Comparative Embryonic Development: Principles of Development

Generated for Mid-Terms at Saint Louis University.

Development

• the process by which organisms grow and develop from a single cell into a complex multicellular organism, involving cellular differentiation and morphogenesis.

• Series of progressive changes in an individual from its beginning to maturity

• begins when a fertilized egg divides mitotically

• Specialization occurs as a hierarchy of developmental “decisions”

Gamete Formation

• the process by which specialized reproductive cells, or gametes, are produced in organisms. This involves meiosis, where diploid cells undergo division to form haploid sperm and egg cells, ensuring genetic diversity in offspring.

• Sperm and eggs form, mature

Fertilization

• Egg and Sperm unite

Cleavage

• a series of rapid cell divisions that occur immediately after fertilization, resulting in the formation of a multicellular embryo. This process leads to the formation of the blastula stage, where cells begin to differentiate.

• Zygote subdivides, determinants partitioned in blastomeres

Gastrulation

• Germ layers form

• the phase in embryonic development where the blastula reorganizes into a multilayered structure called the gastrula. This process establishes the three primary germ layers: ectoderm, mesoderm, and endoderm, which will give rise to all tissues and organs.

Organogenesis

• the process by which the three germ layers develop into the organs and structures of the body. This phase involves the differentiation and organization of cells into functional tissues and organs.

• Body organs form, cells interact, differentiate

Growth

• the process of increasing in size and mass, involving cell division and differentiation. This phase occurs after organogenesis and is crucial for the proper development of the organism.

• Organs increase in size and function as the organism matures. Adult body form is attained

Fertilization

• the union of sperm and egg to form a zygote, initiating embryonic development. This process involves the fusion of genetic material from both parents, establishing the genetic blueprint for the new organism.

• initial event in development in sexual reproduction

• Contact and recognition between the egg and sperm

Research Done on Marine Invertebrates

• Release enormous numbers of sperm in the ocean to fertilize eggs

• Many eggs release a chemical molecule to attract sperm, enhancing the likelihood of fertilization. This strategy increases reproductive success in unpredictable environments.

Cortical Granule

• small membrane-bound organelles in eggs that release enzymes during fertilization. They help prevent polyspermy by modifying the egg's outer layer, ensuring that only one sperm can fertilize the egg.

Vitelline Envelope

• a thick protective layer surrounding the egg that plays a crucial role in fertilization. It interacts with sperm and is involved in the prevention of polyspermy.

• This envelope is important for species-specific recognition and binding of sperm, ensuring successful fertilization.

Yolk Granule

• nutrient-rich structures within the egg that provide essential nourishment for the developing embryo. They play a critical role in supporting early development before the embryo can rely on external sources for nutrition.

• These granules store lipids, proteins, and carbohydrates essential for embryonic growth.

Jelly Layer/Coat

• a gelatinous layer surrounding the egg that provides protection and aids in fertilization. It is involved in attracting sperm and can help prevent polyspermy.

Plasma Membrane

• a selectively permeable barrier that surrounds the egg, controlling the movement of substances in and out. It plays a key role in maintaining the internal environment of the egg and is involved in the fusion of sperm during fertilization.

• Essential for cellular communication and signaling, ensuring proper development of the embryo.

Sperm Nucleus

• the genetic material from the sperm that combines with the egg's nucleus during fertilization. It contains half of the genetic information needed to form a new organism, contributing to the genetic diversity of the offspring.

• It carries paternal DNA and is crucial for the formation of a zygote, establishing the genetic identity of the embryo.

Acrosome

• a membrane-bound structure at the tip of a sperm that contains enzymes necessary for penetrating the egg's jelly layer and plasma membrane during fertilization. It plays a critical role in the sperm's ability to fertilize the egg.

• Releases these enzymes to facilitate the fusion of sperm and egg, ensuring successful fertilization.

Egg-Recognition Proteins/Sperm-Binding Receptors

• Proteins located on the surface of the egg that help recognize and bind to sperm. They play a vital role in species-specific fertilization by ensuring that only compatible sperm can attach and initiate fertilization, thereby promoting successful reproduction.

