Female Developmental Reproduction PDF

🥽 Lecture 7: Female developmental reproduction Context The ovary has three main functions: Make hormones → pregnancy, secondary sex characteristics Store female germline → protection chemicals/phy...

🥽 Lecture 7: Female developmental reproduction Context The ovary has three main functions: Make hormones → pregnancy, secondary sex characteristics Store female germline → protection chemicals/physical insults, maintenance of quiescence Generate mature oocytes → fertility, perpetuation of the species Oogenesis The process by which female gametes are formed in the ovaries Takes a lot of time to generate an oocyte Begins in fetal development, concludes decades later in the mature adult Part 1 - Development of oocytes in the embryonic ovary Lecture 7: Female developmental reproduction 1  Development from primordial germ cell (PGC) → primordial follicle 1. PGC specification: specified early in embryonic development - these are the precursor cells that will eventually give rise to oocytes in females (or sperm in males). 2. After specification - PGC undergoes mitosis & migration to increase their number while migrating from their site of origin to the developing gonad (which becomes the ovary in females). 3. Once PGCs arrive at the gonad, they are referred to as gonocytes and later as oogonia (the term used for these cells in the developing ovary). 4. In the developing ovary, oogonia continue to proliferate, forming germ cell nests → nests consist of interconnected oogonia, meaning many germ cells remain connected to each other. a. These nests are surrounded by somatic cells, which are non- reproductive cells that support the development of germ cells. 5. At a certain point, oogonia stop dividing by mitosis and enter the first stage of meiosis - this entry into meiosis marks the beginning of their transformation into oocytes. 6. Somatic cell invasion - As the germ cell nests begin to break down, individual oocytes become surrounded by somatic cells (which will later form granulosa cells) 7. Meiotic arrest - at this stage, the oocytes arrest in the diplotene stage of the first meiotic prophase, meaning they pause in the middle of this Lecture 7: Female developmental reproduction 2  first stage of meiosis. 8. Formation of primordial follicle - earliest form of ovarian follicles, each primordial follicle consists of a single oocyte (arrested in meiosis) surrounded by a single layer of granulosa cells. a. The granulosa cells provide structural support and signals to the oocyte Timeline of Germ Cell Development in Mice Embryonic Day 6 (E6) to Postnatal Day 5: Start: Germ cell development begins at embryonic day 6 (E6) with the specification of primordial germ cells (PGCs). End: It concludes postnatally by day 5 with the formation of primordial follicles, which are the earliest stages of follicle development in the ovary. Peak Germ Cell Number: Interestingly, the number of germ cells (oogonia or oocytes) in mammalian females peaks during Lecture 7: Female developmental reproduction 3  embryonic development. This means that a female has the highest number of germ cells during fetal life. Mitosis → Meiosis transition Loss of Proliferation Ability: During the transition from mitosis (cell division to increase cell number) to meiosis (cell division to produce eggs with half the genetic material), oocytes lose the ability to proliferate. Once they enter meiosis, they no longer divide. Comparison Between Mice and Humans Synchronisation of Oogenesis Stages In Mice: The stages of oogenesis are synchronous, meaning that all the processes involved in the development of oocytes, such as the transition from mitosis to meiosis occur simultaneously → ensures that the majority of germ cells follow the same timeline, entering each stage of development together. In Humans: The stages of oogenesis are not synchronised. Instead, mitotic germ cells and meiotic germ cells can coexist with newly formed follicles. This means that in humans, different stages of germ cell development can overlap, with some cells still dividing while others are already maturing into oocytes within follicles. Timing of Follicle Formation In Mice: Follicle formation, which is the process by which oocytes become enclosed in a group of supporting cells called granulosa cells, is completed just after birth. This means that in mice, the development of primordial follicles (the earliest stage of follicle development) continues postnatally. In Humans: Follicle formation is completed before birth, during fetal development. This means that by the time a human baby girl is born, the process of forming primordial follicles is already finished. Specification of germ cells(mouse) Pluripotent Cells: Early in development, cells that have the potential to become various cell types (pluripotent cells) are induced to form the germ cell lineage, which will give rise to PGCs. Timing of