Bio 102 Exam 3

Cadherins

major family of cell adhesion molecules (CAMs), mediate calcium-dependent cell-cell interactions

Catenins

anchor cadherins to the actin cytoskeleton

Ransick and Davidson "trick"

Added micromeres to embryo bathed in Ca2+ free seawater, embryos began to dissociate

Ascidians

Tunicates/sea squirts, from the phylum chordata with vertebrates, contains notochord, color-coded cytoplasm

Notochord

rodlike structure supporting chordates, contains fluid filled vacuoles, in tunicates, the notochord is lost during development

Unfertilized tunicate egg- description of cytoplasm

Clear cytoplasm/ectoplasm at animal pole, central gray cytoplasm, yellow cytoplasm (cortical layer with lipids) associated with vegetal pole plasma membrane

Tunicate egg 5 minutes after sperm entry

Clear ectoplasm extends, yellow cytoplasm/myoplasm extends, sperm pronucleus forms in yellow cytoplasm

Sperm pronucleus migrates from vegetal pole to equator

Gray cytoplasm at animal half, yellow cytoplasm/myoplasm at vegetal half, sperm pronucleus migrates equator, which is where ectoplasm is located

Final step before cleavage

Ectoplasm fills entire animal half, yellow cytoplasm forms yellow crescent, two gray cytoplasm- chordoplasm (light to dark gray) and gray cytoplasm (light gray)

Myoplasm

yellow cytoplasm, region with muscle determinants

Conklin

Created fate map of ascidians, ablating cells containing mypolasm causes no muscle to form

Nishida

Injected yellow cytoplasm into tunicate cells that don't typically form muscle: lead to muscle formation

Nishida and Sawada

Used tunicate Halocynthia roretzi and macho-1 transcription factor:

Exp 1: used probe to detect macho-1 mRNA, when it was present, muscle cells formed

Exp 2: inhibited translation of macho-1 mRNA, no macho-1 protein, no muscle formation, larval tails were shortened

Exp 3: Injected macho-1 into cells that do not form muscle (gray cytoplasm), this caused muscle formation

Nishida and Sawada important details

-Autonomous specification: certain determinants exist in the egg cytoplasm

-morphogenetic determinants (transcription factors) impact gene expression

-spacial distribution of determinants is crucial

Hopeful mutation

mutation that can potentially assist in survival and reproduction in the future

Drisophila Oogenesis

cytoplasmic connections between the egg and nurse cells, nurse cells provide the bulk of the cytoplasmic contents to the mature oocyte. As the egg cell grows, the nurse cells degenerate, and the egg fills the egg chamber right before the egg is laid

Nurse cells

somatic cells from the mother that serve to provision the egg

Internal fertilization

male and female mate, female lays effuse around 50-70 per day

Superficial cleavage

Cleavage in drosophila, nuclear divisions without cytokinesis (multinucleate), nuclei move to the periphery of the developing embryo

9th nuclear division

about 4/5 nuclei migrate to the posterior pole, and become surrounded/encased by the cell membrane, generating pole cells, which gives rise to germ cells

Formation of blastoderm

Cell membrane encloses the nuclei

Gastrulation

Formation of 3 cell layers: ectoderm, mesoderm, endoderm. Formation of 14 body segments

Imaginal cells

undifferentiated cells in newly hatched larva

imaginal disks

clusters of imaginal/undifferentiated cells, local thickening- cells will receive signals to differentiate, becoming eyes, wings, etc.

Segmentation

AP polarity of embryo, larva, and adult is determined by origin in the anterior-posterior polarity of the egg

Maternal effect genes

genes in mother that produces mRNAS located in various regions in the egg, these mRNAs encode transcription factors and translational regulatory proteins, which diffuse to activate and repress certain genes: proteins are morphogens, regulate expression of segmentation

Morphogens

soluble molecules capable of diffusion, effects are concentration dependent, morphogens can specify more than one cell fate by forming a concentration gradient

Source

location where morphogen is produced, typically the highest concentration- morphogen will diffuse away, causing a decrease in concentration

Wolpert French Flag Model

multi potential cells, meaning they can become anything based on morphogen concentration- blue, white, and red regions are all on based on concentatration

Gene regulatory networks

gene can cause activation of other genes, linked interactions

Bicoid

encodes morphogen, transcribed in nurse cells, bicoid mRNA moves to egg cytoplasm through cytoplasmic bridges, bicoid mRNA is localized in the anterior region, tethered to the cytoskeleton

