Fertilization: Beginning a New New Organism Or

Transcription

1 Fertilization: Beginning a New Organism

2 1. Contact and recognition between sperm and egg. In most cases, this ensures that the sperm and egg are of the same species. 2. Regulation of sperm entry into the egg. Only one sperm can ultimately fertilize the egg. This is usually accomplished by allowing only one sperm to enter the egg and inhibiting any others from entering. 3. Fusion of the genetic material of sperm and egg. 4. Activation of egg metabolism to start development.

3 Initial observations of sperm and views of germ cells function (17C) Sperm had been accepted as one of the parasites (Spermatozoa) Sperm acts like a seed that t contain all vital information, while egg provides nutrients grow sperm s vital information. Homunculus (Figure 7.1) Revisiting the function of sperm in reproduction (19C) Spallanzani suggested that sperm itself is not enough, while egg contains all information that can be activated by sperm. Prevost and Dumas found sperm enters into egg and contribute materially to the next generation. In late 1800 s, Hertwig and Fol observed the union between sperm and egg s nuclei. The human infant preformed in the sperm, as depicted d by Nicolas Hartsoeker (1694).

4 The statue to Spallanzani has him examining a frog through a magnifying g glass.

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6 The modification of a germ cell to form a mammalian sperm (Part 1)

7 The modification of a germ cell to form a mammalian sperm (Part 2)

8 The modification of a germ cell to form a mammalian sperm (Part 3)

9 The modification of a germ cell to form a mammalian sperm (Part 4) Acrosome (Proacrosin-GFP) Nucleus/mitochondria/mictotubule

10 The motile apparatus of the sperm 9+2 structure

11 The motile apparatus of the sperm (Part 2) The movements of cilia and flagella result from the sliding of outer microtubule doublets relative to one another, powered by the motor activity it of the axonemal dyneins. Dyneins provide driving force for microtubules and vend the flagella with their ATPase activity.

12 Movement of microtubules in cilia and flagella Kartagener triad

13 Proteins Ribosomes and trna Messenger RNA Morphogenetic p g factors Protective chemicals. Structure of the sea urchin egg during fertilization. The drawing also shows the relative sizes of egg and sperm. (After Epel 1977.)

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15 The sea urchin egg cell surface.

16 Hamster eggs immediately before fertilization.

17 1. The chemoattraction of the sperm to the egg by soluble molecules secreted by the egg 2. The exocytosis of the acrosomal vesicle to release its enzymes 3. The binding of the sperm to the extracellular l envelope (vitelline layer or zona pellucida) of the egg 4. The passing of the sperm through this extracellular envelope 5. Fusion of egg and sperm cell plasma membranes

18 External Fertilization in Sea Urchins How can sperm and eggs meet in such a dilute concentration? ---species-specific attraction of sperm How can sperm be prevented from trying to fertilize eggs of p p y g gg another species? ---species-specific sperm activation

19 20 s 40 s Figure Sperm chemotaxis in Arbacia. 60 s 70 s 90 s Effect of 10 nm resact on A. punctulata tlt spermatozoa

20 Comparison of the effects of (a)100 nm resact and (b)10 m speract on A. punctulata p ( ) ( ) p p spermatozoa.

21 Model for chemotactic peptides in sea urchin sperm

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23 Fusion Extension Acrosomal reaction in sea urchin sperm.

24 Species-specific binding of acrosomal process to egg cell surface in sea urchins.

25 Localization of bindin on the acrosomal process.

26 Bindin receptors on the egg.

27 Bindin receptors on the egg (Part 2)

28 Scanning electron micrographs of the entry of sperm into sea urchin eggs.

29 Aberrant development in a dispermic sea urchin egg (Part 1) Why can only one sperm enter into the egg? To prevent improper numbers of chromosomes in daughter cells.

30 Aberrant development in a dispermic sea urchin egg (Part 2)

31 Membrane potential of sea urchin eggs before and after fertilization

32 Membrane potential of sea urchin eggs before and after fertilization 490 mm Na mm Na+

33 Formation of the fertilization envelope and removal of excess sperm

34 Cortical granule exocytosis (Part 1)

35 Cortical granule exocytosis (Part 2)

36 Cortical granule exocytosis (Part 3)

37 Wave of calcium release across sea urchin eggs during fertilization.

38 Endoplasmic reticulum surrounding cortical granules in sea urchin eggs.

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41 Model of possible pathway of egg activation in the sea urchin.

42 The roles of inositol phosphates in releasing calcium from the endoplasmic reticulum and the initiation of development

43 A burst of protein synthesis at fertilization uses mrnas stored in the oocyte cytoplasm.

44 Fusion of genetic material Sperm s nucleus and centriole separate from the mitochondria and dflagellum. ll The sperm nucleus undergoes dramatic decondensation to form pronucleus. Nuclear envelope vesiculates into small packets, and the sperm s s proteins associated with condensed chromosomes are exchanged by egg s to decondensate chromosomes. Phosphorylation of lamin and histones by PKA after the binding to glycoprotein in the egg jelly. Rotation of male pronucleus results in the localization of centriole between male and female nuclei

45 Nuclear events in the fertilization of the sea urchin (Part 1)

46 Nuclear events in the fertilization of the sea urchin (Part 2)

47 Nuclear events in the fertilization of the sea urchin (Part 3)

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50 1. The sperm cell membrane is altered by the removal of cholesterol l byalbumin proteins ti in the female reproductive tract. 2. Particular proteins or carbohydrates on the sperm surface are lost during capacitation. 3. The membrane potential of the sperm cell membrane becomes more negative as potassium ions leave the sperm. 4. Protein phosphorylation h occurs. 5. The outer acrosomal membrane changes and comes into contact with sperm cell membrane in a way that prepares it for fusion.

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52 Mouse ZP3 as the zona protein that binds sperm.

53 Acrosomal reaction in hamster sperm.

54 Entry of sperm into golden hamster egg.

55 Nature 434, (10 March 2005)

56 Fusion of genetic materials Sperm pronucleus migrate tangentially to the surface of the egg Glutathione in the egg cytoplasm reduces disulfide bonds among protamines to uncoil sperm chromosome. Proteolysis of cyclin B and securin, with the subsequent degradation of cohesin holding metaphase chromosomes, is induced by Ca2+ release. The rest of sperm components in fertilized egg cytoplasm, such as mitochondria and other trace cytoplasmic content, except centromere is degraded d d

57 Pronuclear movements during human fertilization

58 Summary of events leading to fusion of egg & sperm plasma membranes