development of amphioxus

8/11/2019 Development of Amphioxus

1/59

The Embryology Of The Amphioxus


2/59

Origins of Sex Cells

Section in a vertebrate

embryo showing the origin

of primordial germ cells. Stages of sexualdifferentiation


3/59

Types of eggs according the yolk distribution

Isolecithal (homolecithal)

Amphioxus

Telolecithal (Mesolecithal)

Frog

yolk

Telolecithal ( Macrolecithal, Megalecithal) Centrolecithal

Bony fish, reptiles, birds oviparous mammals Insects , Arthropods

yolk

yolk

Yolk

Germinal disc

( , 1 - , 12mm diameter) (1.216 mm diameter)

ChickBony fishs Insect egg


4/59

1 - Cleavage 2 blastulation 3 gastrulation 4

Organogesis

1 - Cleavage

Types of cleavage Plane of cleavage

Micromere

Macromere

Meroblastic,

discoidal, partial

(chick)

Holoblastic,

equal

(Amphioxus)

Holoblastic,

Unequal

(Frog)

2- blastomere 4 - blastomere

Latitudinal

Meridional

Holoblastic, equal(Mammal)

Blastoderm

yolk

Stages of the embryonic development


5/59

Amphioxus

Fish

Sturgeon)

Amphibia

Frog)

Reptilia

Turtle)

Bird

Chick)

Mammal

Man)

Shape of Sperms in Vertebrate Animal


6/59


7/59


8/59


9/59

Gene expression and protein synthesis

During development

-Cell behavior provides the link between

gene actionand developmental processes.-Genes control behavior by controlling which

proteinsare made by a cell.-Differential gene activity control

development.

- Development is progressive and the fate ofcells becomes determined at different times.

- As embryonic development proceeds the

organization complexity of the embryo

becomes vastly increased over that of the

fertilized egg.

- Differentialk gene activity controlsdevelopment.

- Inductive interactions can make cells

different from each cells.

- The response to inductive signalsdepends on

the state of the cell.


10/59

An inducing signal can be transmitted from one cell to

another in three main ways

1

DiffusionThe signal can be a diffusible

molecule, which interacts with a

receptor on the target cell surface.

2- Direct contact

The signal can be produced by

direct contact between two

complementary proteins at the cell

surfaces.

3

Gap junctionIf the signal involves smallmolecules it may pass directly from cell

to cell through gap junctions in the

plasma membrane.


11/59


12/59


13/59

Return chromosome number to

diploid value

Activation of development

Basic steps:Sperm activation/capacitation

Attraction of sperm to egg

Binding/passing through egg envelopeFusion of plasma membranes

Egg Activation

Fertilization

- Fertilization cone:

-Fusogenic

proteins

Bindin

Fertilin

- Nucleus,mitochondria, and

centriole all enter

the egg


14/59

FertilizationScanning electron micrograph of an egg

after the attraction of sperms.

Egg

Sperm

Sperm

Egg

Sperm

SEM showing the sperm

incorporation into egg.


15/59


16/59


17/59

Hypothetical pathway for calcium release

IP3 Inositol triphosphate

Dag diacylglycerol

PIP3 phosphatdidylinositol Triphosphate


18/59


19/59

Introduction

Embryologydeals with the development of the individual

from the fertilized egg or, in rare instances, from the unfertilized egg

to a stage resembling more or less closely the adult form.

Ontogeny is a broader and more comprehensive term thatincludes both the embryonic period and the entire postembryonicdevelopment of the individual to its adult condition.

In a general sense, ontogeny is the history of development of an

organism from the fertilized egg to sexual maturity.

Butterflies eggs Larvae (caterpillars) Pupa casesmetamorphosis

Butterflies

Marsupial mammals

(Kangaroo or opossum)

Immature embryo Postnatal in marsupial pouch


20/59

Reproduction

Multicellular animals

(Metazoa)

Sexual reproduction(syngamy)

Asexual reproduction(agamy)

Ex. Budding (Hydra)

Strobilization (Aurelia)

Constriction (annelid)

The new individual is produced not by

somatic cells of the parent but by sex

cells, or gametes (sperm from male andovum from femal) which differ essentially

from somatic cells in having undergone

meiosis a process in which the number of

chromosomes is reduced to one-half of

the diploid (2n) number found in somatic

cells. Furthermore, the sex cells are

generally capable of developing into a

new individual only after two have united

in a process called fertilization.

( eggs develop without fertilization)

invertebrate animals (honeybee)

Produced from fertilized eggs

drones Produced from unfertlized eggs

The new individual is derived from a

blastem ( a group of cells from the

parent body)

Chromosomes of the blastema is the

same as in the other somatic cells ofthe parent (diploid set) 2n.

