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Developmental Biology > Unit 2: Gametogenesis, Spermatogenesis, Oogenesis > Flashcards

Unit 2: Gametogenesis, Spermatogenesis, Oogenesis Flashcards

1
Q

It is often the case that the future germ cells become committed to their fate at an early stage of animal development

In some cases, there is a cytoplasmic determinant present in the egg that programs cells that inherit it to become germ cells

In humans and other mammals, a complex interplay of hormones regulates

The process of _______ is based on meiosis, but differs in females and males
The critical cellular event in gamete production

Modified type of cell cycle in which the number of chromosomes in reduced by half

A

A. Gametogenesis

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2
Q

This is associated with a visible specialization of the cytoplasm called

A

germ plasm

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3
Q

Production of mature sperm cells

Primary spermatocytes undergo meiosis

One primary spermatocyte produces four haploid spermatids

Spermatids–23 chromosomes

late spermatids are produced with distinct regions

Sperm cells result after maturing of spermatids

Spermatogenesis takes 64 to 72 days

A

Spermatogenesis

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4
Q

undergo rapid mitosis to produce more stem cells before puberty

A

Spermatogonia

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5
Q

modifies spermatogonia division
 Type A daughter cell
 Type B daughter cell

A

Follicle-stimulating hormone (FSH)

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6
Q

It is the development of mature ova

A

Oogenesis

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7
Q

Oogenesis It differs from spermatogenesis in three major ways:

A
  1. During the meiotic divisions of oogenesis
  2. Sperm are produced continuously throughout a male’s life
  3. It has long “resting” periods
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8
Q

Male and Female Differences

A

Meiosis
Sex cell size and structure

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9
Q

Male and Female Differences
Meiosis

A

 Males produce four functional sperm
 Females produce one functional ovum and three polar bodies

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10
Q

Sex cell size and structure Male and Female Differences

A

 Sperm are tiny, motile, and equipped with nutrients in seminal fluid

 Egg is large, non-motile, and has nutrient reserves to nourish the embryo until implantation

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11
Q

D. Structure of the Gametes
Parts of mature sperm:

A
  • Head – haploid nucleus, little cytoplasm, Acrosome
  • Neck/Midpiece – Mitochondria, centriole
  • Tail (or propulsion system) some species – ameboid motion
     Most sperm are propelled by flagella
     Formed by microtubules
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12
Q

 Must allow sperm to travel long distance, using plenty of energy
 Axoneme: motor portion
 Microtubules in a 9+2 configuration

A

Flagella Structure

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13
Q

 Upon release, mammalian sperm are able to move, but do not have yet the capacity to bind an egg
 Must enter the female reproductive tract to complete the last step of the maturation process (Capacitation) and acquired the ability to bind the egg

A

Sperm Capacitation

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14
Q

stores all material for beginning of growth and development
 Unlike sperm, the ____ conserves and acquires more cytoplasm as it matures

A

 Ovum (mature egg)

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15
Q

 Parts of the egg:

A
  • Cytoplasm – many components
  • Haploid nucleus
  • Cell membrane will fuse with sperm plasma membrane
  • Extracellular envelope
     Vitelline envelope contains glycoproteins essential for species specificity and sperm biding
  • Cortex: beneath the cell membrane
  • Cortical granules: inside cortex
  • Egg jelly (some species): attract/activate sperm
  • Zona pellucida (mammals) extra coating made of extracellular matrix
  • Cumulus (mammals): layer of cells that nurture the egg innermost layer is called Corona Radiata
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16
Q

Fusion of two gametes to create a new individual, with a genome different from both parents.

A

Fertilization

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17
Q

2 Major Goal of Fertilization

A

 Joining of genetic material to create new variations (sex)
 Creation of a new organism (reproduction)

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18
Q

Four Major Events of Fertilization:

A
  1. Sperm and egg make contact and must recognize each other as the same species
  2. One (and only one) sperm enter egg
  3. Fusion of the genetic material
  4. Activation of egg to begin development
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19
Q

Recognition of Sperm and Egg

A
  1. Chemoattraction
  2. Exocytosis
  3. Binding
  4. Passage
  5. Fusion
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20
Q

External Fertilization: two mechanisms have evolved to address these issues:
 Species-specific attraction of sperm
 Species-specific sperm activation

A

Step 1: Chemoattraction (Sea-Urchin Model)
Step 2: Acrosome Reaction (Sea-urchin Model)

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21
Q

 Sperm attraction: Action at a distance
 Sea urchin have reacted peptide in the egg jelly of the egg
* 14 amino-acid peptide and can diffuse in sea water
* Attracts sperm to egg and acts as a sperm-activating peptide
* Increases sperm motility and mitochondrial production of ATP

