Lecture 7: Female developmental reproduction
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Questions and Answers

What is the primary function of the Zona Pellucida during fertilization?

  • It stores nutrients necessary for oocyte development.
  • It acts as a barrier against bacterial infection.
  • It protects the oocyte from environmental damage.
  • It facilitates sperm binding and prevents polyspermy. (correct)

Which process directly leads to the extrusion of the polar body during meiosis?

  • The formation of the germinal vesicle.
  • Symmetric division of the oocyte.
  • Asymmetric division of the oocyte. (correct)
  • The surge of Follicle Stimulating Hormone (FSH).

What triggers the oocyte to resume meiosis just before ovulation?

  • Follicle Stimulating Hormone (FSH) increase.
  • Gradual decrease in progesterone levels.
  • Estrogen levels dropping.
  • A surge of Luteinizing Hormone (LH). (correct)

At which stage is the oocyte considered a Metaphase II (MII) oocyte?

<p>When it is released from the ovary during ovulation. (C)</p> Signup and view all the answers

What happens to the germinal vesicle during meiotic maturation?

<p>It breaks down, allowing meiosis to resume. (B)</p> Signup and view all the answers

Which protein is specifically involved in meiotic recombination?

<p>SCP-1 (C)</p> Signup and view all the answers

What is the primary role of FoxL2 in follicle assembly?

<p>Involved in granulosa cell differentiation (A)</p> Signup and view all the answers

What consequence may result from the absence of key proteins involved in primordial follicle formation?

<p>Potential for subfertility or sterility (C)</p> Signup and view all the answers

At what developmental stage are oocytes arrested during follicle assembly?

<p>Prophase I of meiosis (C)</p> Signup and view all the answers

When is follicle assembly typically completed in mice?

<p>Postnatal day 5 (D)</p> Signup and view all the answers

What is the primary function of the ovaries related to hormones?

<p>Production of hormones for pregnancy and secondary sex characteristics (D)</p> Signup and view all the answers

What does the ovarian reserve consist of?

<p>The primordial follicles available for future ovulation at birth (A)</p> Signup and view all the answers

Which protein is necessary for the development of oocytes?

<p>Nobox (D)</p> Signup and view all the answers

During which phase do primordial germ cells become known as oogonia?

<p>Upon arrival at the developing gonad (D)</p> Signup and view all the answers

What occurs to oogonia after they stop dividing by mitosis?

<p>They enter the first stage of meiosis (C)</p> Signup and view all the answers

Which protein is involved in cell signaling and regulation within the context of follicle assembly?

<p>Notch (A)</p> Signup and view all the answers

What marks the formation of a primordial follicle?

<p>Granulosa cells encasing the oocyte (A)</p> Signup and view all the answers

Which statement accurately describes the germ cell nests?

<p>They consist of interconnected oogonia supported by somatic cells. (C)</p> Signup and view all the answers

What is the initial developmental stage of female gametes in the ovary called?

<p>Oogonia (A)</p> Signup and view all the answers

What is a significant limitation once the primordial follicles have formed?

<p>The number of available oocytes decreases over time (C)</p> Signup and view all the answers

What is the significance of somatic cells surrounding the oocytes?

<p>They develop into granulosa cells vital for the oocyte's development. (B)</p> Signup and view all the answers

Which process marks the beginning of oogenesis in the developing ovary?

<p>Entry into the first stage of meiosis (A)</p> Signup and view all the answers

Which marker is NOT expressed by PGCs upon arriving at the gonad?

<p>Alkaline Phosphatase (A)</p> Signup and view all the answers

What process leads to the formation of germ cell nests in females?

<p>Incomplete cytokinesis during proliferation (C)</p> Signup and view all the answers

At what embryonic day do female germ cells begin meiosis in mice?

<p>Day 13.5 (A)</p> Signup and view all the answers

Which signal is NOT mentioned as influencing female germ cell development?

<p>Sertoli cell signals (A)</p> Signup and view all the answers

Which cells continue to proliferate, forming multiple layers around the oocyte in the secondary follicle?