Primordial Germ Cell Formation Lecture 7: Female developmental reproduction 4  In Mice: The formation of primordial germ cells occurs between embryonic day 5.5 and embryonic day 7.5. In Humans: This process occurs around week 2 to 3 of gestation, indicating that it happens very early in development in both species. Origin and Initial Population The initial population of primordial germ cells starts with about 6 cells at embryonic day 6.25 in mice. By embryonic day 7.25, this number increases to approximately 40 specified cells. These cells originate from the proximal epiblast, which is an early layer of cells in the developing embryo. Location and Identification Primordial germ cells are first observed as a cluster of alkaline phosphatase-positive cells in the extra-embryonic mesoderm around embryonic day 7.25. Alkaline phosphatase positivity is used as a marker to identify these cells, indicating that these PGCs develop outside the embryo, in the extra-embryonic mesoderm. Signaling Pathways Involved Formation of PGCs is induced by paracrine signals (signals that act locally near the site of their release) from adjacent tissues, particularly the extra-embryonic ectoderm and visceral endoderm. Key signals include BMP2, BMP4, and BMP8, which activate SMAD 1/5/8 proteins. This signaling cascade leads to the expression of specific genes like fragilis, blimp1, and stellar in the primordial germ cells, which are essential for their specification and development. Lecture 7: Female developmental reproduction 5  Characteristics of newly specified PGCs Smooth round morphology when stationary Transcriptionally active - actively expressing genes necessary for their function and identity A crucial part of this is the suppression of somatic lineage genes, which is controlled by the transcription factor Blimp1 → this ensures that PGCs do not differentiate into somatic cells and remain committed to the germ cell lineage. Express pluripotency markers (Oct3/4, Sox2, Nanog) Express unique PGC genes (Nanos3, Prdm14, Pmrt5, Ssea1, E-cadherin, Tnap) PGCs undergo epigenetic reprogramming, which involves significant changes to their DNA methylation and histone modification patterns PGCs are highly proliferative, meaning they rapidly divide to increase their number during early development. PGC Migration Lecture 7: Female developmental reproduction 6  Polarised Morphology: As PGCs prepare to migrate, they develop a polarized shape, which means they have a distinct front (leading edge) and back (lagging edge). The leading edge is involved in moving forward by extending protrusions and adhering to the surrounding tissue, while the lagging edge retracts to propel the cell forward. Migration Pathway: Migration starts around embryonic day 7.5. PGCs begin their journey from the primitive streak, a temporary structure in the early embryo, moving into the yolk sac. From there, they pass through the endoderm hindgut and finally reach the developing gonad/genital ridge/gonadal ridge around embryonic day 10.5. While migrating, PGCs continue to proliferate, increasing their numbers significantly: ~100 cells at E8.5 ~350 cells at E9.5 ~1000 cells at E10.5, when they arrive at the gonad Lecture 7: Female developmental reproduction 7  G2 Arrest and Chromatin Remodeling: Undergo a transient G2 arrest during migration while chromatin remodelled and parental imprints are erased How do PGCs know where to go? PGC’s follow directional cues from surrounding somatic cells to find their way to the gonads → signals include both attractive cues (which guide the cells toward their destination) and repulsive cues (which help avoid incorrect pathways) SDF-1 (Stromal-Derived Factor 1): Source: SDF-1 is a key attractive signal produced by the genital ridges (the developing gonads). These ridges are shown as green cell populations in the schematic. Function: SDF-1 acts as a chemoattractant, guiding the migrating PGCs toward the genital ridges where they need to arrive. CXCR4 Receptor: Expression: The receptor for SDF-1 is called CXCR4, a type of G protein-coupled receptor (GPCR). This receptor is expressed on the surface of migrating PGCs. Activation: When SDF-1 binds to CXCR4, it triggers a signaling cascade inside the PGCs. Signal Transduction: Cytoskeletal Changes: Activation of CXCR4 leads to changes in the cell's cytoskeleton, the structural network within the cell that determines its shape and movement. Lecture 7: Female developmental reproduction 8  Small GTPases: These are small signaling proteins that further regulate the cytoskeletal changes necessary for effective migration. Colonisation of the genital ridge Migration Path: Hindgut to Genital Ridge: Primordial germ cells migrate from the hindgut through the embryonic environment to reach the genital ridge, which will develop into the gonad (ovary or testis). Timing: This migration completes around embryonic day 10.5 in mice or weeks 4 to 5 in