Chapter 11- Fish and mammals

1. Chapter 11- Fish and mammals • Large broods • Breed year-round • Easy and cheap • Transparent embryos • Develop outside mother • Early development complete in 24 hours 1 • Zebrafish are becoming the sweetheart of developmental biologists A. Cleavage 6 Three cell populations 1st 12 divisions are sychronous to form _____________ 1. __________ _____ (EL) 2. ____layer- gives rise to embryo proper Blastoderm is perched on a large ________ Fig. 11.1 3. ____________ layer (YSL) Fig. 11.2

2. B. Gastrulation Recall Epiboly from Ch 9 Deep cells migrate to outside then encase entire yolk Epiboly Movement not by crawling, but by YSL cells expansion and pulling EL cells along Embryonic shield epiblast 1. Enveloping layer (EL) hypoblast 2. Deep cells Fig. 11.3 3. YSL cells YSL 6 hrs post-fertilization • A ________ is formed either by _________ of superficial cells or by _______ • These combine with superficial epiblast cells to form the _______________ (function equivalent of the dorsal lip in amphibians)

3. B. Gastrulation (cont.) The hypoblast cells extend in both directions to form the notochord precursor Animal Head Ventral Dorsal Ectoderm Trunk Tail Fig. 11.3 Vegetal Mesoderm Endoderm Fig. 11.2 -A zebrafish fate map

4. C. Axis formation 1. Dorsal ventral axis- As with the amphibian __________ (Organizer), the embryonic shield: • Establishes the _______________ axis • Converts lateral/ventral medoderm to dorsal mesoderm (notochord) • Convert ectoderm to neural rather than epidermal B-catenin samois goosecoid 2. Forms the ______________ precursor BMP inhibitors e.g. Chordino

5. Chordino Embryonic shield C. Axis formation 1. Dorsal ventral axis- As with the amphibian dorsal lip (Organizer), the embryonic shield: • 3. Secretes proteins to inhibit BMP from inducing ectoderm to become epidermis • This inhibiting molecule is called ___________ • If mutate________, no neural tube is formed B-catenin samois Fig. 11.6 goosecoid BMP2 BMP inhibitors e.g. Chordino • 4. Acquires its function from _________ accumulation in nearby cells • B-catenin accumulates in _____ cells • ______________is activated

6. C. Axis formation (cont.) 2. _________________ axis- In amphibians , the anterior-posterior axis is formed during oogenesis This axis is stabilized during gastrulation by _____________ ________________________. _________ neural inducing signal (from ectoderm cells) Fig. 11.6 __________ neural-inducing signal ( from mesoderm cells) 3. ________________ axis - Not much known, but involves ______ family signaling molecules

7. Mammalian Development Tough to study!! • ______ diameter (1/1000th volume of frog egg!) • Few in number ___________ • Develops within mother • Cleavage events take _____ hours each • Development occurs en route to ___________ 3. Cleavage during migration down _________ 2. fertilization 4. Implant in ______ 1. Egg released from _____ Fig. 11.20

8. Amphibians Mammals A. Cleavage Mammalian Development Distinctions of mammalian cleavage • Slow- ______ hrs per cleavage • 2nd cleavage is ______________ • Marked __________ in early cell division • Cleavage at 2nd division requires newly made ________ from zygote Fig. 11.21-rotational cleavage in mammals 5. ____________ (marked cell huddling) occurs at 8 cell stage compaction Fig. 11.23- Compaction at 8 cell stage (______ in humans)

9. A. Cleavage (cont.) 16 cell embryo is termed “_______” • external cells will become___________, which will become the _________ • Internal cells will become_____________ (ICM), or the______________ This marks 1st differentiation event in mammalian development At 64 cell stage, an internal cavity appears and the embryo is termed a ___________, ready for implantation onto uterus wall • The ______________ (recall ch. 7) must be shed in order to implant • Blastocyst ____ a small hole in zona using the enzyme _______ Note- attachment of embryo to oviduct wall is called a ______________.