<p>Granulosa cells (C)</p> Signup and view all the answers

What transformation occurs in XY gonocytes around 12.5 days post-conception?

<p>They enter a resting phase (A)</p> Signup and view all the answers

What is the role of transzonal projections between granulosa cells and the oocyte?

<p>They facilitate communication and nutrient exchange. (C)</p> Signup and view all the answers

Which of the following is primarily responsible for directing female germ cell differentiation?

<p>Signals from surrounding somatic cells (A)</p> Signup and view all the answers

What is the primary role of Stra8 in female germ cell development?

<p>Induce the beginning of meiosis (A)</p> Signup and view all the answers

Which statement correctly describes the role of theca cells in follicle development?

<p>They develop from surrounding stromal cells to encase the growing follicle. (D)</p> Signup and view all the answers

At what stage is the oocyte when it is meiotically arrested?

<p>At the primary oocyte stage (B)</p> Signup and view all the answers

How do male germ cells transition from gonocytes?

<p>By entering a phase of quiescence (D)</p> Signup and view all the answers

What happens to the granulosa cells as the follicle develops into the secondary stage?

<p>They increase in number, forming multiple layers. (A)</p> Signup and view all the answers

What key characteristic defines PGCs upon their arrival at the gonad?

<p>Large, round cells with a large nucleus (B)</p> Signup and view all the answers

What defines the secondary follicle in terms of oocyte development?

<p>The oocyte continues to grow in size and secretes zona pellucida. (B)</p> Signup and view all the answers

Why is the proliferation of granulosa cells critical for the growing oocyte?

<p>They provide hormonal signals necessary for oocyte maturation. (B)</p> Signup and view all the answers

What is the purpose of the zona pellucida during the fertilization process?

<p>To prevent the fertilization of multiple sperm. (A)</p> Signup and view all the answers

Flashcards

Oogenesis

The process by which female gametes (eggs) are formed in the ovaries.

Primordial Germ Cells (PGCs)

The precursor cells that will eventually give rise to oocytes (eggs) in females.

PGC Migration

The movement of primordial germ cells from their site of origin to the developing gonad (ovary or testes).

Oogonia

The cells in the developing ovary that are the direct precursors to oocytes (eggs).

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Germ Cell Nests

Groups of interconnected oogonia in the developing ovary, surrounded by somatic cells.

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Somatic Cells

Non-reproductive cells that support the development of germ cells in the ovary.

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Somatic Cell Invasion

The stage where individual oocytes become surrounded by somatic cells, which will later form granulosa cells.

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PGC Morphological Change

The process by which PGCs become large, round cells with a large, round nucleus.

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GCNA (Germ Cell Nuclear Antigen)

A specific marker expressed by PGCs upon arrival at the gonad, indicating germ cell identity.

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SSEA (Stage-Specific Embryonic Antigen)

A marker expressed by PGCs upon arrival at the gonad. PGCs express different developmental markers. 

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Thy1

A cell surface marker expressed by PGCs upon arrival at the gonad. This marker helps track PGC development.

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C-kit

A receptor protein expressed by PGCs upon arrival at the gonad. It helps with cell signaling and differentiation.

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Alkaline Phosphatase

An enzyme expressed by PGCs before embryonic day 14.5 but not afterwards.

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Sex Determination

The process by which somatic cells in the gonad influence the differentiation of germ cells into oocytes or spermatocytes.

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Meiosis in Female Germ Cells

The entry of female germ cells into meiosis, triggered by signals like retinoic acid and Stra8.

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Retinoic Acid

A key signal that stimulates the start of meiosis in female germ cells.

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Key proteins in follicle formation

Proteins essential for the breakdown of germ cell clusters and the formation of primordial follicles, influencing fertility.

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What does SCP-1 do?

A protein critical for recombination events during meiosis, ensuring accurate chromosome pairing.

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What does FoxL2 do?

