[1] Amphibian oogenesis

the ovaries of the frogs are ___ organs suspended into the body cavity by the ___

paired hollow; mesovarium

there are ___ to ____ lobes in each ovary which is greatly distended with ____ during breeding season

7; 12; eggs

it takes ___ years for the frog’s eggs to develop to maturity

three

three phases of frog’s eggs development

• multiplication of the oogonia

• meiosis and growth

• quiescent retention in the ovary

under the influence of the _____ and stimulated by ____, the eggs are released ___, a process called _____

pituitary gland hormones; amplexus; en masse; ovulation

• outermost covering of the ovary composed of thin connective tissue

• continuous with the mesovarium and the outer membrane of the egg cells.

theca externa

Theca Externa – outermost covering of the ovary composed of ___ . Note that it is continuous with the ___ and the ___ of the egg cells

thin connective tissue; mesovarium; outer membrane

thin membrane surrounding the egg cells and continuous with the theca externa. It is composed of a single layer of muscle cells.

theca interna

Theca Interna – thin membrane surrounding the egg cells and continuous with the ___. It is composed of a single layer of ___

theca externa; muscle cells

a layer of spindle-shaped cells inner to the theca interna. They serve as nurse cells to the oocyte.

follicle cells

Follicle Cells - a layer of ___ cells inner to the ___. They serve as ___ to the oocyte

spindle-shaped; theca interna; nurse cells

• very large, round or oval cells with equally large nucleus.

• These cells are in the prolonged prophase I and are active in the synthesis of molecules that are stored in the cytoplasm.

• Most are so large (200 – 350 µm) that a scanner (4x) of the microscope must be used to see the entire cells

• The cells are easily distinguished by their sizes and staining affinities.

oocytes

Oocytes – very large, round or oval cells with equally large ___. These cells are in the prolonged ___ and are active in the synthesis of molecules that are stored in the cytoplasm. Most oocytes are so large (200 – 350 µm) that a ___ of the microscope must be used to see the entire cells. The cells are easily distinguished by their ___ and ___

nucleus; prophase I; scanner (4x); sizes; staining affinities

what are the components of the oocytes

• cytoplasm

• germinal vesicle

• nucleoli

• vitelline membrane

• a large, homogenous area containing abundant yolk concentrated at the periphery and around the nucleus of the cell. The yolk appears as granular bodies which represent the stored food for the future embryo

• may stain lightly in larger cells or bluish violet in smaller cells.

cytoplasm

Cytoplasm – a large, ___ area containing abundant ___ concentrated at the periphery and around the ___ of the cell. The yolk appears as ___ which represent the stored food for the future embryo. The cytoplasm may stain ___ in larger cells or ___ in smaller cells.

homogenous; yolk; nucleus; granular bodies; lightly; bluish violet

what is the composition of the yolk

• lipids, proteins, vitamins, minerals for nutrition

• yolk platelets composed of phosvitin and lipovitelline

• special name for the enlarged nucleus of the frog’s oocyte

• When viewed, some oocytes may have smaller or even none at all

germinal vesicle

Germinal Vesicle – special name for the ___ of the frog’s oocyte. When viewed, some oocytes may have smaller or even no germinal vesicle at all

enlarged nucleus

why do some oocytes have smaller or even no germinal vesicle

• maturity of oocyte

• germinal vesicle breaks down during maturation due to disintegration of nuclear envelope

small but numerous dense bodies at the periphery of the nuclear membrane. They appear as black dots of varied sizes. This is a unique feature of the frog’s oocytes.

nucleoli

Nucleoli – small but numerous ___ at the periphery of the ___. They appear as ___ of varied sizes. This is a unique feature of the frog’s oocytes.

dense bodies; nuclear membrane; black dots

a thin, non-cellular layer immediately surrounding the oocyte and inner to the follicle cells.

vitelline membrane

Vitelline membrane – a thin, non-cellular layer immediately surrounding the ___ and inner to the ___

oocyte; follicle cells

what is the fate of the vitelline membrane after fertilization

• transforms into the fertilization membrane: elevates and hardens due to cortical granules released from cortex of egg

  • prevents additional sperm from entering the egg

cluster of small cells with large nuclei and intensely basophilic cytoplasm.. These are fewer in number and are found at the periphery of the ovary. Sometimes, they are totally absent

oogonia

Oogonia – cluster of small cells with ___ and intensely ___ cytoplasm. These are fewer in number and are found at the ___ of the ovary. Sometimes, they are totally absent.

large nuclei; basophilic; periphery

why are the oogonia sometimes totally absent

• may have already developed into oocytes

• transitioned into the primary oocyte stage

what is the functional significance of the numerous nucleoli of the oocytes? of the yolk?