Bicoid mRNA

5' UTR and 3' UTR around coding region, after egg is laid, bicoid mRNA is translated, the protein is made, and it diffuses

Bicoid experiments

Exp 1: "bicoid -": transplanted bicoid nMRNA from WT into anterior region of bcd- mutant (normal development)

Exp 2: "bcd-": inject bicoid mRNA from WT into middle of mutant (head formation in middle)

Exp 3: "bicoid mRNA from WT" injected into posterior region of WT (head on both sides)

Segmentation genes

gap genes, pair rule genes, segment polarity genes

Gap genes

gap proteins function in dividing the embryo into broad regions, control expression of pair rule genes

pair rule genes

proteins refine segment locations, subdivide the broad "gap" regions into parasegments (ex hairy, runt)

Segment polarity genes

proteins determine boundaries and A-P organization of the segments

Homeotic genes

proteins that determine the role of each segment, development (hom/hox genes), regional identity, found in all animals, encode transcription factors, genes have a region of DNA called a homeobox, which becomes a hom/hox protein with a homeodomain, genes are often clustered on a chromosome

Organization of hom/hox genes

specific order, position of gene on chromosome is correlated with the expression pattern along the body axis- if a gene is located more towards the 3' end of cluster of genes, then the anterior limit of expression is more anterior (and vice versa)= collinearity/spacial collinearity

How did hom/hox cluster evolve?

gene duplication events, or duplication of hom/hox gene clusters

Cohn and Tickle

Examined pythons, which evolved from tetrapod lizards. Lizards have forelimbs and hindlimb, pythons only have rudimentary hindlimbs- genes involved are Hox B5, Hox C8, and Hox C6. Chicks vs pythons- in chicks, Hox C6 and C8 are expressed along body axis in limb region (between limbs), which allow for both forelimbs and hindlimb. In pythons, the expression domain of C6 and C8 extend along the body axis, to the neck region. When C6 and C8 are extended to neck region, there is complete elimination of forelimbs

Kruppel protein

regulation of expression of kruppel gene, protein is expressed in center of embryo- MEMORIZE HANDOUT

Loss of repression

causes expansion of border

loss of activator

causes constriction of border

How can hunchback both activate and repress Kruppel gene expression?

depends on concentration. At low concentration, hunchback activated Kruppel, but at high concentration, hunchback represses Kruppel

Enhancers

A site where transcription factors bind. A gene may have multiple enhancers, and repressors and activators both use enhancers. More than one transcription factor can bind to more than one enhancer

Variation in enhancers

enhancers differ in their number/affinity

- concentration of transcription factor

- affinity of transcription factor for enhancer

- strength of activator or repressor

Low concentration of hunchback

activation of kruppel gene expression (hunchback has high affinity for activator enhancer)- if TF has a high affinity for an enhancer, need low concentration of TF for binding- central region contains low concentration

high concentration of hunchback

repression of kruppel gene expression (hunchback has low affinity for repressor enhancer)- if TF has a low affinity for an enhancer, need high concentration of TF for binding, anterior contains high concentration

Erwin- cambrian explosion

540 million years ago. O2 and aerobic respiration allowed organisms to become larger and more complex, with gene regulatory networks

Plant and Animal similarities

Sexual reproduction, single-cell embryo, and development of multicellular organism

Differences between plants and animals

life cycle of plants has an alternation of generations (haploid/diploid). Plants have little cellular movement during development. Plant seed contains the embryonic plant (lacks major organs of mature plant, meaning no early archenteron)

Animal development

Multicellular organism (2N), undergoes meiosis, forms 1N gamete, two gametes fuse during fertilization to form a 2N zygote, mitosis occurs and organism develops

Plant development

Multicellular organism/sporophyte (2N), undergoes meiosis, forms 1N spores, mitosis occurs (1N multicellular organism- gametophyte), gametophyte produces 1N gamete, two gametes fuse during fertilization to form a 2N zygote, mitosis occurs- 2N sporophyte

haplodiplontic

alternation of generations- multicellular haploid and diploid stages (mitosis occurs in both stages) - embryonic development only occurs in diploid stage

Angiosperm

Flowering plant

Gametophyte

highly reduced, gives rise to gamete, depends on sporophyte for survival

Carpel

middle of flower, produces the female gametophyte

stamen

the male reproductive organ of a flower, gives rise to male gametophyte, contains an anther and a filament

tepals

found in alstroemeria, petals and sepals with similar structures

Pollen grain

pollen grain contains a vegetative cell, which contains a nucleus and a generative cell inside. The generative cell produces sperm, and the vegetative cell forms a pollen tube

generative cell

Usually lacks mitochondria and chloroplasts. Separated from vegetative cell by a very thin wall, or possibly only by a plasma membrane. As generative cell develops, it becomes completely surrounded by the vegetative cell cytoplasm. After "germination" of pollen grain, generative cell undergoes 1 cell division, and produces 2 sperm cells. One sperm (1N) fertilizes the egg, and the other (1N) joins with the female polar nuclei to create the endosperm

what happens to male microspore mother cells?