A protein playing a role in the development of granulosa cells, the cells surrounding the egg.

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What does Nobox do?

An essential protein for the growth and development of the oocyte, the future egg cell.

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What does Notch do in follicle formation?

A protein involved in cell communication and regulation, contributing to the overall process of follicle development.

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What happens when key follicle proteins are missing?

Lack of key follicle formation proteins can lead to incomplete breakdown of germ cell nests, faulty primordial follicle formation, and potentially infertility.

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What is follicle assembly?

The process where granulosa cells surround a developing oocyte (arrested in Prophase I of meiosis) to create a primordial follicle.

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Define ovarian reserve.

The finite number of primordial follicles present in the ovary at birth (or shortly after in mice), representing the entire supply of eggs a female will have throughout her life.

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Why is follicle assembly important?

The follicles formed during follicle assembly represent the complete supply of oocytes a woman will have throughout her reproductive life. No new primordial follicles can be generated after this stage.

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When is follicle assembly completed?

The time period when follicle assembly is typically completed in mice (day 5 after birth) and in humans (around birth).

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Zona Pellucida

The layer surrounding the oocyte that plays a crucial role in fertilization by preventing polyspermy and facilitating sperm binding.

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Granulosa Cell Proliferation

Granulosa cells continue to proliferate and form multiple layers around the growing oocyte in the secondary follicle.

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Transzonal Projections

Extensions from granulosa cells that pass through the zona pellucida to make contact with the oocyte's surface.

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Theca Cells

These cells surround the developing follicle and contribute to its growth and function.

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Oocyte Growth in Secondary Follicle

The continued growth of the oocyte in the secondary follicle, accompanied by increased complexity and maturation.

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Polyspermy

The process of fertilization by multiple sperm, which is prevented by the zona pellucida.

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Oocyte Maturation

The process of the oocyte becoming mature and ready for fertilization.

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Germinal Vesicle (GV) Stage

The stage where the oocyte is arrested in its development, characterized by the presence of the germinal vesicle, the nucleus of the oocyte.

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Luteinizing Hormone (LH) Surge

This surge in LH triggers the oocyte to resume meiosis, leading to meiotic maturation and ovulation.

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Cumulus Cells Expansion

The cumulus cells surrounding the oocyte expand and transform into a cloud-like structure, which is crucial for ovulation.

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Polar Body Formation

The oocyte undergoing asymmetrical division during meiosis, extrudes half of its nuclear material into a small structure known as the polar body, leaving the oocyte with only half of its original chromosome count.

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Study Notes

Female Developmental Reproduction

  • The ovary has three main functions:
    • Making hormones, impacting pregnancy and secondary sexual characteristics
    • Storing female germline, protecting it from chemical and physical insults, and maintaining quiescence
    • Generating mature oocytes, crucial for fertility and species perpetuation

Oogenesis

  • Process of forming female gametes (oocytes) within the ovaries
  • A lengthy process, beginning in fetal development and concluding decades later in adulthood
  • Takes considerable time to produce an oocyte

Part 1: Development of Oocytes in the Embryonic Ovary

  • Development from primordial germ cells (PGCs) to primordial follicles

    • PGC specification occurs early in embryonic development, specifying precursor cells for oocytes (in females) or sperm (in males)
    • PGCs undergo mitosis and migrate to increase their numbers, eventually reaching the developing gonads (ovaries).
    • Once in the gonad, they are called gonocytes and then oogonia.
    • Oogonia multiply and form germ cell nests.
    • Somatic cells surround these nests, supporting germ cell development.
    • Oogonia then enter meiosis, becoming oocytes.
    • Somatic cells envelop oocytes, forming primordial follicles.

  • Arrest during meiosis: oocytes arrest in the diplotene stage of the first meiotic prophase.

  • Formation of primordial follicles: a single layer of granulosa cells surrounds the oocyte.

Timeline of Germ Cell Development in Mice

  • Development from embryonic day 6 to postnatal day 5

Comparison Between Mice and Humans

  • Synchronization: Mice have synchronized oogenesis, while human oogenesis is not synchronized. This means stages of germ cell development overlap.