• These proteins are crucial for preventing polyspermy, ensuring that only one sperm fertilizes the egg, thus maintaining the proper genetic balance in the resulting zygote.

Fertilization Membrane/Envelope

• a protective barrier formed around the egg after fertilization. It prevents additional sperm from entering, thus ensuring that only one sperm fertilizes the egg and maintaining the genetic integrity of the zygote.

Acrosomal Process

• a projection that forms from the acrosome of a sperm during fertilization. It helps the sperm penetrate the egg's protective layers, facilitating the fusion with the egg's plasma membrane.

• This structure extends from the acrosome and aids in the sperm's ability to deliver its genetic material into the egg, playing a crucial role in successful fertilization.

Basal Body (Centriole)

• the structure that anchors the microtubules of cilia and flagella, playing a critical role in the formation and organization of these organelles. It is essential for cell movement and signaling.

• The basal body is a cylindrical structure that originates from the centriole and serves as the foundation for cilia and flagella. It is crucial for the assembly and stability of these organelles, ensuring proper function in motility and sensory roles.

Sperm Head

• the part of the sperm that contains the nucleus and genetic material. It is responsible for delivering DNA to the egg during fertilization and is covered by the acrosome, which aids in penetrating the egg's protective layers.

• The sperm head is the anterior part of the sperm cell, housing the genetic information needed for fertilization. It plays a vital role in the reproductive process by facilitating the fusion of sperm and egg.

Hydrolytic Enzymes

• enzymes that break down biomolecules by hydrolysis, facilitating digestion and cellular processes. They are crucial for degrading proteins, carbohydrates, and lipids in various biological contexts.

• These enzymes are secreted by lysosomes and play a key role in cellular digestion and nutrient absorption.

• Hydrolytic enzymes are essential for breaking down complex biomolecules into simpler forms, allowing cells to utilize nutrients effectively. They function in various cellular processes, including the degradation of macromolecules within lysosomes.

Actin Filaments (Fertilization)

• Are dynamic structures composed of actin protein that play a crucial role during fertilization by facilitating the movement and shape changes of the sperm and egg. They are essential for processes such as sperm motility and the formation of the fertilization cone, aiding in the fusion of gametes.

Fused Plasma Membrane (Fertilization)

• the process during fertilization where the sperm and egg membranes merge, allowing the sperm to deliver its genetic material into the egg. This fusion is essential for initiating the developmental processes that lead to embryo formation.

Acrosomal Reaction

• a process where the sperm's acrosome releases enzymes that help penetrate the egg's protective layers, facilitating fertilization.

Sperm Plasma Membrane

• It also helps maintain the sperm's structural integrity and regulates the entry of ions and molecules necessary for sperm function.

• The sperm plasma membrane is a lipid bilayer that surrounds the sperm cell, providing protection and playing a vital role in sperm-egg interaction during fertilization.

• A fast block to polyspermy

Perivitelline Spaces

• the fluid-filled spaces between the vitelline membrane and the egg plasma membrane, important for preventing polyspermy and facilitating fertilization.

• These spaces play a crucial role in the fertilization process by creating a barrier that prevents multiple sperm from entering the egg, ensuring successful fertilization.

Egg Cytoplasm

• the cytoplasmic material within the egg cell that contains organelles, nutrients, and genetic material necessary for early embryonic development. It plays a crucial role in supporting the developing embryo after fertilization.

Cells of Corona Radiata

• the layer of follicular cells that surround the egg, providing nutrients and support during oocyte maturation and fertilization.

Zona Pellucida

• a glycoprotein layer surrounding the egg that plays a critical role in sperm binding and fertilization, acting as a protective barrier before implantation.

Ovum

• the female gamete or egg cell, which is involved in reproduction and contains half of the genetic material necessary for the formation of a new organism.

Female Pronucleus

• the nucleus of the ovum after fertilization that contains the female genetic material and is involved in the formation of the zygote.

Male Pronucleus

• the nucleus of the sperm after fertilization that contains the male genetic material and contributes to the formation of the zygote.

Zygote

• the initial cell formed when a new organism is created through the fertilization of an ovum by a sperm, containing genetic material from both parents.

