Embryology

1. EMBRIOLOGIA
&
CICLO CELULAR
JUAN CARLOS MUNEVAR

2. APPLICATIONS OF
MITOSIS AND MEIOSIS

3. A Characteristic of Living things
Growth, Division, Reproduction

4. New Terms:
• Development – progress through lifetime
• Growth – increase in size, volume, mass
• Morphogenesis – development of shapes
• Epigenesis – development from a formless zygote
• Differentiation – cells become different from each
other
• Determination – fate of cells is set (before
differentiation), usually at gene control level
• Induction – One tissue or substance causes
determination, then differentiation, of other cells

5. APOPTOSIS

6. EVOLTUION OF EMBRYOS
•Requires multicellularity
•Only becomes embryology when
cells are differentiated.
•Follows a common pattern in the
Animal Kingdom

8. Stages in Embryology
Animal Examples

9. The Egg
• Large, sessile gamete
• Yolk – the phospholipid lecithin
• Haploid nucleus (notice timing for humans
and Ascaris)
• Oolemma – two membranes plus jelly layer
• Jelly layer -- Hyaluronic Acid and Proteins
• Cortical granules – vesicles in cortex

11. The Sperm
• Small, motile gamete
• Flagellated in animals and lower plants
• Haploid nucleus
• Acrosome – specialized cytoplasmic vesicle
for digesting jelly layer (hyaluronidase and
proteases) and for attaching to Oolemma
(bindin)

12. Fertilization
• Sperm activated by egg hormones
(gynagamones)
• Formation of Acrosomal Process
(microfilaments)
• Release of hyaluronidase and proteases
• Bindin attach to bindin recognition site on
oolemma

17. Egg Activation
• Depolarization of membrane
• Evacuation of cortical granules
• Elevation of vitelline membrane (separation
of vitelline membrane from egg cell
membrane in oolemma)
• Blocking of all other bindin sites
• Activation of metabolism in cytoplasm
• Completion of meiosis in some organisms

19. Early cleavage
• First cleavage – Two-cell stage
• Second cleavage – Four-cell stage
• Additional cleavages in ball shape
• Morula
• Blastula – first morphogenetic movements
(cells migrate to form hollow ball)
• Blastocoel (space) and Protoderm (tissue)

26. Gastrulation
• Second Morphogenetic step (first is
formation of the blastula).
• Tissues MOVE relative to each other and
relative to their position in the embryo!
• Different cells move different amounts and
change shape by different amounts.
• Protein gradients in embryo control this.
• HOX and Homeobox genes in animal
kingdom

28. Morphogenesis
Example of invagination
Cells change shape
Coordinated by position
Role of Cytoskeleton

39. Early Cleavage Differences
• Protostomes
– Spiral cleavage
– Determinate
– Mosaic pattern
– Blastopore  mouth
– Arthropods, mollusks,
annelids
• Deuterostomes
– Radial cleavage
– Indeterminate
– Regulated
development
– Blastopore  anus
– Echinoderms,
chordates

40. Blastula Differences
• Small eggs – symmetrical blastula
(Echinoderms and Mammals)
• Large eggs – asymmetrical blastula
(Amphibians, Reptiles, Birds)
• Animal Pole – active side  ectoderm
• Vegetal Pole – inactive  endoderm

41. Gastrulation in Frog
• Morphogenesis: invagination
• Epiboly and Involution for asymmetrical
eggs
• Triploblastic – three tissue layers
– Ectoderm – outer skin, CNS in vertebrates
– Endoderm – lining of the gut
– Mesoderm – inner organs and tissues
– Coelom – body space in proto- and
Deuterostomes.

45. Notocord in Chordates
• First tissue to fully differentiate
• Forms in mid-dorsal mesoderm
(chordamesoderm)
• Induces formation of neural tube and cranial
space in nearby ectoderm (dorsal side)
• Replaced by spinal column (cartilage and
bone from mesoderm) in vertebrates

51. Differentiation of Mesoderm
• Mid-dorsal – chordamesoderm
• Dorsal – somites – segmented parts of body
• Intermediate – thin layer, contributes to kidney
and/or testicular ducts (labeled “nephrotome” in
previous slide)
• Lateral Plate – two sheets join at mid-ventral line
– Somatic – body side
– Splanchnic – surroundings of gut
– Coelom – body space between two layers of mesoderm

53. Pattern formation
• Studied first in Drosophila
• HOX and Homeobox genes found
throughout animal kingdom
• Frequent repeated inductions followed by
determination, then differentiation
• Stimulates morphogenesis, part of
development

56. Chick
• 3-D slide from dorsal side
• Note:
– Somites,
– Neural tube and cranial space
– Notocord
• Compare to Frog slices

60. CLONING
• Dedifferentiation of carrot cells.
• Demonstration that frog cells are not
terminally differentiated.
• More difficult in mammals!!