humans. Changes Upon Arrival: Loss of Polarity: Upon reaching the genital ridge, PGCs lose their polarized morphology (leading and lagging edges) and cease their migratory behavior. Lecture 7: Female developmental reproduction 9  Morphological Change: They become large, round cells with a similarly large, round nucleus. Expression Profile: Markers: Upon arriving at the gonad, PGCs express specific markers including: GCNA (Germ Cell Nuclear Antigen) SSEA (Stage-Specific Embryonic Antigen) Thy1 C-kit Loss of Alkaline Phosphatase: After embryonic day 14.5, PGCs stop expressing alkaline phosphatase, making this marker unsuitable for identifying them at this stage. Somatic cells in the gonad influence the differentiation of PGCs into either oocytes (in females) or spermatocytes (in males). This process, known as sex determination, is guided by various signals from surrounding somatic cells but is not detailed in this lecture series. Continue to proliferate and in females, germ cell nests are formed as a result of incomplete cytokinesis Image - green cells represent proliferating oogonia (female germ cells), and red cells represent the surrounding somatic cells. Lecture 7: Female developmental reproduction 10  Prophase I of meiosis Male Germ Cell Development: XY Gonocytes: In males, gonocytes (precursors to sperm cells) stop proliferating and enter a resting phase at around 12.5 days post-conception. They transition into spermatogonia, which are the stem cells that will later undergo meiosis to produce sperm. Female Germ Cell Development: Retinoic Acid and Stra8: In females, signals such as retinoic acid and the protein Stra8 induce the female germ cells (oogonia) to begin meiosis. This process starts around embryonic day 13.5 in mice or around week 13 in humans. Lecture 7: Female developmental reproduction 11  Transition to Primary Oocytes: As oogonia enter the first stage of meiosis, they complete DNA synthesis and transition directly from the G2 phase to Prophase I of meiosis. At this stage, they are referred to as primary oocytes. Prophase I of meiosis is divided into five steps: Leptotene: Chromosomes begin to condense and become visible. Zygotene: Homologous chromosomes start to pair up, forming synaptonemal complexes. Pachytene: Crossing over or recombination occurs, where homologous chromosomes exchange genetic material. Diplotene: The synaptonemal complex dissolves, and the homologous chromosomes begin to separate but remain attached at crossover points. Diakinesis: Chromosomes condense further, and the nuclear envelope breaks down, preparing for metaphase I. Arrested Development: In Males: Spermatogonia continue to divide and eventually undergo meiosis to form sperm. In Females: Primary oocytes are arrested in the diplotene stage of Prophase I and remain in this arrested state for a significant period, which can last from several weeks to decades until they are activated for ovulation later in life. Importance of Meiotic Recombination: Genetic Diversity: During the pachytene stage, meiotic recombination (crossing over) occurs. This process is crucial for generating genetic diversity within populations, as it shuffles genetic material between homologous chromosomes. Lecture 7: Female developmental reproduction 12  Nest formation and breakdown Nest Formation: Incomplete Cytokinesis: Oogonia (the precursors to oocytes) undergo rapid rounds of cell division but do not completely separate during cytokinesis. As a result, they remain attached, forming clusters or nests of interconnected oocytes. Purpose: Although the exact reason for incomplete cytokinesis is not fully understood, it is thought to facilitate the transfer of nutrients and organelles between oocytes, supporting their growth. Structure of Germ Cell Nests: Oocytes: Within these nests, the oocytes are arrested in the diplotene stage of Prophase I of meiosis. Surrounding Cells: The nests are surrounded by pre-granulosa cells (which will mature into granulosa cells) and stromal Lecture 7: Female developmental reproduction 13  mesenchyme, which provide support to the oocytes. Nest Breakdown: Timing: Nest breakdown occurs around birth in mice or during mid- gestation in humans. Process: This process involves the invasion of pre-granulosa cells into the nest. These cells migrate around each oocyte to form individual primordial follicles. Importance: The formation of primordial follicles from nests is crucial for establishing a reserve of oocytes, which is essential for female fertility. Oocyte Death: High Mortality: During nest breakdown, a significant proportion of oocytes (about two-thirds) undergo programmed cell death (apoptosis). This high rate of cell death is thought to be a normal part of the developmental process, though the reasons are not entirely clear. Possible Explanations: Altruistic Action: Some oocytes may donate essential cytoplasmic components to others before dying. Growth