Animal Development

1. AnimalDevelopment Let me out!

2. Fertilization!

3. Fertilization • Joining of sperm & egg • sperm head enters egg

4. Blocking polyspermy • Triggers opening of Na+ channels in egg cell membrane • depolarizes membrane • “fast block” to polyspermy • Triggers signal transduction pathway • release of Ca+2 from ER causes cascade reaction across egg • “fertilization envelope” forms • like bubble around egg • “slow block” to polyspermy

6. “Fast block” to polyspermy • Release of Na+causes depolarization wave reaction across egg membrane

7. Human fetal development • Day 1: 1st cleavage • 1 cell becomes 2 (2-cell stage) • Day 2: 2nd cleavage • 4-cell stage • Day 3: 6-12 cell stage • can test at this stage for genetic diseases if done by IVF • Day 4: 16-32 cell stage • solid ball of cells = morula

8. Cleavage • Repeated mitotic divisions of zygote • 1st step to becoming multicellular • unequal divisions establishes body plan • different cells receive different portions of egg cytoplasm & therefore different regulatory signals

9. Cell signaling • Regulating the expression of genes that affect the developmental fate of the cell

10. Cleavage • zygote  morula  blastula • establishes future development

12. Ovulation to implantation

13. Human fetal development • Day 5: • solid morula develops into hollow, fluid-filled blastula • embryo will develop from the inner cell mass, or embryonic disc • Day 6 -7: • blastocyst attaches to the endometrium (uterine lining) & burrows in: implantation • blastocyst starts to secrete HCG = human chorionic gonatotropin • stimulates estrogen & progesterone to prevent menstrual flow • causes "morning sickness" in some women... • pregnancy test measures the amount of this hormone!

14. Embryonic Development link 1.A series of cell divisions. Zygote becomes morula which a. occurs in b. leads to the hollow ball Cleavage mitotic oviduct blastula Gastrula 2. One side of blastula indented. Differentiate 3. 3 embryonic layers specialize. ectoderm • Outside • Middle • Inside • Increase is mesoderm endoderm growth

15. Embryonic Development : 1. Cleavage: repeating mitosis forms a hollow ball of cells, no increase in size, just in cell number! 2. Blastula: A hollow ball of cells approximately the same size as the zygote (fertilized egg) 3. Gastrulation: One side of the blastula indents. 4. Differentiation: see next slide!

16. Differentiation Ectoderm: The outer part of the gastrula becomes the nervous system and epidermisof the skin. Mesoderm: The middle of the gastrula becomes the muscles, skeleton, circulatory system, excretory system and reproductive system. Endoderm: The inner layer becomes the lining of the digestive tract, respiratory tract and the liver and pancreas.

17. Gastrulation blastopore:forms at sperm penetration point archenteron:forms endodermembryonic gut mesoderm dorsal lip: organizing center for development tissue formation

18. Human fetal developmental • Days 10 - 14: • pregnancy becomes established • fluid filled amniotic cavity starts to form • yolk sac starts to form • will make blood cells, germ cells • embryo starts to form from embryonic disc • chorion (placenta) starts to form • At the end of this stage, a woman will have just missed her period! Day 14

19. Morphogenesis • organization of differentiated cells into tissues & organs • cell migration • by changes in shape • cells fold inward as pockets by changing shape • cell movements • cells move by pseudopods projecting from the cell body • signals from cues • guided by following chemical gradients • respond to adhesive cues from recognition proteins on adjacent cells

20. Human fetal developmental • Days 15 - 21: • emergence of the vertebrate body plan • primitive streak starts to form • the site of gastrulation (formation of 3 tissue layers = ecto, endo, and mesoderm) • neural groove begins to form • future spinal cord & brain • somites begin to form • bands of tissue that will become muscles & bones • pharyngeal arches begin to form • future face, neck, mouth, nose

21. Vertebrate body plan Day 19

22. Organogenesis Umbilical blood vessels Mammalian embryo Chorion Bird embryo Amnion Yolk sac Allantois Fetal blood vessels Placenta Maternal blood vessels

