unconnected.

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Variations in Morphogenesis

Different cellular processes contributing to shape development.

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Differential cell affinity

The phenomenon where different types of cells have varying tendencies to adhere to one another, influencing tissue organization.

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Cell surface proteins

Proteins present on the cell membrane that determine the cell's interaction with other cells and its environment.

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Townes and Holtfreter experiment

A study in 1955 demonstrating how cells differentiate and arrange themselves based on affinity.

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Re-aggregation of cells

The process where dissociated cells regroup to form structured arrangements; showing affinity and segregation.

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Epidermal and mesodermal interaction

Epidermal cells prefer to be on the outside, while mesodermal cells tend to cluster towards the center when mixed.

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Embryonic position reflection

The final arrangement of cells in aggregates reflects their original positions during early development.

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Alkaline solutions in experiments

Solutions used to dissociate cells for the purpose of studying their aggregation properties.

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Mesoderm migration

The movement of mesodermal cells towards the center when interacting with other types of cells, showcasing their adhesion properties.

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Differential Adhesion Hypothesis

A theory proposing cell sorting based on the strength of cell adhesion.

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Cell Sorting

The process where cells organize into distinct layers based on adhesion strengths.

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Thermodynamic Model

A model explaining cell interactions using thermodynamic principles.

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Centrifugal vs. Centripetal Migration

Cells may migrate to the center or the periphery based on type combinations.

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Hierarchy of Cell Positioning

In cell sorting, A will always be internal to C if A is internal to B and B is internal to C.

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Interfacial Free Energy

Cells rearrange to form aggregates that minimize interfacial energy.

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Cadherins

Calcium-dependent molecules crucial for cell adhesion and tissue integrity.

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Homophilic Binding

Cells stick to other cells with the same type of cadherin.

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Types of Cadherins

Different classes of cadherins exist, such as E-cadherin, P-cadherin, and N-cadherin.

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E-cadherin

A type of cadherin found in early mammalian embryonic cells and later in epithelial tissues.

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N-cadherin

A cadherin type essential for neural tube formation and neural crest cell migration.

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P-cadherin

Cadherin primarily located on trophoblast cells and uterine wall epithelium.

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Cadherin Interaction

Cadherins connect cells and incorporate into a complex affecting adhesion strength.

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Surface Adhesion Differences

Cell types can sort based on varying adhesion molecule levels on their surfaces.

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Cell Adhesion in Development

Differing adhesion levels are crucial for proper embryonic structure formation.

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Conditional specification

The ability of embryonic cells to alter their fates and compensate for missing parts.

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Germ Plasm Theory

The concept that chromosomes carry inherited potentials but not all determinants enter every cell.

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Wilhelm Roux

A scientist who demonstrated that frog embryos are mosaics of self-differentiating parts.

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Isolation experiment

A method where portions of the embryo are removed to study their development.

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Defect experiment

A technique where part of an embryo is destroyed to observe the impact on development.

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Regulative development

Development where isolated blastomeres adjust to form a complete organism rather than a specific part.

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Hans Driesch

A scientist who showed that separated sea urchin blastomeres can each develop into a complete larva.

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Recombination experiment

An experimental technique that observes development after replacing parts of an embryo.

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Meridional cleavage

The type of cleavage that divides the embryo through both poles.

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Equatorial cleavage

The cleavage that divides the embryo horizontally, creating upper and lower cells.

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Cell fate determination

The process where the position and environment of a cell determines its future development.

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Chromosomal determinants

Specific genetic factors on chromosomes that influence cell characteristics and functions.

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Blostomere

An early embryonic cell that can develop into various tissue types under certain conditions.

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Self-differentiation

The process where cells autonomously develop into specific cell types.

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Fate map

A diagram showing the future development paths of cells in an embryo.

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Study Notes

Experimental Embryology

  • Descriptive and evolutionary embryology originated in anatomy.
  • By the late 19th century, physiology also contributed to embryological research.
  • Early questions of "what?" evolved into questions of "how?" in embryology.
  • The focus shifted from simply describing anatomy and evolution to understanding the mechanisms driving development.
  • This led to the study of "developmental mechanics" or "causal embryology," focusing on the molecules and processes causing changes in embryos.
  • Embryologists began to study organ formation (morphogenesis) and cell differentiation.
  • Experimentation was crucial to complement observational studies of embryos.
  • Experimental embryology encompasses three major research programs:
    • How environmental factors outside the embryo influence its development
    • How forces within the embryo cause cell differentiation
    • How cells organize themselves into tissues and organs

Environmental Developmental Biology

  • The developing embryo is not isolated from its environment.
  • In numerous species, environmental cues significantly affect development.
  • Environmental cues/parameters are essential to life-cycle.
  • Altering the environment can change development.