Factors: Oocytes that do not receive adequate growth factors or are not properly surrounded by granulosa cells may die. Defects: Oocytes with errors in meiotic recombination or other defects may be selectively eliminated. Proteins Involved: Key Proteins: Several proteins are essential for the proper breakdown of germ cell nests and the formation of primordial follicles: SCP-1: Involved in meiotic recombination. FoxL2: Plays a role in granulosa cell differentiation. Nobox: Necessary for oocyte development. Notch: Involved in cell signaling and regulation. Lecture 7: Female developmental reproduction 14  Consequences of Absence: Lack of these proteins can result in incomplete nest breakdown, improper formation of primordial follicles, and potential subfertility or sterility. Follicle assembly Follicle Assembly: refers to the process by which granulosa cells surround each oocyte (which is arrested in the diplotene stage of Prophase I of meiosis) to form primordial follicles. Follicle = oocytes + granulosa cells After the oocytes have been arrested in the diplotene stage, granulosa cells migrate from the surrounding area to encase the oocyte. This encapsulation marks the formation of a primordial follicle. Timing: In Mice: Follicle assembly is typically completed by around postnatal day 5. In Humans: Follicle assembly is generally completed by the time of birth. Ovarian Reserve: The primordial follicles present in the ovary at birth (or just after birth in mice) constitute the ovarian reserve. This reserve is the finite number of follicles available for future ovulation throughout the female's reproductive lifespan. Importance: Ovarian Reserve: The primordial follicles formed during this period represent the entire supply of oocytes a female will have throughout her life. After this point, no new primordial follicles can be generated. Lecture 7: Female developmental reproduction 15  Loss of Proliferative Ability: Once the primordial germ cells (oogonia) transition from mitosis to meiosis, they lose their ability to proliferate. This transition marks the point where oocytes become fixed in number and cannot increase in quantity. ^^ This underscores the importance of the early follicle assembly process for long-term reproductive health Part 2 - Development of oocytes in the postnatal ovary Primordial follicle → Primary follicle → Secondary follicle → Tertiary/Antral follicle → Graafin follicle → Ovulation Primordial Follicle Abundance and Distribution: Primordial follicles are the most abundant type in the ovary, distributed throughout the ovarian cortex. Structure: Lecture 7: Female developmental reproduction 16  Small, immature (primary) oocyte surrounded by single layer of squamous granulosa cells The oocyte has a central nucleus, often called a germinal vesicle The follicle is encased in a thin basal lamina outside the granulosa cells Developmental Arrest: The oocyte within the primordial follicle is arrested at the dictyotene stage of the first meiotic prophase, meaning these cells are non- dividing and in a state of quiescence or dormancy. Primordial follicles are established during embryogenesis in humans (or just after birth in some species like mice) and can remain dormant for many years until they are triggered to grow. Ovarian Reserve: These follicles represent the ovarian reserve, which is crucial for fertility. Once these follicles are depleted, infertility or age-related infertility occurs Activation and Folliculogenesis: Although most primordial follicles remain dormant, a small number are periodically activated to begin growth and development, leading to folliculogenesis (the maturation process of follicles). Longevity: Primordial follicles are long-lived structures. A follicle formed during embryogenesis in humans may remain dormant and only reach the ovulatory stage decades later. Lecture 7: Female developmental reproduction 17  Primary Follicle Activated primordial follicles develop into primary follicles Irreversibility: Once a follicle has been activated and starts growing, it is committed to either ovulate or undergo atresia (follicular death). It cannot revert to the primordial stage. 3 characteristics of follicle activation (1) Oocyte begins to grow (2) The granulosa cells change shape - become columnar Granulosa Cells: These cells surround the oocyte and play a crucial role in supporting its development. In the primordial follicle, granulosa cells are flat and squamous in shape. Shape Change: As the follicle is activated, the granulosa cells undergo a morphological transformation. They change from a flattened, squamous shape to a taller, columnar shape. This change in shape is significant because it reflects the granulosa cells' shift towards an active role in nourishing and supporting the growing oocyte. Lecture 7: Female developmental reproduction 18  (3) Granulosa cells proliferate Upon activation, these granulosa cells begin to