Lecture 3

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Questions and Answers

What is the function of the chalaza in an egg?

To facilitate fertilization of the ovum

To protect the yolk from damage

To ensure the blastodisc is always oriented on top (correct)

To provide nutrients to the embryo

What is the term for the whitish, sticky jelly-like liquid structure outside the yellow yolk?

Albumin

White yolk (correct)

Egg white

Thicker albumin

What is the term for the region containing the nucleus in a mature ovum?

Blastodisc

Yolk

Active cytoplasm (correct)

Nucleus region

What is the purpose of injecting hormones into hen layers, such as VitaLink PH?

To hasten ovulation and release multiple oocytes Signup and view all the answers

What is the term for the unfertilized structure that will give rise to the chick embryo?

Blastodisc Signup and view all the answers

What is the term for the ovarian follicle/ovum located near the wall of the ovarian epithelium?

Ovarian follicle Signup and view all the answers

What is the term for the structure that will give rise to the chick embryo, not the whole yolk?

Blastoderm Signup and view all the answers

What is characteristic of the oviduct in Aves compared to other vertebrates?

It is longer in proportion to body size Signup and view all the answers

What is the function of the cytoplasmic bridges between cells in spermatogenesis?

To synchronize the maturation of sperm cells Signup and view all the answers

What is the significance of the Type A4 spermatogonia?

They have the option to undergo another round of cell division or undergo apoptosis Signup and view all the answers

What is the purpose of the acrosome cap in spermatozoa?

To aid in fertilization by containing enzymes Signup and view all the answers

How long does it take for spermatids to mature into spermatozoa?

24 days Signup and view all the answers

What is the role of histones in DNA packaging during spermiogenesis?

They are partially replaced by transition proteins Signup and view all the answers

What is the function of the midpiece in spermatozoa?

It is surrounded by mitochondria Signup and view all the answers

What is the consequence of abnormal spermatozoa with acrosomeless defects?

They cannot penetrate the oocyte Signup and view all the answers

Why do species-specific differences occur in the head of spermatozoa?

Due to differences in coat proteins Signup and view all the answers

What is the function of the Golgi apparatus during spermatogenesis?

To form the acrosome cap Signup and view all the answers

What is the significance of the primary spermatocytes in spermatogenesis?

They undergo meiosis to form secondary spermatocytes Signup and view all the answers

What is the duration of egg maturation in amphibians?

3 years Signup and view all the answers

What is the characteristic of the previtellogenic phase in amphibian oocyte maturation?

Increase in mitochondrial number Signup and view all the answers

What is the result of the accumulation of mitochondria in the previtellogenic phase?

Formation of dense body called Balbiani body Signup and view all the answers

What is the purpose of the jelly coat in the frog's oocyte?

To prevent desiccation Signup and view all the answers

What is the blocked stage in amphibian oogenesis, similar to mammals?

Diplotene block Signup and view all the answers

What is the activator of amphibian oogenesis?

Progesterone Signup and view all the answers

What is the purpose of the cortical granules in amphibian oocyte maturation?

To prevent polyspermy Signup and view all the answers

What is the final destination of the primordial germ cells (PGCs) in spermatogenesis?

Left and right genital ridges Signup and view all the answers

What is the process of maturation of the spermatids to become structurally and functionally specialized?

Spermeiogenesis Signup and view all the answers

What is the structure that lines the seminiferous tubules?

Sertoli cells Signup and view all the answers

What is the primary function of the fast block to polyspermy?

To change the membrane potential of the oocyte Signup and view all the answers

What is the primary role of IP3 in the oocyte?

To release calcium ions from storage Signup and view all the answers

What is the result of the cortical reaction in the oocyte?

Release of proteases, peroxidases, and mucopolysaccharides Signup and view all the answers

What is the purpose of the second block to polyspermy?

To harden the zona pellucida and vitelline membrane Signup and view all the answers

What is the consequence of calcium ion activation of NAD+ kinase?

Phosphorylation of NAD to NADP+ Signup and view all the answers

What is the significance of lipid synthesis during oocyte activation?

