Development

Tool-kit genes are conserved genes that encode proteins that function very similarly to regulate development across many species. Which of the following genes could be a tool-kit gene?

Hox (homeotic) genes

Where are stem cells found?

In early human embryos or the bone marrow of adults

Pluripotency

In embryonic stem cells, the property of being undifferentiated, with the capacity to form every type of cell in an organism form any cell in body) the ability of a cell (called a pluriopent cell) to form any cell of the body.

what evidence is there that Differentiated Animal Cells Are Genetically Equivalent (frog cell nuclei, wilmut adult sheep, dolly, cell differences result from _________)

Nuclei from differentiated frog cells transferred to enucleated frog eggs can yield tadpoles Wilmut et al. fused adult sheep cells with enucleated eggs and implanted them into surrogate mothers: A cloned lamb (named Dolly) was born Dolly was a genetically identical copy of the donor adult sheep Thus, adult cells are genetically equivalent; cell differences result from differential gene expression

inderect development

Organism is developed outside of the organism therefore don't appear the same as the parent cell until the end of development. Metamorphosis as it takes to the end of development to transform and appear like a parent organism.

combinatorial control

Regulation of a biological outcome, for example differentiation of a particuar cell type, that is acheived by the use of a specific combination of regulators, not just one regulator specific for the outcome. - allows the use of a smaller set of regulators to achieve many outcomes, such as different specialized cell types, in contrast to the use of single master regulators specific to each particualar cell type

In situ hybridization (ISH) (what is it, used for what, how does it work)

Technique used to locate cells that manufacture a specific protein or peptide by detecting the specific mRNA sequence coding for that substance. It can also be used to study changes in regional mRNA levels (i.e., gene expression). detect DNA,mRNA, and gene expression) technique for detecting specific DNAs and mRNAs in cells and tissues by use of labeled complementary probes. Can be used to determine where and when particular genes are expressed in embryos. works by adding lavel to single stranded DNA or RNA molecule to create probe, complementry in sequence to mRNA of interest in an embryo or any other biological specimen

differential gene expression

The expression of different sets of genes by cells with the same genome.

What makes cells different?

- differential gene expression - cell signaling

Oocyte establishes body axis of adult which is an

An elongated cell that already contains positional information, even before fertilization

Anterior/Posterior axis in Drosophila Based on opposing gradients of two different proteins produced by nurse cell mRNAs:________ (anterior) and Nanos (posterior) 2 other maternal messages, hunchback and caudal, are evenly distributed across the egg what is bicoid and nanos

Bicoid Bicoid inhibits translation of caudal mRNA Nanos inhibits translation of hunchback mRNA

cell movement and expansion

Cells can move past one another within a block of animal cells, causing drastic shape changes in the embryo. Cells can break away from a block of animal cells and migrate to new locations. Plant cells can regulate the plane of cell division and expand in specific directions, causing dramatic changes in shape.

A gene can be regulated at multiple levels: (5)

Chromatin condensation Transcriptional control Alternative splicing and selective destruction of mRNAs Translation rate Activation and deactivation of proteins

what specialized properties do cells acquire during differentiation(distanct cells have ______ because of what)

Distinct cell types have different structures and functions This is because they contain different molecules

differential gene expression

Expression of different sets of genes in cells with the same genome. Responsible for creating different cell types.

homeotic genes

Genes that determine basic features of where a body part is. Order of homeotic genes along chromosome corresponds to their expression along the A-P axis

conclusions derived from gurdon's experminent

In terms of genetic potential, an intestinal epithelial cells is equivalent to a 1 cell embryo (the fertilized egg)

Fertilization

Process in sexual reproduction in which male and female reproductive cells join to form a new cell - haploid cells join to form a diploid embryo

Homologous

Similarity among organisms of different species due to shared ancestry. Features that exhibit such similarity (e.g., DNA sequences, proteins, body parts) are said to be homologous. Compare with homoplasy. See homology.

somatic nuclear transfer

The nucleus of a fully differentiated cell is transferred into an enucleated egg (ovum). The nucleus can undergo reprogramming to initiate animal development and give rise to all of the cells of a mature organism.

Genome

all of an organism's genetic material

Phenotypic diversity has resulted not from large changes in genes but from

changing patterns of expression

germ layers

ectoderm, mesoderm, endoderm

Like all insects, segments organized into three body regions:

head, thorax, and abdomen

Ectoderm

outermost germ layer; produces sense organs, nerves, and outer layer of skin

self-renewal

process of cell division in which a cell divides to produce one copy of itself and another cell that specializes into a different cell type; usually used in the context of stem cell self-renewal.