10. B. Gastrulation Similar to __________ and birds • Mammalian embryo relies on __________ for nutrients, not yolk • Thus, the embryo must have a specialized organ to accept nutrients- called the ___________ • The chorion induces uterine cells to become a _________ (rich in blood vessels) Epiblasts form ______________ epiblasts Hypoblasts (from ICM) line the ________- these give rise to ______________________. hypoblasts blastocoel Fig. 11.28- Day 15 human embryo

11. B. Gastrulation (cont.) Mammalian ______ and ______ cells arise from epiblasts that migrate through primitive streak E-cadherin attachment is mechanism Direction of migration _____________ _____________ Fig. 11.28- Day 16 in human Fig.11.11- Chick gastrulation- similar to mammalian Those cells that migrate through the ____________ will become the _________________.

12. B. Gastrulation (cont.) Extraembryonic membrane Formation Trophoblast cells (originally termed “cytotrophoblast”) gives rise to multinucleated ____________________ Uterine wall • These syncytiotrophoblasts: • secrete proteolytic enzyme to invade __________________ • Digest uterine tissue • Mothers blood vessels contact the syncytiotrophoblast cells • Embryo produces its own blood vessels Fig. 11.27-Blastocyst invading uterus Embryo’s blood vessels Chorion Villi Blood vessels feed embryo, but blood cells do not mix Embryo chorion Mother’s Placenta Fig. 11.31 Mothers blood vessels

13. C. Anterior-posterior axis formation • Two signaling centers • _______________________ (AVE) • _________ (Organizer) These work together to form ___________. Fig. 11.34 These are on opposite sides of a “cup” structure Node produces _____ and ________ Knock-out of one of these results no _________ AVE produces ______ and Otx-1

14. C. Anterior-posterior axis formation The Hox genes specify _________________ polarity These are homologous to _________ gene complex (Hom-C) of __________ Recall that the Hom-C genes are arranged in the same order as their expression pattern on anterior-posterior axis Mammalian counterparts are clustered on_________ ___________ . Equivalent genes (Hoxb-4 and hoxd-4) are called a ____________ _________.

15. C. Anterior-posterior axis formation (cont.) Fig. 11.36- Hox genes are organized in a linear sequences that concurs with posterior to anterior structures This is referred to as the ___________

16. Incus Stapes Hox gene rules 1. Different sets of Hox genes are required for __________ of any region of the _____________________ axis Hoxa-2 KO- _______ missing, duplicate incus Hoxa-3 KO- thymus, ______________ malformed 2. Different members of a paralogous group may specify different ___________ in a given region Hoxd-3 KO = deformed ______ (1st vertebra) Example Hoxa-3/Hoxd-3 _______ KO- atlas and neck cartilage nearly absent 3. A hox gene KO causes defects in the _____________ of that gene’s expression

17. Retinoic Acid has a profound effect on development Recall amphibian development (Ch. 10) Structure of retinoic acid (not in textbook) Fig. 10.41 Hox gene RA Retinoic acid bind a receptor, then the complex binds promoter of a hox gene Retinoic acid activates mammalian _____ genes Retinoic acid is likely produced in the _____, and perhaps more time spent in the node dictates more ___________ specification Lacks all distal vertebra Wild-type mouse embryo RA-treated mouse embryo

18. D. Dorsal-ventral axis formation Dorsal axis forms from ICM cells near _____________ Inner cell mass (ICM) Ventral axis forms from ICM cells near _____________ Trophoblast Blastocoel Fig. 11.32 Fig. 11.42 E. Left-right axis formation Note that mammals are ___________ Two levels of regulation- 1. Global- an ____ gene defect results in all ______ on the wrong side 2. Organ-specific- an ___gene defect causes the axis of an organ to change Organs are located in specific locations