Preparation for the synthesis of plasma membranes in newly formed cells Signup and view all the answers

What is the result of the fusion of the male and female pronuclei?

Formation of the zygote nucleus Signup and view all the answers

What is the role of phospholipase C in the regulation of sperm entry into the oocyte?

To activate the cortical reaction Signup and view all the answers

What is the role of DAG in regulating cellular responses during oocyte activation?

Phosphorylation of target proteins Signup and view all the answers

What is the significance of the fast block to polyspermy?

It is an early metabolic response to polyspermy Signup and view all the answers

What is the function of cyclins and cyclin-dependent kinases in the oocyte?

Regulation of cell cycle progression Signup and view all the answers

What is the result of the depolarization of the plasma membrane?

Change in membrane potential from -70 to +10 millivolts Signup and view all the answers

What is the site of fertilization in mammals?

Ampulla of the fallopian tube Signup and view all the answers

What is the role of the sperm in the regulation of sperm entry into the oocyte?

To bind to receptors on the plasma membrane of the oocyte Signup and view all the answers

What is the function of the fimbriae in the female reproductive tract?

Capture and transport of the oocyte Signup and view all the answers

What is the pH of the natural vaginal acidity?

pH 3.5 Signup and view all the answers

What is the result of the fertilization process?

Formation of the zygote nucleus Signup and view all the answers

What is the site of deposition of sperm in common mammals?

Upper vaginal canal Signup and view all the answers

What is the significance of the second block to polyspermy?

It is a slow chemical response to polyspermy Signup and view all the answers

What is the consequence of hyperactivated motility of sperm in the fallopian tube?

Penetration of the oocyte Signup and view all the answers

What is the primary function of the chemoattractant released by the jelly coat of the oocyte?

To ensure species-specific attraction between sex cells Signup and view all the answers

What is the primary function of proteases in the fertilization process?

To break down molecular bonds between the vitelline envelope and the plasma membrane Signup and view all the answers

In which type of fertilization does the deposition of sperm cells into the female reproductive tract occur?

Internal fertilization Signup and view all the answers

What is the term for the prevention of more than one sperm entering the oocyte?

Regulation of sperm entry Signup and view all the answers

What is the result of the cortical reaction in the fertilization process?

The release of chemical substances forming the fertilization membrane Signup and view all the answers

What is the purpose of mucopolysaccharides in the fertilization process?

To produce osmotic gradients, causing water to rush between the vitelline envelope and the plasma membrane Signup and view all the answers

Which process involves the formation of a fibular protein to further penetrate the vitelline layer?

Acrosomal reaction Signup and view all the answers

What is the role of peroxidases in the fertilization process?

To harden the fertilization membrane by cross-linking tyrosine residues of adjacent proteins Signup and view all the answers

What is the term for the fusion of the genetic materials of the sperm and the oocyte?

Pronuclear fusion Signup and view all the answers

Which type of fertilization is characteristic of aquatic vertebrates such as fish and amphibians?

External fertilization Signup and view all the answers

What is the term for the actual fusion of the sex cells' plasma membranes?

Fertilization cone Signup and view all the answers

What is the term for the release of eggs into the aquatic environment?

Spawning Signup and view all the answers

What is the space between the plasma membrane of the oocyte and the vitelline layer?

Perivitelline space Signup and view all the answers

What is the outer layer of the egg cell that is penetrated by the acrosomal process?

Vitelline layer Signup and view all the answers

What is the result of the mucopolysaccharides producing osmotic gradients?

The separation of the vitelline envelope and the plasma membrane Signup and view all the answers

What is the term for the activation of the oocyte metabolism to start development?

Late responses Signup and view all the answers

What is the purpose of the fertilization membrane?

To prevent other sperm from attaching to the oocyte membrane Signup and view all the answers

Which scientists are credited with the first observation of fertilization using sea urchins as model organisms?

Oscar and Richard Hertwig Signup and view all the answers

What happens to the pH of semen during insemination?