2N, one undergoes meiosis, producing 4 haploid microspores. each becomes a pollen grain, and each will undergo a mitotic division, causing each pollen grain to have two cells (vegetative and generative)

Production of female gametophytes

Ovules in cartel give rise to egg. outer ovule layer develops into seed coat. Inside embryos there is an egg (1N), 3 antipodal cells (1N), a central cell with 2 nuclei (2N), and 2 synergies (1N)- 7 cells, 8 nuclei

endosperm

when one sperm joins with polar nuclei of central cell (3N) triploid- endosperm provides nutrition for the embryo

what happens to the female mother megaspore?

2N megaspore undergoes meiosis to become 4 haploid (1N) daughter cells. Only one survives, undergoes 3 rounds of mitosis. 7 cells are produced (one cell in mitosis #2 undergoes replication but no cytokinesis). This 2N cell becomes the central cell

pollination

refers to landing and subsequent germination of the pollen grain on stigma. Pollen takes up water, the pollen tube grows and extends down the style to ovule. Growing pollen tube contains actin and filament supports the anther. Pollen tube enters synergies. vesicles originating from Golgi (dictyosomes) fuse to membrane and dump contents. 2 sperm discharged into the synergid, one sperm goes to the central cell (b/c of cytoplasmic bridges), fuses with the egg cell (2N zygote), other sperm goes to central cell, fuses with the polar nuclei (2) -> triploid endosperm

embryogenesis in plants

development of embryo from the time of fertilization to formation of seed

post embryogenesis

development from time of germination of the seed to the formation of the mature plant (sporophyte, 2N), most of tissue development occurs during this phase, involves the activity of meristems.

Meristems

Meristems are clusters/populations of undifferentiated cells (like stem cells in vertebrates)

Primary meristems

shoot and root meristems (set up shoot and root axis, polarity) formed during embryogenesis (vegetative meristems)

Secondary meristems

meristems that form during post embryonic development, includes the floral meristems, produces floral organs (ex. petal, carpel), vegetative meristems can also be secondary (in some plants, vegetative meristems can be secondary and convert into floral meristems)

Inflorescence meristems

in some plants, vegetative meristems transformed into inflorescence meristems, which produce bracts and floral meristems

How are flowers formed?

Change in identity of vegetative meristems, gene expression, gene regulatory networks

ABC model in arabadopsis

Three classes of genes (ABC), these genes function as "transcription factors"

Gene classes

Class A: Apetala 2 (AP2), Apetala 1 (AP1)

Class B: Apetala 3 (AP3), Postillata (PI)

Class C: Alamos (AG)

Combos:

A is sepal (whorl 1)

A + B is petal (whorl 2)

B + C is stamen (whorl 3)

C is carpel (whorl 4)

"Revised" model

ABC model, but also includes sepellata, or SEP, which is found in whorl 2,3,4, or B, B+C, and C, when SEP is delayed (Sep-), flowers only have sepals (A), no petals, stamen, or carpels

Quartet model

Gene products, which are transcription factors, associate with each other and form tetrameric complexes- they come together and function in activating/repressing gene expression- complexes act together as transcription factor, entire quartet is needed in order to get proper function

Floral organ identity genes

part of a larger gene family, MADS box genes (similar to homeobox in hom/hox genes)- MADS box has 174-180 base pairs, and is transcribed and translated into a 58-60 amino acid protein.

Evolution of MADS box genes

Found in plants that do not form flowers, must also be involved in other functions. Occurred in common ancestor of angiosperms, gymnosperms, ferns, and moss (angiosperms are the only ones with flowers), gene duplication events resulted in the presence of multiple MADS box genes- angiosperms have sepals, petals, stamen, and carpel- gymnosperms only have sex organs (st and ca)

Plants vs. animals

developmental mechanisms evolved independently, different genes involved in gene cascades

Similarities: gene cascades/regulatory networks, gene duplications

Animal hom/hox genes exhibit collinearity. Plants MADS box genes are sequestered throughout chromosomes, not clustered