Workers and Queens

Daphnia

honeybee

Parthenogenesis


21/59

O

vu

Spermatogenesis

Oogenesis

Both include:

Reduction in

chromosome number

by meiosis

Acquisition of

structural and

functional characters

Gametogenesis

Ootid


22/59


23/59

Mitosis Review

ProphaseInterphase

AnaphaseMetaphase

Telophase


24/59


25/59

Prophase I

Leptotema

Zygonema

Pachynema**

Diplonema**

Diakenesis

Meiosis Review

Meiosis I


26/59

Anaphase I and Telophase I

Metaphase


27/59

Meiosis II


28/59


29/59


30/59


31/59

The ovulation in human


32/59

Types of stem cells1-Embryonic stem cells (ES cells)Totipotent stem cells Only the morula s cells are totipotent, able to

become all tissues and a placenta

-Pluripotent stem cells, originate as inner cells within a blastocyst and

they can become any tissue in the body, excluding a placenta.-Human embryos reach the blastocyst stage 4-5 days post fertilization,at which time they consist of 50-150 cells.

-They are able to differentiate into all derivatives of the three primary

germ layers: ectoderm, endoderm, and mesoderm.

-Multipotent stem cells Stem cells can produce only cells of a closely

related family of cells (e.g. hematopoitic stem cells differentiate intored blood cells, while blood cells, platelets. Etc.).

-2-Adult stem cells


33/59


34/59

Eggs of amphioxus are released by rupture of follicular membranes and overlyingtissues so that then find their way first into the atrium and then via the atriopore

into the sea. By this time the first polar body has been separated off and comesto lie just outside the thin vitelline membrane.

The egg of Amphioxus

Second

polar

body

First polar bodyNucleolus

Nucleus

Yolk

Unfertilized egg Fertilized egg

AcrosomeHeadTail

Cenriole

The sperm of Amphioxus


35/59

Fertilization inAmphioxus

After the entry of the sperm into the

egg cytoplasm the egg nucleus

completes its maturation division and

the second polar body is extruded.

Scheme of maturation, syngamy,

karyogamy of the ovum.


36/59

polar bodies

Polar body

2

Blastomere stage

Cleavage

( 2 blastomere stage)

Holoblastic division

Plane is latitudinal

First cleavage


37/59

4 and 8 blastomere stage

Plane of

division is

latitudinal

Plane ofdivision is

latitudinal

(vertical)

Vertical at right angle to the

first two and passes through

just above the equater

Micromere

Macromere


38/59


39/59

Blastulation in Amphioxus

T.S of the blastulaThe meridional cleavage of the sixth

division give a total of 64- cells and after

this stage the cleavages become some

what irregular .

Blastula

from side

W. M. of the blastula

Micromere

Blastocoel

Blastocoel


40/59

The blastula of amphioxus

and its change in polarity

during gastrulation

The gastrula of amphioxus

with a remnant of theblastocoel still present at the

blastopore


41/59

Gastrulation in Amphioxus

Sagittal half of an early

gastrula

Sagittal half of a later gastrula


42/59

Sagittal half of a completed gastrula Dorsal half of a completed gastrula

Gastrulation in Amphioxus

Longitudinal section of a post

gastrula stage


43/59

Gastrula of Amphioxus showing

progressive overgrowth of the the

ectoderm over the blastopore in

the formation of the neural folds


44/59


45/59

Formation of the neural tube

T. s. and Stereogram of a part of a post-gastrulation stage.

T. S. to show the

separation of the

mesodermal

pouches

T. S. of a larva to

show the formation

of the coelom.

Stereogram to show

the arrangement of

the mesodermal

pouches.


46/59

The gastrula of amphioxus.

The ectoderm has grown

over the blastopore in the

formation of the neurocoel.

The passage between theneurocoel and the

archentron is the neuroentric

canal.


47/59

Amphioxus embryo with the neural tube, the notochord and the

mesodermal somites differentiated.

Longitudinal

section of a post

gastrula stage of

Amphioxus


48/59

Young larvae of Amphioxus

Optical view of a young larva from the

dorsal aspect

Larval stage after opening of mouth and 3

gill slits.

Larval stage after opening 4 gill slits.

Embryo with the anterior gut diverticulum

Three gill slits

Four gill slits


49/59

Fourteen somite larva of Amphioxus

Partly dissected young Amphioxus


50/59


51/59


52/59

Gonads

A B

AB

Schematic section through the pharynx

of Amphioxus with special emphasis on

the mesodermal differentiation


53/59


54/59

Diagrammatic transverse section through the larva of

Amphioxus during the formation of the atrium


55/59


56/59


57/59


58/59

NucleusBlood vessels

OocyteFollicle cells

Stroma

A section of the ovary of the

frog containing young oocytes.

All nuclei are stll located in the

center of the oocytes and very

little yolk has been formed.


59/59

development of amphioxus

Documents