Environmental Sex Determination

  • Sex in the echiuroid worm, Bonellia, is determined by the location the larva settles.
  • Female Bonellia worms are larger (10 cm) and live on the seafloor.
  • Male Bonellia worms are smaller (1-3 mm) and reside within the female's reproductive organs.
  • Larva settling on the female's proboscis become male, potentially due to chemical cues.
  • Lab experiments have reproduced this sex determination in Bonellia.
  • Sex determination in some reptiles, such as alligators, is determined by temperature during incubation.
  • Eggs incubated below 30°C produce females, while eggs incubated above 34°C produce males.

Adaptation of Embryos and Larvae to their Environments

  • Norms of reaction: The range of phenotypic responses possible for a single genotype in different environments.
  • August Weismann noticed variation in butterfly coloring corresponding to seasons.
  • This environmental variation can be mimicked by controlling larval development temperature.
  • Phenotypic variations from environmental differences are termed "morphs".
  • For example, the European map butterfly (Araschnia levana) exibits seasonal color variation (spring=orange, summer=black).
  • This coloration can be mimicked by changing incubation temperatures.
  • The moth Nemoria arizonaria displays a spring and summer morph in relation to the oak flowers/leaves they feed on, and the associated coloration changes
  • Experiments suggest spring morph as the "default" state with the caterpillar's coloration controlled by environmental factors.
  • Thus, what gets inherited is a range of potential phenotypes, and the environment selects the adaptive one for a particular season or habitat.

The Developmental Mechanics of Cell Specification

  • Differentiation is the process of developing specialized cell types.
  • Before full differentiation, a developmental commitment occurs involving cell fate determination.
  • There are two developmental commitment phases:
    • Specification: The fate of a cell is specified and capable of autonomously differentiating even when placed in a neutral environment.
    • Determination: a point of no return for a cell’s fate; a determined cell will differentiate even when transferred to another part of the developing organism.

Modes of Commitment

  • Autonomous specification: Cell fate is determined by the cytoplasmic determinants in the egg and is typically a mosaic pattern of development.
    • Morphogenetic determinants are distributed in the egg cytoplasm, influencing cell types during division.
    • This can be experimentally observed by manipulating a blastomere and seeing what cells or tissue it develops into.
  • Conditional specification: The organism uses regulative development where cell fate is dependent on the cells around it.
  • In isolation experiments, the cells are separated from each other.
    • When a blastomere in a developing embryo is removed that cell or tissue won’t develop in the embryo but the cells and tissues around the removal will continue to develop and continue to make up for the tissue or cell that was removed.
  • Syncytial specification: There is no complete cell division. Nuclei divide, but not the cytoplasm. Cytoplasmic molecules determine fates, like gradients controlling developmental programs.
    • In Drosophila eggs, Bicoid and Nanos molecules are present in gradients and direct different functions relating to position and development, along the anterior/posterior axis.
  • Morphological/Morphogenetic field: A portion of cells with interactions whose position defines their fate.

Morphogenesis and Cell Adhesion

  • Morphogenesis: The processes that organize cells into tissues, organs and structure.

  • Major components involved in morphogenesis relate to how different structures form through development and the mechanisms of adhesion.

  • There are five major questions in relation to morphogenesis.

    • How are tissues formed from cell populations?
    • How are organs structured by tissues?
    • How do organs form in particular locations and does migration occur?
    • How do growth and the processes or cells associated with growth, regulate and function throughout development?
    • How do organs become polarized?

  • Differentiation and formation of cell types and layers is involved in how organs develop, what determines their position and growth.

  • Cell-cell communication, interactions and adhesion are involved with how cells communicate and coordinate to build an organ or even a finger, for example.

  • Cell affinity patterns can change during development and influence the way tissues and cells form in organisms.

  • Different types of cell adhesion patterns occur depending on the type of structure and cell type.

  • Thermodynamic cell interactions: The interaction/relationship of cells in creating tissue during and throughout development.

  • Cadherins are calcium-dependent adhesion molecules critical to cell-cell interactions.

    • Homophilic binding: similar cadherins on adjacent cells bind together.
    • Different cadherins on different cells result in different adhesion potentials and cell types will adhere to similar types of cells.

  • The level and type of cadherins influence how tissues develop and different tissues can have different levels and types of cadherins or even levels of adhesive forces.

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Experimental Embryology PDF

Description

Test your knowledge on embryological research developments by the end of the 19th century. This quiz covers key concepts such as mechanistic developmental biology, experimental embryology, and cellular processes involved in morphogenesis. Dive into the fascinating world of embryology and its historical insights!

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