Lecture 25 Animal Development

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cytoplasmic determinant

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A regulatory transcription factor or signaling molecule that is distributed unevenly in the cytoplasm of the egg cells of many animals and that directs early pattern formation in an embryo.

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acrosomal reaction

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A set of events occurring in a sperm cell upon encountering an egg cell, including release of acrosomal enzymes and formation of the acrosomal process, which helps the sperm cell reach the egg.

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Why is cross fertilization rare

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During sea urchin feritization, species-specific bindin molecules on sperm interact with species-specific fertilizin receptors on the surface of the egg. This interaction is required for the plasma membrane of perm and egg to fuse. As a result cross-species fertilization is rare.

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polyspermy

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Fertilization of an egg by multiple sperm.

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zona pellucida

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The gelatinous layer around a mammalian egg cell. In other vertebrates, called the vitelline envelope.

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cleavage

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In animal development, the series of rapid mitotic cell divisions, with little cell growth, that produces successively smaller cells and transforms a zygote into a multicellular blastula, or blastocyst in mammals.

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embryogenesis

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The process by which a single-celled zygote becomes a multicellular embryo.

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blastomere

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A small cell created by cleavage divisions in early animal embryos.

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blastula

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In vertebrate development, a hollow ball of cells (blastomere cells) that is formed by cleavage of a zygote and immediately undergoes gastrulation.

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what is a key point about cleavage:

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Certain parts of the egg cytoplasm end up in certain blastomeres.

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Radial clevage

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cells divide at right angles to each other.

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spiral clevage

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cells divide at oblique angles to each other

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Discoidal cleavage

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A disk of cells forms on top of a large cell containing the yolk.

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Superficial clevage

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Mitosis is not immediately followed by cytokinesis, resulting in a multinucleate embryo.

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22.3 check understanding

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During cleavage, the egg cytoplasm is divided

*Because certain regulatory signals and transcription factors are found at specific locations in the egg cytoplasm of most species, different blastomeres end up with different sets of cytoplasmic determinants

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gastrulation

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The process by which some cells on the outside of a young embryo move to the interior of the embryo, resulting in the three distinct germ layers (endoderm, mesoderm, and ectoderm).

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germ layer

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In animals, one of the three basic types of tissue formed during gastrulation; gives rise to all other tissues.

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ectoderm

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The outermost of the three basic cell layers in most animal embryos; gives rise to the outer covering and nervous system.

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mesoderm

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The middle of the three basic cell layers in most animal embryos; gives rise to muscles, bones, blood, and some internal organs (kidney, spleen, etc.)

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endoderm

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The innermost of the three basic cell layers in most animal embryos; gives rise to the digestive tract and organs that connect to it (liver, lungs, etc.).

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blastocoel

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Fluid-filled cavity in the blastula of many animal species.

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blastopore

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A small opening (pore) in the surface of an early vertebrate embryo, through which cells move during gastrulation.

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organogenesis

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A stage of embryonic development, just after gastrulation in vertebrate embryos, during which major organs develop from the three embryonic germ layers.

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notochord

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A long, gelatinous, supportive rod down the back of a chordate embryo, below the developing spinal cord. Replaced by vertebrae in most adult vertebrates. A defining feature of chordates.

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neural tube

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A folded tube of ectoderm that forms along the dorsal side of a young vertebrate embryo and that will give rise to the brain and spinal cord.

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somites

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Paired blocks of mesoderm on both sides of the developing spinal cord in a vertebrate embryo. Give rise to muscle tissue, vertebrae, ribs, limbs, etc.

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determination

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In embryogenesis, progressive changes in a cell that commit it to a particular cell fate. Once a cell is fully determined, it can differentiate only into a particular cell type (e.g., liver cell, brain cell).

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trace the development of a muscle cell

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Start with egg inside your mother. After fertilization triggered the onset of clevage, certain cells in the blastocyst began producing signals that triggered regulatory gene cascades-changes in gene expression that led specific cells to become mesoderm in your back. During gastrulation, these cells move into postion. Early in organogenesis, signals from notochord and nearby cells induced the production of MyoD and other muscle-determining proteins in certain populations of cells in from somites. In response, these target cells were committed to becoming muscle and moved into your upper arm as it formed. Later, MyoD containin cells began experssing muscle-specific proteins.

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Rational or trancendental Morphologist

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The rational morphologists worked to determine hierarchical patterns in nature. An archetype would be valuable because it would be at the top of said hierarchy. From a religious perspective, this helps reveal a pattern in God’s designs which would be valuable to the rational morphologists. Rational morphologists did not believe in evolution, and thus were not thinking in terms of “common ancestry”.

