Ch 47 Fertilization through organogenesis Animal Development Ch 47 Fertilization through organogenesis

Stages of Human Development Fertilization Zona pellucida First cell division Cleavage Blastomere Holoblastic cleavage Meroblastic cleavage regulation Morophogenesis Gastrulation Organogenesis

Fertilization Female secretions increase sperm motility and change structure to cause fertilization potential (capacitation) Moist environment necessary for sperm First six hours

Fertilization Zona pellucida contain receptor cite and acrosomal reaction which binds sperm to egg Changes cause slow polyspermy to prevent additional sperm from entering egg No fast polyspermy reactions in mammals

Zona pellucida Follicle cell Sperm nucleus Cortical granules Figure 47.5 Zona pellucida Follicle cell Figure 47.5 Fertilization in mammals. Sperm nucleus Cortical granules Sperm basal body

Fertilization First Cell Division Mitosis forms true nuclei in daughter cells 12-36 hours after sperm bonding Each cell is now a blastomere http://www.hhmi.org/biointeractive/human-embryonic-HHMI embryonic development

Cleavage Rapid cell division with almost continuous S and M phases of cell cycle Little or no protein synthesis (G1 or G2) Blastula- Hollow ball of cells form with blastocoel cavity

(a) Fertilized egg (b) Four-cell stage (c) Early blastula Figure 47.6 50 m (a) Fertilized egg (b) Four-cell stage (c) Early blastula (d) Later blastula Figure 47.6 Cleavage in an echinoderm embryo.

Cleavage In frogs and mammals is holoblastic “holo” means complete Humans have 3 divisions in first three days with little yolk forming Birds and reptiles cleavage is meroblastic (incomplete) to get extensive yolk formation The “ends” of the blastula are called the animal pole and vegetal pole Gray crescent is the area on the opposite side from sperm binding

8-cell stage (viewed from the animal pole) Figure 47.7 Zygote 2-cell stage forming Gray crescent 0.25 mm 8-cell stage (viewed from the animal pole) 4-cell stage forming Animal pole 8-cell stage Figure 47.7 Cleavage in a frog embryo. 0.25 mm Blastula (at least 128 cells) Vegetal pole Blastocoel Blastula (cross section)

Regulation of Cleavage The total mass of the structure does not change from zygote to blastula, the cells just get smaller Cells divide until the ratio of material in each nucleus to cytoplasm is sufficiently large Small cells balance the amount of DNA to mRNA for protein synthesis (think surface are to volume ratio)

Morphogenesis Transformation of embryo orientation and shape Important is the cell shape, position and survival Two important phases: Gastrulation- establishment of cell layers Organogenesis- formation of organs

Morphogenesis: Gastrulation During gastrulation there is a mass movement of cells which results in the blastula becoming a gastrula Three germ layers develop ectoderm- outside layer mesoderm- middle layer endoderm- inside layer Some organisms (cniderians) do not have a mesoderm HHMI Differentiation and Cell Fate http://www.hhmi.org/biointeractive/differentiation-and-fate- cells

ECTODERM (outer layer of embryo) Figure 47.8 ECTODERM (outer layer of embryo) • Epidermis of skin and its derivatives (including sweat glands, hair follicles) • Nervous and sensory systems • Pituitary gland, adrenal medulla • Jaws and teeth • Germ cells MESODERM (middle layer of embryo) • Skeletal and muscular systems • Circulatory and lymphatic systems • Excretory and reproductive systems (except germ cells) • Dermis of skin • Adrenal cortex Figure 47.8 Major derivatives of the three embryonic germ layers in vertebrates. ENDODERM (inner layer of embryo) • Epithelial lining of digestive tract and associated organs (liver, pancreas) • Epithelial lining of respiratory, excretory, and reproductive tracts and ducts • Thymus, thyroid, and parathyroid glands