A

Step 1: Chemoattraction (Sea-Urchin Model)

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22
Q

Acrosome Reaction (Sea-urchin Model)
 Two components

A
  1. The fusion of the acrosomal vesicle with the sperm cell membrane
  2. The extension of the acrosomal process
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23
Q

 Initiated by species-specific compounds in the egg jelly
 Compounds bind to receptors on sperm cell membrane
 Calcium channels open; calcium flows into sperm head
 This induces fusion of the acrosomal membrane with sperm cell membrane

A
  1. The fusion of the acrosomal vesicle with the sperm cell membrane
24
Q

 Polymerization of globular actin molecules into actin filaments

A
  1. The extension of the acrosomal process
25
Q

 Acrosomal process is important for species-specific recognition
 In S. purpuratus the acrosomal process contains a protein called bindin
 This bindin can bind to the surface of S. purpuratus egg but not S. franciscanus
 Bindins of closely related sea urchin species have different protein sequences
 Needed to tether the sperm to the egg
 Eggs will adhere only to the bindin of their own species
 Sperm attraction, sperm activation, the acrosome reaction, and sperm adhesion to the egg surface

A

Recognitions of the Egg Extracellular Coat

26
Q

 Sperm-egg fusion appears to cause polymerization of actin in the egg to form a fertilization cone
 Fusion is an active process, often mediated by specific “fusogenic” proteins
* Bindin can cause the sperm and egg membrane to fuse

A

Fusion of Egg and Sperm Cell Membrane

27
Q
  • Restores the diploid chromosome number
  • Sperm centriole become the mitotic spindle
A

Monospermy is the norm

28
Q
  • Results in triploid nucleus
  • Multiple mitotic spindles form
A

Polyspermy is disastrous

29
Q

 The egg has a different ionic concentration from the seawater in which it exists
 Egg has lower sodium ion concentration; higher potassium concentration
 This is maintained by sodium/potassium pumps in the egg cell membrane
 The difference in charge across the egg membrane can be measured as -70mV and is called the resting membrane potential
 Polyspermy can be included if an electric current is applied to artificially keep the sea urchin egg membrane potential negative
 Fertilization can be prevented entirely by artificially keeping the membrane potential of eggs positive

A

The Fast Block to Polyspermy

30
Q

 Slower, mechanical, permanent block
 Occurs about a minute after sperm-egg fusion
 Upon sperm entry cortical granules with the cell membrane and release several molecules
 Elevated from the cell membrane by mucopolysaccharides release by the cortical granules
* Stabilized by crosslinking adjacent proteins

A

The Slow Block to Polyspermy

31
Q

 Upon fertilization, the concentration of free Ca2+ in the egg cytoplasm increases greatly
 In sea urchins and mammals, the rise in Ca2+ concentration responsible for the cortical granule reaction is not due to an influx of calcium into the egg, but comes from within the egg itself
 Ca2+ is directly responsible for propagating the cortical granule reaction, and that these ions are stored within the egg itself
 A23187 is a calcium ionophore transports Ca2+ across lipid membranes
 Placing sea urchin embryos in sea water containing A23187 results in cortical granule reaction & fertilization envelope to rise
 If Ca2+ chelator is injected into egg, no cortical reaction occurs

A

Calcium as the initiator of the cortical granule reaction

32
Q

 Fertilization is often depicted as nothing more than the means to merge two haploid nuclei; it has an equally important role in initiating the processes that begin development
 Release of intracellular calcium ions: the way Ca2+ is released varies from species to species
 IP3: the releaser of Ca2+
* Inositol 1,4,5-triphosphate (IP3): primary agent for releasing Ca2+ from intracellular storage
* IP3-responsive calcium channels, found in the egg endoplasmic reticulum

A

Activation of Egg Metabolism in Sea Urchins

33
Q

Phospholipase C: The Generator of IP3

A
  1. There are numerous types of PLC
  2. Can be activated through different pathways, and
  3. Different species use different mechanism to activate PLC
34
Q

Effects of Calcium Release

A
  • The flux of calcium across the egg activates a preprogrammed set of metabolic events
  • Early and Late Response
35
Q

 The fast block, mediated by sodium influx into the cell
 Cortical granule reaction, or slow block, mediated by the intracellular release of Ca2+
 Calcium release activates a series of metabolic reactions that initiate embryonic development

A

Effects of Calcium Release: Early Responses

36
Q

 The late responses of fertilization include the activation DNA and protein synthesis
 In sea urchins, the fusion of egg and sperm causes the intracellular pH to increase
 pH increases and Ca2+ elevation – DNA and protein synthesis
 Calcium ions – DNA synthesis
 In sea urchin, a burst protein synthesis usually occurs within several minutes after sperm entry
 Mitosis-promoting factors (MPF)