The goal of rational morphologist was to reduce the observed diversity of organisms to a more general level of abstraction-- the archetype.

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what are four archetype of cuvier

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vertebrata
radiata(cnidaria, echinodermss)
Mollusca( snails octapus, worms)
Articulata( arthropods, annelids)

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What did Geoffry try to do?

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He tried to come up with a common archetype for the four archetype( vertebrata, articulata, radiata, Mollusca) that Cuvier came up with.

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What relationship did Geoffry make between the articulata and the vertebrata?

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Veterbrata was just an articulata flipped upside down.

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What relationship did geoggry make between the vetebrata and the Mollusca.

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That the vetebrata resembled the Mollusca when you bend it upward.

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evolutionary morphology(1865-present)

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the goal of the evolutionary morphologist is to reconstruct the evolutionary history and the characters of their common ancestors.

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homeotic mutation:

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Mutation that produces a product or structure of similar structure or function.

antnnapedia, bithorax, extra or sacral vetebrae in mouse.

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Homeotic genes/ Hox genes

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encode transcription factors, which play an important role in giving a unique identity to each segment and thereby setting up morphogenesis along the anterior posterior axis.They are recognizable by the presence of a 60 amino acid long DNA binding region called the homeodomain,but all homeo domain containing proteins are not hox genes.Hox genes exhibit some important properties like

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Orthologous genes:

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same genes found in different organisms

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-Paralogous genes:

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same genes found in organisms of the same type.

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homeodomain

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hox genes have homeobox which encodes for a homeodomain(protein) which regulates transcription of specific developmental genes and thereby determines the fate of cells during development.

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spatial colinearity

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the order of Hox genes along a chromosome is correlated with the location of their expression along the anterior-posterior axis of the embryo.

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Temporal Colinearity

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The order of Hox genes along a chromosome is correlated with the temporal sequence of their expression in the embryo.

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chordin

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establishes dorsal-ventral axis of body

segementation-engralled
appendages-distal-less
Muscle-MEF2, MyoD
Eye: Pax6, eyeless

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Pax6 and others

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establishes light eye receptors

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Planula

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The planula is an ovoid gastrula with a blastopore at one end. You should be able to distinguish between the outer ciliated ectoderm and the inner endoderm.

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hourglass of evolutionary diversity

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we have great diversity in the earliest stages of development, in the blastula and gastrula and neurula, but that they all converge on a more similar form, the pharyngula, at what's called the phylotypic stage…and then they diverge once again to achieve the diversity of adult forms

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pharyngula

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the pharyngula is a stage in embryonic development.[1] Named by William Ballard,[2] the pharyngula stage follows the blastula, gastrula and neurula stages. At the pharyngula stage, all vertebrate embryos show remarkable similarities,[3] containing the following features:

* notochord
* dorsal hollow nerve cord
* post-anal tail, and
* a series of paired branchial grooves.

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Segmented Germ band stage:

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Is an embroyinic stage in arthropods where they display the most amount of similarities.

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Holoblastic cleavage

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involves complete division of the blastomeres (this is what you are familiar with when comparing radial and spiral cleavage).

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Meroblastic cleavage

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involves unbalanced divisions, leaving a substantially larger yolk and smaller cells dependent on the

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different animal groups and their corresponding types of cleavage

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*insects- superficial meroblastic clevage
*many fish,reptiles, birds- discoidal meroblastic cleavage
Most deuterstomes-radial holoblastic clevage.
Most protostomes- spiral holoblasticc cleavage

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Nanos and Caudal

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are maternal effect genes that are important in the formation of more posterior abdominal segments of the Drosophila embryo.

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Bicoid and hunchback

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are the maternal effect genes that are most important for patterning of anterior parts (head and thorax) of the Drosophila embryo.

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Maternal effect/ genes

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The building-blocks of anterior-posterior axis patterning in Drosophila are laid out during egg formation (oogenesis), well before the egg is fertilized and deposited. The developing egg (oocyte) is polarized by differentially localized mRNA molecules.
The genes that code for these mRNAs, called maternal effect genes, encode for proteins that get translated upon fertilization to establish concentration gradients that span the egg

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epiboly

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spreading of an epithelial sheet ot cover deeper cells and tissues

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invagination

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infolding of a region of cells

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involution

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inward movement of an expanding movement of an expanding outer layer.

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ingression

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inward migration of individual cells

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Elamination

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splitting of one cell sheet into two or more parallel sheets.

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Induction

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: an interaction between an inducing and a responding tissue that alters the path of differentiation of the responding tissue

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Competence

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cell or tissue which can adopt a particular fate in an appropriate environment, even if it doesn’t normally