Lecture 7: Female developmental reproduction

Podcast

Play an AI-generated podcast conversation about this lesson

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?

When it is released from the ovary during ovulation. Signup and view all the answers

What happens to the germinal vesicle during meiotic maturation?

It breaks down, allowing meiosis to resume. Signup and view all the answers

Which protein is specifically involved in meiotic recombination?

SCP-1 Signup and view all the answers

What is the primary role of FoxL2 in follicle assembly?

Involved in granulosa cell differentiation Signup and view all the answers

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

Potential for subfertility or sterility Signup and view all the answers

At what developmental stage are oocytes arrested during follicle assembly?

Prophase I of meiosis Signup and view all the answers

When is follicle assembly typically completed in mice?

Postnatal day 5 Signup and view all the answers

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

Production of hormones for pregnancy and secondary sex characteristics Signup and view all the answers

What does the ovarian reserve consist of?

The primordial follicles available for future ovulation at birth Signup and view all the answers

Which protein is necessary for the development of oocytes?

Nobox Signup and view all the answers

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

Upon arrival at the developing gonad Signup and view all the answers

What occurs to oogonia after they stop dividing by mitosis?

They enter the first stage of meiosis Signup and view all the answers

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

Notch Signup and view all the answers

What marks the formation of a primordial follicle?

Granulosa cells encasing the oocyte Signup and view all the answers

Which statement accurately describes the germ cell nests?

They consist of interconnected oogonia supported by somatic cells. Signup and view all the answers

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

Oogonia Signup and view all the answers

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

The number of available oocytes decreases over time Signup and view all the answers

What is the significance of somatic cells surrounding the oocytes?

They develop into granulosa cells vital for the oocyte's development. Signup and view all the answers

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

Entry into the first stage of meiosis Signup and view all the answers

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

Alkaline Phosphatase Signup and view all the answers

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

Incomplete cytokinesis during proliferation Signup and view all the answers

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

Day 13.5 Signup and view all the answers

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

Sertoli cell signals Signup and view all the answers

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

Granulosa cells Signup and view all the answers

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

They enter a resting phase Signup and view all the answers

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

They facilitate communication and nutrient exchange. Signup and view all the answers

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

Signals from surrounding somatic cells Signup and view all the answers

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

Induce the beginning of meiosis Signup and view all the answers

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

They develop from surrounding stromal cells to encase the growing follicle. Signup and view all the answers

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

At the primary oocyte stage Signup and view all the answers

How do male germ cells transition from gonocytes?

By entering a phase of quiescence Signup and view all the answers

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

They increase in number, forming multiple layers. Signup and view all the answers

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

Large, round cells with a large nucleus Signup and view all the answers

What defines the secondary follicle in terms of oocyte development?

The oocyte continues to grow in size and secretes zona pellucida. Signup and view all the answers

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

They provide hormonal signals necessary for oocyte maturation. Signup and view all the answers

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

To prevent the fertilization of multiple sperm. Signup and view all the answers

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.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

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.