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

Fig B. Gastrulation Epiboly Deep cells migrate to outside then encase entire yolk Movement not by crawling, but by YSL cells expansion and pulling EL cells along 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) 1. Enveloping layer (EL) 2. Deep cells 3. YSL cells hypoblast epiblast Embryonic shield 6 hrs post-fertilization YSL Recall Epiboly from Ch 9

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

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

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

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

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

Mammalian Development 1.Slow- ______ hrs per cleavage 2.2nd cleavage is ______________ 3.Marked __________ in early cell division 4.Cleavage at 2 nd division requires newly made ________ from zygote Distinctions of mammalian cleavage Fig rotational cleavage in mammals Fig Compaction at 8 cell stage (______ in humans) compaction 5. ____________ (marked cell huddling) occurs at 8 cell stage A. Cleavage AmphibiansMammals

16 cell embryo is termed “_______” external cells will become ___________, which will become the _________ Internal cells will become _____________ (ICM), or the ______________ A. Cleavage (cont.) This marks 1 st 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 ______________.

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) B. Gastrulation Fig Day 15 human embryo Hypoblasts (from ICM) line the ________- these give rise to ______________________. Epiblasts form ______________ blastocoel hypoblasts epiblasts

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

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

C. Anterior-posterior axis formation Two signaling centers 1._______________________ (AVE) 2. _________ (Organizer) Fig These are on opposite sides of a “cup” structure These work together to form ___________. Node produces _____ and ________ AVE produces ______ and Otx-1 Knock-out of one of these results no _________

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 ____________ _________. C. Anterior-posterior axis formation

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

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

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

D. Dorsal-ventral axis formation Inner cell mass (ICM) Dorsal axis forms from ICM cells near _____________ Ventral axis forms from ICM cells near _____________ Blastocoel Fig Trophoblast E. Left-right axis formation Note that mammals are ___________ Fig 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