63. Summary
• Development is part of a life cycle
• Involves mitosis for nuclear division
• Changes in control of DNA cause
differentiation (different proteins made in
different concentrations)
• Genes and development steps are regulated
by other genes throughout life

65. LIFE CYCLES

66. Reproduction
• To “produce again”
• Life cycle includes both diploid and haploid
phases
• You, as an individual, are the diploid phase
of a life cycle
• Emphasis on phases leads to classification
of life cycles

67. Generalized Life Cycle
Diploid phase
Haploid phase
meiosisFertilization/symgamy
zygote
gametes
Diploid adult??
Haploid adult??

68. Representative Examples
• Chlamydomonas – haplontic (haploid dominant)
life cycle, single celled
• Ulothrix – haplontic life cycle, filamentous
(colony?)
• Ulva – diplohaplontic life cycle, multicellular in
both haploid and diploid phases, phases equal.
• Fern – diplontic (diploid dominant) life cycle
• Animal Kingdom – extreme diplontic life cycle;
learn Echinoderm, Ascaris, human

69. Haploid Phase
Diploid Phase
HAPLONTIC STYLE OF LIFE CYCLE

70. Chlamydomonas
• Protist
• Chloroplast
• Haplontic life cycle (Haploid dominant)
• No mitosis in diploid phase of cycle
• Represents very early Eukaryotic life cycles

71. Chlamydomonas

72. ULOTHRIX
• Haplontic life cycle
• “Multicellular” in haploid phase (colonial?)
• Both growth and asexual reproduction by
mitosis in haploid phase.
• Diploid phase (resting spore) can only
perform meiosis (no mitosis in diploid
phase)

73. New Terms
• Gametophyte – the gamete-producing plant.
This describes a multicellular HAPLOID
phase in plant life cycles. This plant
produces gametes by MITOSIS
(chromosome number stays the same!).
• Spore – a haploid cell that will divide by
mitosis (usually to produce a gametophyte).

74. More New Terms
• Gametangium – in Ulothrix and many
similar algae, it is a specialized cell that
produces gametes by mitosis.
• Sporangium, or zoosporangium – a
specialized cell that produces spores
(zoospores) by mitosis.
• Zoospore – a spore that is flagellated.

75. Diploid phase
Resting spore only
Haploid phase
Includes spores, a multicellular
filament (gametophyte), and gametes
Ulothrix Haplontic style life cycle

76. Alternation of generations
• Ulva is our example
• Introduction of mitosis in the diploid
phase!
• Eons of evolutionary time to develop
• Loss of asexual reproduction in the haploid
phase for some species.
• Mitosis still in haploid phase for growth and
production of gametes.

77. New Terms
• Sporophyte – the spore producing plant.
This is the multicellular DIPLOID plant. It
produces spores by MEIOSIS (chromosome
number reduced from diploid to haploid).
• Sporangium – specialized cells or ORGAN
(multicellular structure) that produces
spores by meiosis. Located on the
sporophyte.

79. Emphasis of Diploid Phase
• Ferns, Conifers, Flowering Plants
• Gametophyte becomes less important in the
life cycle (smaller than sporophyte and with
a shorter lifetime).
• Sporophyte develops complex tissues and
organs.

80. New Terms for Fern
• Thalus – name for the gametophyte (n).
• Archegonium – gametophyte (haploid)
organ that produces eggs by mitosis.
• Antheridium – gametophyte (haploid) organ
that produces sperm by mitosis.
• Sorus – structure on underside of
sporophyte leaf that contains many
sporangia (diploid) that produce spores by
meiosis.

85. Evolutionary Trends
• Shift in emphasis from haploid dominant to
diploid dominant life cycles.
• Shift from haploid to diploid organisms.
• Single to multicellular; increased tissue
differentiation; longer lives
• Emphasis on mitosis for reproduction in haploid
phase (asexual) to use of it for growth, then
growth in diploid phase
• Meiosis/fertilization ONCE per life cycle (sexual
reproduction)

87. SUMMARY
• Switch in emphasis from dominant haploid
to dominant diploid phases.
• Development of multicellularity, then of
tissue differentiation.
• Role of MITOSIS undergoes significant
change.
• Roles of meiosis and fertilization do NOT
change.