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Developmental Biology. Life Cycles and Developmental Stages. Developmental Stages. Dividing embryogenesis into stages allows for easier description of embryonic events Stages should follow logical, observable changes in the embryo

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developmental biology

Developmental Biology

Life Cycles and Developmental Stages

developmental stages
Developmental Stages
  • Dividing embryogenesis into stages allows for easier description of embryonic events
  • Stages should follow logical, observable changes in the embryo
  • Refinement of classical embryological stages with the advent of molecular technology has occurred
developmental stages3
Early Development

Fertilization

Cleavage

Gastrulation

Neurulation

Later Development

Organogenesis

Larval molts

Metamorphosis

Aging

Developmental Stages
developmental stages4
Early Development

Fertilization

Cleavage

Gastrulation

Neurulation

Later Development

Organogenesis

Larval molts

Metamorphosis

Aging

Attraction of sperm to egg

species specificity

attraction at a distance

Fusion of sperm and egg

activation of egg to complete meiosis

prevention of polyspermy

Fusion of pronuclei

Rearrangement of cortical cytoplasm

Developmental Stages
developmental stages5
Early Development

Fertilization

Cleavage

Gastrulation

Neurulation

Later Development

Organogenesis

Larval molts

Metamorphosis

Aging

Rapid cell divisions

Drosophila 8’, Xenopus 20’

no transcription

S and M phases only

mammals 12-24 hr, chick 6-12 hr

transcription occurs

Produces a hollow embryo

blastocoel

mesoderm induction

signals from endoderm induce ectodermal cells

Developmental Stages
developmental stages6
Formation of gut

Complex cell movements to arrange trilaminar embryo and set up body plan

Major movements are of the mesodermal cells

Positioning of mesodermal cells to interior of embryo

Early Development

Fertilization

Cleavage

Gastrulation

Neurulation

Later Development

Organogenesis

Larval molts

Metamorphosis

Aging

Developmental Stages
developmental stages7
Cell movements occur in distinct ways in different genera

Invertebrates

invagination of cells on the future ventral side

Vertebrates

fish & amphibians

spherical embryos

involution of mesoderm on future dorsal side at blastopore lip

Early Development

Fertilization

Cleavage

Gastrulation

Neurulation

Later Development

Organogenesis

Larval molts

Metamorphosis

Aging

Developmental Stages
developmental stages8
Vertebrates

Reptiles, birds and some mammals (humans)

disc embryos

delamination of ectoderm to form endoderm & mesoderm

delaminating cells involute at Henson’s node, primitive streak and groove form & progresses along dorsal midline

mammals (mouse)

cup embryos

ingression at the dorsal midline (primitive streak) as in chick and human

Early Development

Fertilization

Cleavage

Gastrulation

Neurulation

Later Development

Organogenesis

Larval molts

Metamorphosis

Aging

Developmental Stages
developmental stages9
Invertebrates

Echinoderms

unusual CNS

Arthropods

form CNS from region from neural cells that are displaced from the neuroectoderm

Early Development

Fertilization

Cleavage

Gastrulation

Neurulation

Later Development

Organogenesis

Larval molts

Metamorphosis

Aging

Developmental Stages
developmental stages10
Vertebrates

Dorsal ectoderm is induced by the notochord to become neural tissue

Ectoderm turned into neural tissue is called the neural plate

Neural plate cells change shape & fold into neural tube

Early Development

Fertilization

Cleavage

Gastrulation

Neurulation

Later Development

Organogenesis

Larval molts

Metamorphosis

Aging

Developmental Stages
developmental stages11
neural crest

transition zone between neural plate & ectoderm becomes neural crest

crest cells leave dorsal neural tube & migrate throughout embryo differentiating into multiple cell types

melanocytes – pigment cells

peripheral nervous system – sensory and motor nerves

adrenal gland

Early Development

Fertilization

Cleavage

Gastrulation

Neurulation

Later Development

Organogenesis

Larval molts

Metamorphosis

Aging

Developmental Stages
developmental stages12
Invertebrates

Highly variable depending on phyla

Arthropods (insects)

Imaginal discs

Specialization of segments

Developmental Stages
  • Early Development
    • Fertilization
    • Cleavage
    • Gastrulation
    • Neurulation
  • Later Development
    • Organogenesis
    • Larval molts
    • Metamorphosis
    • Aging
developmental stages13
Vertebrates

Complete body plan is apparent at end of neurogenesis

Pharyngula

All vertebrate embryos similar appearance

Major landmarks

branchial arches/visceral arches/pharyngeal pouches

segmented neural tube

segmented axial mesoderm – somites

Early Development

Fertilization

Cleavage

Gastrulation

Neurulation

Later Development

Organogenesis

Larval molts

Metamorphosis

Aging

Developmental Stages
developmental stages14
Forming organs

gut tube, proctodeum (anus), stomodeum (mouth)

pronephros (kidney)

dorsal aortas

heart

liver diverticulum

eye anlagen

otic vesicles (ears/tympanic membranes)

cartilage deposition

Early Development

Fertilization

Cleavage

Gastrulation

Neurulation

Later Development

Organogenesis

Larval molts

Metamorphosis

Aging

Developmental Stages
developmental stages15
Invertebrates

Arthropods and Nematodes

Series of larval stages

Several orders of magnitude increases in organismal size

Ecdysysis – shedding of exoskeleton/epiderm

Holometabolous arthropods

Imaginal discs

Precursor to adult organ

Hormonally induces to develop during larval stages

Early Development

Fertilization

Cleavage

Gastrulation

Neurulation

Later Development

Organogenesis

Larval molts

Metamorphosis

Aging

Developmental Stages
developmental stages16
Arthropods

Evagination of imaginal tissues

Echinoderms

Massive revision of body plan

Chordates

Tunicates

Loss of chordate structures

Cephalochordates

Amphibians

Major changes to respiratory system & digestive tract

Early Development

Fertilization

Cleavage

Gastrulation

Neurulation

Later Development

Organogenesis

Larval molts

Metamorphosis

Aging

Developmental Stages
developmental stages17
Cell senescence

Regeneration

Early Development

Fertilization

Cleavage

Gastrulation

Neurulation

Later Development

Organogenesis

Larval molts

Metamorphosis

Aging

Developmental Stages
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