• Early Cleavage Stages

• Blastula: a hollow sphere of cells formed during early embryonic development, following the cleavage of the zygote and preceding gastrulation.

• Establish Polarity and Body Axes: the process during embryonic development that determines the organization of the body plan, including anterior-posterior and dorsal-ventral axes.

Gastrulation

• the phase in embryonic development following the blastula stage, during which the single-layered blastula reorganizes into a multilayered structure called the gastrula, establishing the primary germ layers.

Body Plan (Segmentation)

• the arrangement of body parts and structures in an organism, often involving repeated segments, which can lead to the development of specialized structures and functions.

• Involves Neurulation in vertebrates

Morphogenesis

• the biological process that causes an organism to develop its shape, involving the organization and spatial distribution of cells during embryonic development.

• Organogenesis

Cleavage

• the series of rapid cell divisions that follow fertilization, resulting in the formation of a multicellular embryo without significant growth.

Blastomeres

• the individual cells that result from the cleavage of a fertilized egg, which eventually form the blastula during early embryonic development.

Morula

• a solid ball of cells formed by the cleavage of a fertilized egg before it develops into a blastocyst.

Isolecithal

• a type of egg with a small amount of evenly distributed yolk, allowing for equal cleavage in early development.

• This type of egg is found in species such as sea urchins and some mammals, facilitating uniform cell division during cleavage.

Mesolecithal

• a type of egg containing moderate amounts of yolk, which is unevenly distributed, resulting in unequal cleavage. This type of egg is typically found in species like frogs, where the yolk influences the distribution of cells during early development.

• a type of egg with moderate yolk that leads to unequal cleavage, commonly found in amphibians.

Telolecithal

• a type of egg with a large amount of yolk concentrated at one end, resulting in significant unequal cleavage. This type is commonly found in reptiles and birds, where the yolk influences early developmental patterns.

• a type of egg that has a large yolk mass at one pole, leading to substantial asymmetry in cleavage patterns, typical in species such as chickens and turtles.

Holoblastic

• Cleavage extends entire length of egg

• Egg does not contain a lot of yolk

• a type of cleavage where the entire egg is divided into smaller cells, typical in isolecithal and mesolecithal eggs. This process allows for complete division of the fertilized egg, leading to uniform cell sizes.

• (e.g, Mammals, Sea Stars, Worms)

Meroblastic

• Cells divide sitting on top of yolk

• Too much yolk and yolk can’t divide

• a type of cleavage where only part of the egg is divided due to a large yolk mass, common in telolecithal eggs. This results in incomplete division, typically seen in reptiles, fish and birds.

Blastulation

• Cleavage creates a cluster of cells called Blastula

• Cells are arranged around a fluid-filled cavity called the blastocoel

• First germ layer forms

Blastula

• When cleavage creates a cluster of cells

• A hollow sphere of cells formed during the early stages of embryonic development, resulting from cleavage and preceding gastrulation.

Blastocoel

• The fluid-filled cavity inside the blastula, providing space for cell movement and differentiation during early embryonic development.

Gastrulation

• Results in the formation of a second germ layer

• Involves an invagination process that leads to the development of the digestive tract and other organ systems.

• Formation of gastrocoel and blastopore

• Outer layer of ectoderm and an inner layer of endoderm

• Formation of mesoderm as a third germ layer.

• Animals with two germ germ layer

Blastopore

• The opening that forms during gastrulation, leading to the development of the digestive system in the embryo.

Diploblastic

• Organisms with two germ layers: ectoderm and endoderm.

Triploblastic

• Organisms with three germ layers: ectoderm, mesoderm, and endoderm.

• Most animals add a 3rd germ layer

Ectoderm

• Epithelium and nervous system

Endoderm

• Epithelial lining of the digestive and respiratory tract, liver, pancreas

Mesoderm

• Muscular system, reproductive system, bone, kidneys, blood, and notochord

Neurulation

• Formation of neural tube from ectoderm of ectoderm of the embryo

• chordates and vertebrates embryos

• The embryo at this stage is termed the neurula

• The process during embryonic development where the neural tube forms from the ectoderm, leading to the development of the central nervous system.