23. Organ development • Organ development begins with the formation of: • neural tube • future spinal cord & brain • notochord • primitive skeleton, replaced by vertebrate spinal column • somites • bands of tissue that will become muscles & bones

24. Coelom • Acoelomates • flatworms • Pseudocoelomates • roundworms, nematodes • Coelomates • mollusca, annelida, arthropoda, echinodermata, & chordata

25. Sex determination Zygote Sperm Develop in early embryo Y Testes XY Ovum X SRY Seminiferous tubules Indifferent gonads Leydig cells No SRY X Ovaries Ovum XX (Follicles do not develop until third trimester) X Sperm Zygote

26. Master control genes • Homeotic genes • master regulatory genes • in flies these genes identify body segments & then turn on other appropriate genes to control further development of those body sections • Example: SRY gene

27. Homeotic genes • Mutations to homeotic genes produce flies with such strange traits as legs growing from the head in place of antennae. • structures characteristic of a particular part of the animal arise in wrong place antennapedia flies

28. Homeobox DNA • Master control genes evolved early • Conserved for hundreds of millions of years • Homologous homeobox genes in fruit flies & vertebrates • kept their chromosomal arrangement link

29. Homeotic genes, also known as Hox genes specify the anterior-posterior axis and segment identity of metazoan organisms during early embryonic development. These genes are critical for the proper number and placement of embryonic segment structures (such as legs, antennae, and eyes). Malformation of the HOX gene? Return of the Indian Goddess of Valor? Roman god-Janus, guarder of the gates Diprosous: Craniofacial duplication

30. Evolutionary Constraints on Development • Basic body plans of the major animal groups have not changed due to a limited number of homeotic genes (master genes) • These genes have imposed limits • taxonomic / evolutionary • physical • architectural

31. Placenta • Materials exchange across membranes

32. Human embryonic developmental • Week 3 - Week 8 = embryo • development of all organ systems • Day 22: the heart begins to beat Day 24 Day 28Week 4

33. Human embryonic development • embryo showing tail & limb buds

34. Human embryonic development • beginning of the eye can be seen, as well the bulging heart & the umbilical cord

35. Human embryonic development • lens of the eye can be seen forming, the mass of the heart bulging from the chest, & the beginnings of the finger rays

36. Human embryonic development

37. Human embryonic development • beginning of the ear is clearly seen note the bend of the elbow joint has begun, the fingers are forming and toes are beginning to bud off the foot

38. Human fetal development 4 weeks 7 weeks

39. Apoptosis • Programmed cell death • Sculpts body parts • Genetically programmed elimination of tissues & cells that were used for only short periods in embryo or adult • human embryos develop with webs between toes & fingers, but they are not born that way!

40. Apoptosis

41. Human embryonic development • Note the formation of the nose, eyelids, ear flap & well defined toes & fingers 50–60 days (8 weeks) Both knee & elbow are visible. Embryo has formed most of basic organ systems & will spend remainder of development in “fetal” period. Organs grow, mature, & begin to learn their respective functions

42. Human fetal development • Day 52: • first brain waves can be detected • weeks 4-8 is when all major organ systems of body are formed & when most teratogens have greatest effect Week 8

43. Human fetal development Week 10

44. Human fetal development • At 15 weeks the embryo begins to take on more of a typical baby's form & the attachment of umbilical cord can be clearly seen Week 15

45. Human fetal development • Week 9 - week 40 = fetus • after 12 weeks or so, the baby's development is largely "finished" • some exceptions: brain & lung development Week 16

46. Human fetal development 12 weeks 20 weeks

47. Human fetal development • The fetus just spends much of the 2nd & 3rd trimesters just growing …and doing various flip-turns & kicks inside amniotic fluid Week 20

48. Human fetal development • 24 weeks (6 months) fetus is covered with fine, downy hair called lanugo. It’s skin is protected by a waxy substance called vernix

49. Human fetal development • 30 weeks (7.5 months) umbilical cord

50. Human fetal development • 32 weeks The fetus sleeps 90-95% of the day & sometimes experiences REM sleep, an indication of dreaming