It reverts back to pH of 7.2 Signup and view all the answers

What is the consistency of cervical mucus during ovulation?

Watery and thin Signup and view all the answers

What is the final destination of the sperm for fertilization?

The ampulla of the fallopian tube Signup and view all the answers

What is the purpose of capacitation in sperm?

To prepare the sperm for fertilization Signup and view all the answers

How long does capacitation typically take in humans?

5-8 hours Signup and view all the answers

What is the role of hyaluronidase in fertilization?

It breaks down the corona radiata Signup and view all the answers

What determines the sex of the embryo in mammals?

The presence of X or Y chromosomes in the sperm Signup and view all the answers

What is the result of fertilization of an oocyte by a sperm with an X chromosome?

A female embryo with XX chromosomes Signup and view all the answers

What is the significance of the completion of the second meiotic block in fertilization?

It restores the diploid number of chromosomes Signup and view all the answers

What is the role of calcium ions in fertilization in amphibians?

They release the metaphase II arrest Signup and view all the answers

Study Notes

Oogenesis in Aves

The ovary contains multiple oocytes at various stages of development.
The ovary is divided into regions: infundibular, magnum, shell, and shell gland.
Fertilization must occur before the addition of accessory coverings.
VitaLink PH: hen layers are injected with hormones to hasten ovulation, allowing two oocytes to be released simultaneously.

Oogenesis in Amphibians

The ovary contains oocytes at various stages of development.
Characteristic of amphibian oocytes:
- Mitosis is continuous.
- Egg maturation requires 3 years, starting after metamorphosis.
- 3-year cycle of oogenesis.
Phases of oocyte maturation:
- Previtellogenic phase: before yolk deposition.
- Vitellogenic phase: yolk accumulation.
- Formation of lampbrush chromosomes and nucleoli.
Oocytes are actively transcribing genes.
Gene products are involved in cell metabolism, oocyte-specific processes, and early development.

Spermatogenesis

Starting point: primordial germ cells (PGCs) become specialized sex cells (spermatozoa).
Process involves:
- Mitotic multiplication.
- Meiosis (I and II).
- Differentiation stage: spermeiogenesis.
Mitosis in males occurs throughout life.
PGCs develop into spermatogonia, which undergo meiosis and spermeiogenesis.
Spermeiogenesis is an important step in spermatogenesis, where spermatids mature into structurally and functionally specialized spermatozoa.
The process takes approximately 24 days.

Categories of Changes during Spermatogenesis

Reorganization of cytoplasm:
- Golgi Apparatus forms an acrosome cap.
- Centrioles aggregate.
- Mitochondria locate in the neck.
Progressive reduction in nuclear size and compaction of the nucleus.
Elimination of RNA, leaving only DNA.

Fertilization

The union of sex cells, which begins the formation of a new organism.
Two types of fertilization among vertebrates:
1. External fertilization (ex vivo): characteristic of aquatic vertebrates.
2. Internal fertilization (in vivo): characteristic of avians and mammals.
Major events in fertilization:
1. Contact and recognition between sperm and oocyte.
2. Regulation of sperm entry into the oocyte.
3. Fusion of genetic materials.
4. Activation of oocyte metabolism.

Fertilization Process: Sea Urchin Fertilization

Most of what is known about fertilization process is based on sea urchin fertilization.
Hertwig brothers observed fertilization using sea urchins as model organisms.
Image shows a schematic drawing of an aquatic animal's oocyte.
Outer to the plasma membrane of the egg cell is the vitelline envelope and jelly coat.
Jelly coat secretes a chemoattractant for species-specific recognition of sex cells.
Contact and recognition between sperm and oocyte:
1. Acrosomal reaction.
2. Formation of the fertilization cone.
3. Fusion of plasma membranes.
4. Cortical reaction.

Regulation of Sperm Entry into the Oocyte

First block to polyspermy: electrical in nature.
Second block to polyspermy: chemical in nature.
Involves calcium release and cortical reaction.
Peroxidases harden the fertilization membrane.