  • Follicle Timing: Follicle formation is completed postnatally in mice, while it happens before birth in humans.

Oogenesis Stages: Mice vs. Humans

  • Timing - In mice, it is synchronous, while in humans, it is asynchronous.

Timing of Follicle Formation

  • In mice – completed shortly after birth
  • In humans – completed during fetal development

Formation of Primordial Germ Cells: Origin and Initial Population

  • Primordial germ cells originate in the proximal epiblast, an early embryonic layer.
  • Start with about 6 cells around embryonic day 6.25 in mice, growing to approximately 40 cells by day 7.25.

Characteristics of Newly Specified PGCs

  • Smooth morphology when stationary
  • Transcriptionally active - expressing genes required for function and identity.
  • Suppressing somatic lineage genes via Blimp1.

PGC Migration

  • Migration begins around embryonic day 7.5 in mice.

  • PGCs migrate from the primitive streak to the yolk sac, then through the endoderm hindgut, eventually reaching the genital ridge/gonadal ridge around embryonic day 10.5

  • Signalling pathways: important factors for migration include SDF-1 and CXCR4 and changes in cytoskeleton.

Changes Upon Arrival

  • Loss of polarity in morphology
  • Cessation of migratory behavior.

Morphological Change

  • Transition to large, round cells with a large, round nucleus, expressing specific markers such as GCNA and Thy1.

Loss of Alkaline Phosphatase

Prophase I of Meiosis

  • Divided into five steps: Leptotene, Zygotene, Pachytene, Diplotene, and Diakinesis.

Arrested Development

  • In males, spermatogonia continue meiosis toward sperm cells.
  • In females, primary oocytes arrest in diplotene.

Importance of Meiotic Recombination

  • Generates genetic diversity.

Nest Formation

  • Oogonia undergo incomplete cytokinesis, remaining clustered in nests.
  • Crucial for nutrient and material transfer to support growth.

Nest Breakdown

  • Breakdown occurs around birth in mice or mid-gestation in humans.
  • Involvement of pre-granulosa cells, formation of individual primordial follicles.

Follicle Assembly

  • Granulosa cells surrounding oocytes, forming primordial follicles.

Ovarian Reserve

  • Primordial follicles represent the entirety of oocytes available for fertilization throughout a female's lifetime.

Loss of Proliferative Ability

  • Once oocytes enter meiosis, they lose their ability to divide or increase in number.

Part 2: Development of Oocytes in the Postnatal Ovary

Primary Follicle

  • Characterized by a growing oocyte and columnar granulosa cells proliferating.

Secondary Follicle

  • Oocyte growth continues.
  • Zona pellucida forms.
  • Granulosa cells proliferate, forming multiple layers around the oocyte.

Tertiary/Antral Follicle

  • Formation of the antrum (fluid-filled cavity).
  • Granulosa cells differentiate into mural and cumulus cells.

Graafian Follicle

  • FSH and LH stimulate further growth, estradiol production.

Cyclic FSH Release

Cumulus Oocyte Complex and Germinal Vesicle Stage

  • Oocyte preparation for final stages of meiosis

Meiotic Maturation

  • Completion of meiosis I and II, polar bodies, one mature ovum.
  • LH surge triggers meiotic resumption.

Ovulation

  • Release of the cumulus-oocyte complex.
  • Formation of corpus luteum from remnants of the follicle (crucial for maintaining uterine lining and supporting pregnancy).

Time Course of Follicle Development

  • Specific timeframes for each stage are diverse, varying by species.

Consequences of Absence

  • Inability of primordial follicles to form, impacting fertility.

First Natural Ovulation

  • gentle versus explosive release.

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Explore the crucial aspects of female reproductive development, including hormone production, oocyte formation, and the stages of oogenesis. This quiz covers the development of oocytes from embryonic stages through to maturity, highlighting key concepts in female fertility.

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