Embryology
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Transcript of Embryology
EMBRIOLOGIA&
CICLO CELULAR
JUAN CARLOS MUNEVAR
APPLICATIONS OF MITOSIS AND MEIOSIS
A Characteristic of Living things
Growth, Division, Reproduction
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
APOPTOSIS
EVOLTUION OF EMBRYOS
•Requires multicellularity
•Only becomes embryology when cells are differentiated.
•Follows a common pattern in the Animal Kingdom
Stages in Embryology
Animal Examples
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
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)
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
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
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)
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
Morphogenesis
Example of invagination
Cells change shape
Coordinated by position
Role of Cytoskeleton
Early Cleavage Differences
• Protostomes
– Spiral cleavage
– Determinate
– Mosaic pattern
– Blastopore mouth
– Arthropods, mollusks, annelids
• Deuterostomes
– Radial cleavage
– Indeterminate
– Regulated development
– Blastopore anus
– Echinoderms, chordates
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
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.
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
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
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
Chick
• 3-D slide from dorsal side
• Note: – Somites, – Neural tube and cranial space– Notocord
• Compare to Frog slices
CLONING
• Dedifferentiation of carrot cells.
• Demonstration that frog cells are not terminally differentiated.
• More difficult in mammals!!
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
LIFE CYCLES
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
Generalized Life Cycle
Diploid phase
Haploid phase
meiosisFertilization/symgamy
zygote
gametes
Diploid adult??
Haploid adult??
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
Haploid Phase
Diploid Phase
HAPLONTIC STYLE OF LIFE CYCLE
Chlamydomonas
• Protist
• Chloroplast
• Haplontic life cycle (Haploid dominant)
• No mitosis in diploid phase of cycle
• Represents very early Eukaryotic life cycles
Chlamydomonas
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)
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).
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.
Diploid phase
Resting spore only
Haploid phase
Includes spores, a multicellular filament (gametophyte), and gametes
Ulothrix Haplontic style life cycle
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.
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.
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.
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.
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)
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.