Fusion of Genetic Materials

Union of gametes.
Male pronucleus and female pronucleus meet, forming the zygote nucleus.

Metabolic Activation of the Oocyte (in Sea Urchin)

Cortical reaction (cortical granule exocytosis) is an early response of the cell.
Phospholipase C activation.
IP3 causes the release of calcium ions.
Calcium ions activate calcium-dependent kinases.
NAD is phosphorylated to NADP+.
NADP+ serves as a coenzyme involved in lipid synthesis.
DAG stimulates protein kinase C.
Protein kinase C phosphorylates target proteins, activating DNA replication and cytoplasmic movements of morphogenetic material.### Metabolic Responses of the Oocyte
Diacylglycerol (DAG) activates protein kinase C, phosphorylating target proteins, resulting in cellular responses such as protein synthesis for DNA replication and cell cycle regulation.
DAG is associated with chromosomes, involving proteins like histones.
Fertilization triggers rapid DNA replication, synthesis of DNA blocks, and synthesis of chromosomal proteins (like histones) and proteins for cell cycle regulation (like cyclins and cyclin-dependent kinases).

Transport of Gametes and Fertilization in Mammals

The female reproductive tract is associated with the ovary, with the fallopian tube's ostium (opening) surrounded by fimbriae (finger-like structures).
During ovulation, the oocyte is released and captured by the fimbriae, then travels down to the uterus, taking 4-5 days to reach the uterus.
Ampulla is the site of fertilization in the fallopian tube.

Sperm Transport in the Female Reproductive Tract

Insemination occurs in the upper vaginal canal (common mammals) or uterus (rodents).
Sperm travels through the cervix, utero-tubal junction, and ampulla of the fallopian tube, where hyperactivated motility of sperm occurs to penetrate the oocyte.

Sperm Barriers

Natural vaginal acidity (pH 3.5) is a barrier, but semen's buffering capacity helps revert it to pH 7.2.
Thick cervical mucus is a barrier, but it becomes more watery during ovulation, facilitating sperm swimming.
Wide uterus and utero-tubal junction are also barriers.

Sperm Capacitation

Sperm undergo capacitation, a period of conditioning, in the male reproductive tract.
Capacitation involves removal of glycoprotein protein coat and other semenar proteins that cover the acrosome cap.
The length of capacitation varies from species to species (e.g., 1 hour in mice, 6 hours in rabbits, 5-8 hours in humans).

Transport of the Fertilized Oocyte

The fertilized oocyte forms the zygote, undergoing cleavage, and reaches the 4-cell stage by Day 3-4 and the 8-cell stage by Day 8.
Around Day 6-7, it is implanted in the uterus as a blastocyst.

Union of Gametes in Mammals

The acrosome cap releases hyaluronidase, which digests the corona radiate, allowing the sperm to penetrate the zona pellucida.
The sperm specific receptor is present in the zona pellucida.
Hydrolytic enzymes like acrosin help in digesting the zona pellucida.

X and Y Sperms: Sex Determination

X-chromosome sperm and Y-chromosome sperm (female and male sperms, respectively) determine the sex of the embryo.
23 X + 23 X results in a female embryo, while 23 Y + 23 X results in a male embryo.

Accomplishments of Fertilization

Completion of the second meiotic block, metaphase II arrest, is lifted off.
Normal diploid number of chromosomes (23 + 23 = 46) is restored.
Sex of the future embryo is determined.
Genetic variation occurs.
Metabolic activation of the egg is triggered.

Fertilization in Amphibians

Progesterone hormone lifts off diplotene block in frogs.
Oocytes are arrested at metaphase II.
At fertilization, metaphase II arrest is lifted, and calcium ions are released, activating Calmodulin-Dependent Protein Kinase II (Cam-PKII).
Cam-PKII degrades cytostatic factors (CSF), allowing meiosis II to complete.
Fertilization is completed, and polar bodies are released.

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Learn about the structure and composition of ovarian follicle and ovum, including the roles of different layers and regions.