• survive longer outside of the mother by conserving its energy

• allow longevity through reduced biogenesis

• yolk functions as a reservoir of nutrients and raw materials

what might account for the difference in the staining affinity of the small from the larger cells

• larger cells are actively synthesizing cytoplasmic molecules: higher affinity for dye

• arrested at prophase I

nutrient source of sperm cells

seminal fluid

nutrient source of oocytes

yolk

location of nucleus of sperm cells

below the acrosome

location of nucleus of oocytes

centrally located

ploidy of sperm cells

haploid

ploidy of oocytes

haploid, but arrested at meiosis II before fertilization

protective envelope of sperm cells

none

protective envelope of oocytes

vitelline membrane

location of enzymes for fertilization in sperm cells

acrosomal vesicle

location of enzymes in oocytes

cortical granules

motility of sperm cells

motile using a flagellum

amphibians exhibit ____ fertilization. They can produce several offspring without the use of too much energy for nutrient production

external

the egg is released in water or _____ is formed above water

bubble case

the egg is released from the ____ to the ____

peritoneal cavity; cloaca

amphibian oogenesis produces ___ eggs but with ____ lifespan

more; shorter

oogenesis can be done _____

throughout the life cycle

3 phases of development of the Amphibian egg

• previtellogenesis

• vitellogenesis

• final maturation

annual egg generation by ___ from ___ and annual release

mitosis; gametogenic stem cells

• up to early diplotene of mitosis

• organelle development: mitochondria, size of nucleus (germinal vesicle)

• RNA synthesis

• formation of large numbers of nucleoli: specific gene amplification, adaptive response to increase amount of ribosome

previtellogenic phase

• deposition of yolk in cytoplasm

• stored protein (yolk platelets), lipid (lipochondria), and carbohydrates (glycogen granules)

• vitellogenin

vitellogenic phase

vitellogenin is a yolk protein composed of:

• lipovitellin

• phosphovitin

• hormonal induction of eggs from the first meiotic block

• breakdown of germinal vesicles: mixing of nucleoplasm and cytoplasm for cleavage

• completion of MI

• formation of 1st polar body

maturation phase

ovary containing cells enclosed by sac made up of two membranes:

• theca externa

• theca interna

upon maturation:

• accumulation of yolk

• synthesis of RNA

• increase in size

ovulation: oocyte ovulated through ___ into . ___oogonial clusters remain as reserved sources of ____

theca externa; abdominal cavity; oocytes

Biological process by which diploid or haploid cells undergo cell division and differentiation to form mature haploid gametes

gametogenesis

gametogenesis occurs by ___ of diploid gametocytes into various gametes

meiotic division

functions of gametes: to ___ in environment quite different from that of the gonad

survive

functions of gametes: to recognize ____ of the other gender and participate in events related to ___

homologous cells; fertilization

functions of gametes: to provide sufficient ____ to support development of a new organism

genetic and cytoplasmic materials

gametogenesis

counterpart of spermatogenesis in the female animal

oogenesis

oogenesis: Starts in the ___ and is completed while the primary oocyte is on its way to the ____ or in the ____ during ___ of the mature ovum

embryo; fallopian tube; fallopian tube; fertilization

___ are not seen in the ovary because they have differentiated into ___ even before birth of the fetus

Oogonia; primary oocytes

Only the ___ are present in the ovary: Each is contained in the ___ that grows and eventually ruptures during ___ to release it

primary oocytes; ovarian follicle; ovulation

During ___, primary oocyte divides into a ___ and a ___

ovulation; secondary oocyte; 1st polar body

The secondary oocyte divides into an ___ and a ___ during ___ in the fallopian tube

ovum; 2nd polar body; fertilization

what are the types of ovum

• microlecithal egg

• mesolecithal egg

• macrolecithal egg

amount of yolk of microlecithal egg

scanty

yolk distribution of microlecithal egg

isolecithal: equal distribution

microlecithal egg is found in:

placental mammal

amount of yolk in mesolecithal egg

moderate amount

yolk distribution in mesolecithal egg

increasing gradient from animal to vegetal pole

mesolecithal egg is found in:

amphibians

amount of yolk in macrolecithal egg

large amount

yolk distribution in macrolecithal egg

telolecithal: at vegetal pole

macrolecithal egg is found in:

bird

Small, centrally located nucleus

microlecithal ovum

microlecithal ovum: Enclosed by inner ___ and outer ___ separated by a tiny ___

plasma membrane; vitelline envelope; perivitelline space

microlecithal ovum: Vitelline envelope is surrounded externally by the ___, a glycoprotein layer (ZP1, ZP2 and ZP3) secreted by the ___ and ___ (single layer of follicular cells)

zona pellucida; vitelline membrane; corona radiata

functions of the zona pellucida

• species-specific sperm penetration

• permanent block to polyspermy

• porous selective filter

• immunologic barrier

• keeps blastomere together

• prevents premature implantation

• Large and presents an animal pole where the nucleus is located and an opposite vegetal pole where the yolk is concentrated

• Nucleus is located at the animal pole of the ovum

• Absence of zona pellucida but with a vitelline membrane

macrolecithal egg

section through part of the ovary of a frog tadpole

section through part of the ovary of a frog tadpole

section through the sacculate ovary of an adult frog

Section through an area of an adult frog ovary showing growing oocytes

section through a large frog primary oocyte

Section through a mature frog primary oocyte

Section through a mature frog primary oocyte

frog ovary section showing growing oocytes