Transcriptome

the complete complement of RNA produced by a cell or organism

Weintraub looked for ______ factors that dicted, "become a muscle cell" - what did they convert into what and attached a ____ promoter - they found what

transcription factor that dictates, "become a muscle cell:" They converted myoblast m R N A s into c D N A s and attached a "general" promoter They found a c D N A that could convert many cell types into muscle-like cells

Homeotic genes encode homeotic proteins that function as

transcription factors

cell fate

ultimate morphological features that a cell or group of cells will adopt

embryonic stem cells

undifferentiated cells that are unlike any specific adult cell embryo differentaite into adult cell type) cell from an early animal embryo that has the potential to differentiate into any cell type found in the adult.

stem cells

unspecialized cells that retain the ability to become a wide variety of specialized cells any relatively undifferentiated cell that can divide to produce a daughter cell that remains a stem cell and a daughter cell that can differentiate into specific cell types. Divide to produce a cell that remains a stem cell and one that differentiates Stem cells are found in stem cell niches: These cells divide to meet the needs of the embryo or adult

segmentation genes (what do they determine) and process)

Genes that determine the number and polarity of body segments. 1. Maternal effect genes activate the gap genes 2. Gap proteins expressed in broad bands in the embryo 3. Gap gene and maternal effect gene products function as transcription factors to activate the pair-rule genes in alternating stripes in the embryo 4. Once the pair-rule genes are activated, their gene products then regulate the segment-polarity genes 5. Expression pattern of a segment-polarity gene corresponds to portions of segments in the adult fly

what are two central organizing principles?

Genetic regulatory cascades and the evolutionary conservation of key developmental genes are general features of development During development, the same regulatory genes and signaling molecules are often used over and over in a variety of contexts.

Stem cells act as tissue-resident reservoirs of undifferentiated cells which have the capacity for _______________ (_____ division) and _____cells can differentiate into several cell types

-Capacity for self-renewal (asymmetric division) -Daughter cells can differentiate into several cell types

Essential Developmental Processes (common to all developmental processes in every multicellular organism:) (5)

1. Cell Proliferation - cells divide by mitosis and cytokinesis; timing, location, and amount of cell division regulated 2. Cell -cell interactions: - signaling - where they are, what they are becoming; signals that are produced by cells influence their neighbors to divide, die, move or differentiate 3. Cell differentiation - Begin to express certain genes rather than others - undifferentiated cells specialize at specific times and places in a stepwise fashion 4. Cells Movement and Expression (move, expand, or contract in certain directions) - cells move past one another within a block of aminal cells, causing drastic shape changes in embryo - cells can break away from a block of animal cells and migrate to new locations - plant cells can regulate the plane of cell division and expand in specidic directions, causing dramatic changes in shape 5. Programmed cell death - timing, location, amount of cell death are regulated

what changes inside a cell commit it to follow a particular pathway of development (3)

1. Central role for epigenetic changes 2. Signals in the embryo induce events that alter chromatin condensation patterns that control which genes can be expressed 3. Gene expression patterns for a particular cell type are set, locking the cell into determination epigenetic changes - Embryo signals induce cascade of events altering chromatin condensation - in turn control gene expression - cell locked into determined state

Stages of Development

1. Fertilization - Haploid cells join to form a diploid embryo 2. Cleavage - mitotic divisions dividing the giant cytoplasm into smaller cells 3. Gastrulation - cells move and reposition to form the 3 germ layers 4. Organogenesis - cells from different germ layers move and interact to form organs

3 kinds of segmentation genes

1. Gap genes Gap mutant - several adjacent segments are missing 2. Pair-rule genes Pair-rule mutant - alternating segments or parts of segments deleted Segment-polarity genes 3. Segment-polarity mutant - anterior or posterior halves of segments are missing, and adjacent regions mirror each other

hierarchy of transcription factors regulates development

1. TF determine formation of body axes and control expression of TF in phase 2 2. TF cause embryo to become subdivided into regions that have properties of indivudal segments. which control Phase 3 3. TF cause each segment and groups of segments to develop specific characteristics control phase 4 4. cells differentiate into specific cell types (skin, nerve, muscle)

what is the molecular basis of determination? (3, and regulation of what is critical for what)

Genome: the complete genetic makeup of an organism Transcriptome: the complete complement of RNA produced by a cell or organism Proteome: the complete complement of proteins that a cell or organism can make Each cell is genetically identical - so regulation of gene expression (which and how much of each protein is produced) is critical for developmental order and process!

positional information in limb development: (4 steps)