Gastrulation in Sea Urchin Figure 47.9 Animal pole Blastocoel Mesenchyme cells Gastrulation in Sea Urchin Vegetal plate Vegetal pole Blastocoel Filopodia Mesenchyme cells Archenteron Blastopore Figure 47.9 Gastrulation in a sea urchin embryo. 50 m Blastocoel Ectoderm Archenteron Key Blastopore Mouth Future ectoderm Mesenchyme (mesoderm forms future skeleton) Digestive tube (endoderm) Future mesoderm Anus (from blastopore) Future endoderm

Gastrulation in Frog SURFACE VIEW CROSS SECTION Animal pole 1 Figure 47.10 SURFACE VIEW CROSS SECTION Animal pole 1 Blastocoel Gastrulation in Frog Dorsal lip of blasto- pore Dorsal lip of blastopore Blastopore Early gastrula Vegetal pole 2 Blastocoel shrinking Archenteron Figure 47.10 Gastrulation in a frog embryo. Ectoderm 3 Blastocoel remnant Mesoderm Endoderm Key Future ectoderm Blastopore Future mesoderm Late gastrula Yolk plug Archenteron Blastopore Future endoderm

Migrating cells (mesoderm) Endoderm Hypoblast Figure 47.11 Fertilized egg Primitive streak Gastrulation in Chick Embryo Yolk Primitive streak Epiblast Future ectoderm Figure 47.11 Gastrulation in a chick embryo. Blastocoel Migrating cells (mesoderm) Endoderm Hypoblast YOLK

Gastrulation in Human Figure 47.12 Blastocyst reaches uterus. Endometrial epithelium (uterine lining) Gastrulation in Human Inner cell mass Uterus Trophoblast Blastocoel 2 Blastocyst implants (7 days after fertilization). Expanding region of trophoblast Maternal blood vessel Epiblast Hypoblast Trophoblast Expanding region of trophoblast 3 Extraembryonic membranes start to form (10–11 days), and gastrulation begins (13 days). Amniotic cavity Epiblast Hypoblast Yolk sac (from hypoblast) Extraembryonic mesoderm cells (from epiblast) Figure 47.12 Four stages in the early embryonic development of a human. Chorion (from trophoblast) 4 Gastrulation has produced a three-layered embryo with four extraembryonic membranes. Amnion Chorion Ectoderm Mesoderm Endoderm Yolk sac Extraembryonic mesoderm Allantois

Morphogenesis: Gastrulation in Humans 1. Blastocyst first 6 days Fertilization occurs in the oviduct Inner cell mass becomes the embryo which is the source for stem cells Little yolk (stored nutrients) Inner cell mass Blastocyst reaches uterus.

Morphogenesis: Gastrulation in Humans 2. Trophoblast 7 days after fertilization Outer epithelium secretes enzymes for implantation which allows for blood to surround trophoblast Epiblast-upper layer becomes the embryo Hypoblast- lower layer Maternal blood vessel

Morphogenesis: Gastrulation in Humans 3. Extraembryonic membranes 10-11 days Formed by embryo Enclose special structures outside the embryo Gastrulation begins day 13 when implantation is complete Cell migration occurs as cells move inward from epiblast through primitive streak to form mesoderm and endoderm Chick gastrulation

Expanding region of trophoblast Figure 47.12c Expanding region of trophoblast Amniotic cavity Epiblast Hypoblast Yolk sac (from hypoblast) Extraembryonic mesoderm cells (from epiblast) Chorion (from trophoblast) Figure 47.12 Four stages in the early embryonic development of a human. 3 Extraembryonic membranes start to form (10–11 days), and gastrulation begins (13 days).

Morphogenesis: Gastrulation in Humans 4. End of gastrulation Three germ layers are formed Extraembryonic layers from placenta These layers are an evolutionary necessity in land (dry) environments

Extraembryonic mesoderm Figure 47.12d Amnion Chorion Ectoderm Mesoderm Endoderm Yolk sac Extraembryonic mesoderm Allantois Figure 47.12 Four stages in the early embryonic development of a human. 4 Gastrulation has produced a three-layered embryo with four extraembryonic membranes.

Organogenesis Research brain intestine Spinal cord liver More localized changes Research brain intestine Spinal cord liver Bones (or specific) Muscles (or specific) skin eyes heart ears HHMI