divide rapidly, resulting in a significant increase in their number. This proliferation is important because it enhances the follicle’s ability to support the growing oocyte. Still meiotically arrested at this stage Secondary follicle Oocyte Growth and Secretion of Zona Pellucida: Oocyte Growth: oocyte (immature egg cell) continues to grow in size as it progresses to the secondary follicle stage. Zona Pellucida: The oocyte secretes a glycoprotein layer called the zona pellucida. This layer surrounds the oocyte and plays a vital role in fertilization by preventing polyspermy (fertilization by multiple sperm) and facilitating sperm binding. Proliferation of Granulosa Cells: Granulosa Cells: these cells continue to proliferate (divide and multiply), forming multiple layers around the oocyte. In the secondary follicle, the granulosa cells form a thicker, multi-layered structure around the growing oocyte. Lecture 7: Female developmental reproduction 19  Transzonal Projections: Even though the granulosa cells are separated from the oocyte by the zona pellucida, they remain in contact with the oocyte through structures called transzonal projections. These projections are extensions from the granulosa cells that pass through the zona pellucida and make contact with the oocyte's surface. This contact is crucial for the communication between the oocyte and the granulosa cells, allowing for the exchange of signals and nutrients that support the oocyte’s development. Formation of Theca Cells: Theca Cells: As the follicle develops into the secondary stage, the surrounding stromal cells (connective tissue cells in the ovary) organize around the follicle to form a layer called the theca. Theca Layers: The theca layer is divided into two parts: the theca interna (which produces hormones) and the theca externa (which provides structural support). Follicle Responsiveness to Gonadotropins (FSH and LH): Lecture 7: Female developmental reproduction 20  Gonadotropins: As the secondary follicle develops, it becomes responsive to two important hormones - Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH). These hormones are produced by the pituitary gland and play a critical role in the regulation of the menstrual cycle and folliculogenesis. FSH: Stimulates the growth of follicles and the proliferation of granulosa cells. LH: Works with FSH to stimulate the production of androgens by the theca cells, which are then converted to estrogen by granulosa cells. LH also plays a key role in triggering ovulation later in the cycle. Tertiary/Antral follicle Formation of the Antrum Antrum Development: formation of the antrum - a fluid-filled cavity that appears between the layers of granulosa cells. This cavity is essential for follicle growth and oocyte maturation. Structural Changes: The oocyte (egg cell) becomes acentric, meaning it shifts from the center of the follicle towards the edge Granulosa cells differentiate into mural and cumulus sub-types: Mural Granulosa Cells: These are the granulosa cells located on the outer edge of the follicle, playing a role in structural support and hormone production. Cumulus Cells: These cells remain closely associated with the oocyte, surrounding it and providing essential support for its development. The basal lamina is a thin, extracellular matrix layer that surrounds the follicle, providing structural support and separating the follicle from the surrounding ovarian tissue. The surrounding stromal cells differentiate into theca cells: Vascularised theca interna: This inner layer is closest to the follicle and is heavily vascularized (rich in blood vessels), Lecture 7: Female developmental reproduction 21  making it essential for hormone production, particularly androgens, which are precursors to estrogen. Vascularised theca externa: The outer layer provides additional structural support and contains connective tissue and blood vessels. FSH stimulates granulosa cells and LH stimulate theca cells to proliferate and differentiate Granulosa and theca cooperate to produce estradiol (a form of estrogen) Graafian follicle Lecture 7: Female developmental reproduction 22  Cyclic FSH Release: Follicle-Stimulating Hormone (FSH) is released cyclically from the pituitary gland, which promotes the survival and development of a group of antral follicles into Graafian follicles. The Graafian follicle is the final stage of follicular development before ovulation. Oocyte Preparation: During folliculogenesis (the process of follicle development), the oocyte (egg cell) accumulates essential resources, including: Mitochondria: Provides energy needed for cell functions. ATP: The primary energy currency of the cell, crucial for cellular processes. mRNAs and Proteins: Necessary for the early stages of embryogenesis, which is the period right after fertilization. Final Stages of Meiotic Maturation: The oocyte and the follicle are now ready for the final stages