A

Effects of Calcium Release: Late Responses

37
Q

 After the sperm and egg cell membranes fuse, the sperm nucleus and its centriole separate from the mitochondria and flagellum
 Fertilization in sea urchins’ eggs occurs after the second meiotic division, so there is already a haploid female pronucleus present when the sperm enters the egg cytoplasm
 After the sea urchin enters the egg cytoplasm
 The sperm nucleus separates from the tail
 Rotates 180° so that the sperm centriole is between the developing male pronucleus and the egg pronucleus

A

Fusion of Genetic Material in Sea Urchin

38
Q

Difficulties in studying interactions between the mammalian sperm ad egg prior to these gametes making contact

A
  1. Mammalian fertilization occurs inside the oviducts of the female
  2. The sperm population ejaculated inside into the female is probably heterogeneous, containing spermatozoa at different stages of maturation
  3. There may be multiple mechanism by which mammalian sperm can undergo the acrosome reaction and bind to the zona pellucida
39
Q

Getting the gametes into the oviduct

A

Translocation

40
Q

getting sperm through the cervical mucus and into the uterus

A

 Sperm motility

41
Q

sperm transported to the oviduct

A

Uterine muscle contractions

42
Q

migrate against the direction of the flow

A

Sperm rheotaxis

43
Q

the change undergone by sperm in the female reproductive tract that enable them to penetrate and fertilize an egg

A
  • Capacitation
44
Q

the sperm cell membrane is altered by the removal of cholesterol by albumin proteins in the female reproductive tract

A
  • Lipid changes
45
Q

particular proteins or carbohydrates on the sperm surfaces are lost during capacitation
* There may be an important connection between sperm translocation and capacitation
* The life span of the sperm is significantly lengthened by this binding

A
  • Protein changes
46
Q

they swim at higher velocities and generate greater force
 Mediated by the opening of a sperm-specific calcium channel in the sperm

A

Hyperactivation

47
Q

sperm to digest a path through the extracellular matrix of the cumulus cells

A

Hyaluronidase enzyme

48
Q
  • Ability to sense temperature difference and preferentially swim from cooler to warmer sites
  • Found only in capacitated sperm
  • 2°C between the isthmus of the oviduct and the warmer ampullary region
A

Thermotaxis

49
Q

secrete molecules that attract capacitated sperm toward the egg

A

Chemotaxis

50
Q

made by the cumulus cells, as a directional cue

A

Progesterone

51
Q

plays a role analogous to that of the vitelline envelope in invertebrates
 Zona is a far thicker and denser structure
 Mouse – ZP1, ZP2, and ZP3
 Human – ZP1, ZP2, ZP3, and ZP4

A

zona pellucida

52
Q
  • ZP2 was shown to be critical for human sperm-egg binding
  • ZP3 was the other candidate for binding sperm
     Evidence is shown in mice and humans
A

The acrosome reaction and recognition at the zona pellucida

53
Q

 Mammals: side of the sperm head makes contact with the egg
 Equatorial region where the membrane fusion between sperm and egg begins
 Izumo originally found in the membrane of the acrosomal granule
 Sperm-egg binding proteins
 Binds to an oocyte protein called Juno
o CD9 involved with sperm-egg fusion
 ZP2 is clipped by the protease ovastacin and loses its ability to bind sperm
 Ovastacin is found in the cortical granules of unfertilized eggs

A

Gametes fusion and the prevention of polyspermy

54
Q

 The DNA of the sperm pronucleus is bound by protamines
 Calcium oscillations brought about by sperm entry inactivate MAP kinase and allow DNA synthesis
* Activate another kinase and securin
 DNA synthesis occurs separately in the male and female pronuclei
 Each sperm brings its nucleus mitochondria, its centriole, and a tiny amount of cytoplasm
 Sperm centriole serve as the organizing agent for making the new mitotic spindle

A

Fusion of genetic material

55
Q

 Rise in cytoplasmic Ca2+ is necessary for an egg activation in mammals
 In sea urchins, fertilization triggers intracellular Ca2+ release through the production of IP3 by the enzyme phospholipase
 Mammalian PLC responsible for egg activation and pronucleus formation come from the sperm
 Activator of Ca2+ release was stored in the sperm head
 In mice, expression of PLC (gamma) mRNA in the egg produces Ca2+ oscillations
 In mammals, the Ca2+ release by IP3 binds toa series of proteins including calmodulin-activated protein kinase, MAP kinase and synaptotagmin

A

Activation of the mammalian egg

56
Q

Fertilization is not a moment or an event, but a process of carefully orchestrated and coordinated events including the contact and fusion of gametes, the fusion of nuclei, and the activation of development

A

Coda

Developmental Biology (2 decks)

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