of meiotic maturation. This maturation process prepares the oocyte for ovulation and eventual fertilisation. Cumulus Oocyte Complex and Germinal Vesicle Stage Lecture 7: Female developmental reproduction 23  Germinal Vesicle (GV) Stage: The oocyte is still in the diplotene stage of Meiosis I, meaning it is arrested in its development. The nucleus at this stage is known as the germinal vesicle. Zona Pellucida: A glycoprotein layer surrounding the oocyte that plays a key role in fertilization. Luteinizing Hormone (LH) Surge and Meiotic Maturation LH Surge: A surge in Luteinizing Hormone (LH) triggers the oocyte to resume meiosis, leading to meiotic maturation. Cumulus Cells Expansion: The cumulus cells surrounding the oocyte expand and transform into a cloud-like structure. This change is crucial for ovulation. Polar Body Formation: As the oocyte undergoes asymmetric division during meiosis, it extrudes half of its nuclear material into a small structure known as the polar body. MII Oocytes MII Oocytes: The oocyte that is ready to be ovulated is referred to as a Metaphase II (MII) oocyte. This is the stage at which the oocyte is released from the ovary during ovulation. Polar Body: The polar body indicates that the oocyte has completed the first meiotic division and is now ready for fertilisation. Meiotic maturation Meiosis results in the production of a haploid gamete → It involves two sequential divisions: Meiosis I and Meiosis II (extra DNA is discarded) The resumption of meiosis in oocytes is triggered by the surge of Luteinizing Hormone (LH), which occurs just before ovulation. Key Steps in Meiotic Maturation 1. Germinal Vesicle Breakdown: The germinal vesicle, which is the nucleus of the oocyte at the GV stage, breaks down. This process involves the dissolution of the nuclear membrane. Lecture 7: Female developmental reproduction 24  2. Chromosome Alignment and Metaphase I Spindle Formation: Homologous chromosome pairs align at the metaphase plate of Metaphase I. A spindle apparatus forms to organize and separate the chromosomes. 3. Spindle Movement and Asymmetric Cell Division: The spindle moves to the oolemma (oocyte membrane), leading to an asymmetric cell division. This division produces a large secondary oocyte and a smaller polar body that contains half of the chromosomes from each pair. 4. Metaphase II Spindle Formation: After the first division, the secondary oocyte enters Metaphase II and arrests at this stage. The oocyte now has a Metaphase II spindle. 5. Completion of Meiosis at Fertilization: The oocyte remains arrested in Metaphase II until fertilization. Upon fertilization, it completes the second meiotic division, resulting in: Two Polar Bodies: Extruded during the second meiotic division. One Mature Ovum: Contains a single set of chromosomes, each with one chromatid. Timing In Mice: The transition from the LH surge to ovulation takes approximately 12 hours. In Humans: This process takes about 36 hours. Ovulation Lecture 7: Female developmental reproduction 25  Ovulation is a crucial process in reproduction, involving the release of a fully mature oocyte (also called an ovum) from the ovary (then picked up by the oviduct). This process ensures the oocyte is available for fertilisation. Triggering of Ovulation: Ovulation is triggered by a surge in luteinising hormone (LH), which is essential for the final stages of meiosis in the oocyte. Release of the Cumulus-Oocyte Complex: Only the cumulus-oocyte complex, consisting of the mature oocyte surrounded by cumulus cells, is expelled from the ovary during ovulation. The remainder of the follicle remains within the ovary. Formation of the Corpus Luteum: After ovulation, the remnants of the follicle transform into the corpus luteum. This transient endocrine gland secretes progesterone, which is crucial for maintaining the uterine lining and supporting pregnancy if fertilisation occurs. Primordial Follicles and Reproductive Lifespan: Follicular Attrition: Most primordial follicles do not progress to ovulation. Instead, they undergo atresia (degeneration) at various stages of follicular development. Oocyte Lifespan: Of the millions of germ cells present in the fetal ovary, only about 400 oocytes will eventually ovulate throughout a woman’s reproductive lifespan. Lecture 7: Female developmental reproduction 26  The development of an antral follicle through to a meiotically mature developmentally competent oocyte only occurs after puberty Lecture 7: Female developmental reproduction 27  Time course of follicle development The length of time it take to develop from a primordial follicle through to the larger antral follicle is species specific Occurs over 3 weeks in mice, 80-100 days in bovine and 4-6 months in humans BUT it only takes 36 hours to do the final stages of maturation and ovulation. Lecture 7: Female developmental reproduction 28 Lecture 7: Female developmental reproduction 29