1. cell division promotes limb growth 2. cells migrate causing cells to reach correct location 3. cell differentation produces speciallized cells (ex. muscle cells) 4. apoptosis eleminates cells inbetween fingers

cascade conctrolling early drosophila development involes the folowing genes and gene products. (6)

1. maternal effect genes: - (define anterior-posterior) morphogens encoded by maternal effect genes, such as bicoid, define the anterior - posterior axis of early embryo 2. Gap genes (mark large subdivision along anterior-posterior) Gap gene products, expressed under the control of maternal-effect morphogens, mark out large, coarse subdivisions along the anterior-posterior axis. 3. Pair-rule genes (bad correspond to body segment formation) Pair-rule genes are expressed next, primarily in response to gap gene products. Pair-rule genes are expressed in alternating bands. Each band roughly corresponds to a body segment that is forming along the embryo. 4. Segment polarity genes (turn segment polarity genes to define front, middle and rear subregions) Pair-rule genes turn on segment polarity genes that are expressed in a portion of each segment. Segment polarity gene products define front, middle, and rear subregions within the segments laid down by the pair-rule genes. 5. Hox genes (specify adult structure development) Even though body segments have been established, the unique identity of each segment has not yet been specified. Hox genes, which are activated by gene products at many different levels of the regulatory cascade, specify what type of adult structure will develop from each segment in the mature organism. 6. Effector genes (get development done ex: cell division, death, moving, signaling) Expression of effector genes is activated by Hox gene products working with segment polarity and pair-rule gene products. All the genes upstream of effector genes in the cascade are involved in regulation. They are managers In contrast, the effector genes are like workers that actually get the job of development done by executing processes such as cell proliferation, cell movement, cell-cell interactions, programmed cell death (see Table 21.1), and ultimately differentiation.

causes of cell determination (3 and what are they)

1. secreted factor (diffusion of inducers from one cell to another, paracrine factors)) 2. interacting with ECM ( matrix of 1 cell induces change in another cell) 3. cell- cell contact (contact (arrows) between the inducing and responding cells)

homeodomain

A conserved sequence of 60 amino acids used in the binding to DNA. Usually found in transcription factors, it is used to express genes that are related, more specifically in development to make tissues associated with one another.

maternal effect genes

A gene that, when mutant in the mother, results in a mutant phenotype in the offspring, regardless of the genotype. - (define anterior-posterior) morphogens encoded by maternal effect genes, such as bicoid, define the anterior - posterior axis of early embryo

tool-kit genes

A set of key developmental genes that establishes the body plan of animals and plants; present at the origin of the multicellular lineages and elaborated upon over evolutionary time by a process of duplication and divergence. Includes Hox genes.

homeotic/Hox genes:(what are they, found in animal or plant and what else, how are they expressed, how do transcription factors achieve effects by, how do hox genes get their unique identity)

Also known as homeobox genes, they are responsible for differentiating the specific segments of the body, such as the head, tail, and limbs, during embryological development. class of genes found in most animal phyla, including vertebrates, that are expressed in a distinctive pattern along body axes in development and control formation of specific structures. Hox genes code for transcription factors with a DNA-binding sequence called a homeobox. products: transcription factors achieve effects by activating expression of effector genes leading to protein production that create differentiated cells contains conserved DNA sequence (homeobox) codes for DNA binding domain of hox encoded transcription factors Particular combinations of transcription factors encoded by Hox genes give each segment its unique identity or, in the case of homeotic mutations, the wrong identity.

cell adhesion molecules (CAMs) (type of contact, found where, aid in what, positioning of a cell within a mutliceullar ogransim is infloued by what)

Cell to cell contact conveys positional information -proteins found on surface of most cells -aid in binding the cell to the extracellular matrix or to other cells Each animal cell makes its own cell adhesion molecules (CAMs) Positioning of a cell within a multicellular organism is strongly influenced by the combination of contacts it makes with other cells and the extracellular matrix

Waddington's epigenetic landscape

Cells go through several stages of commitment stages before they reach their final differentiated state. Developmental paths are symbolized by a ball rolling down a valley. As the valleys become deeper and narrower, development is constrained (or canalized) into one particular path. Cell fate decisions are made via epigenetics that turn different genes on and off. The epigenetic profiles of differentiated cells are the sum of all epigenetic marks it has received in its lifetime.

Gastrulation

Cells move and reposition to form the 3 germ layers The process by which a blastula develops into a gastrula with the formation of three embryonic layers

epigenetic inheritance

The transmission of a heritable pattern of gene expression from one cell to its progeny that does not involve altering the nucleotide sequence of the DNA. Any pattern of inheritance involving differences in phenotype that are not due to differences in the nucleotide sequence of genes.

Homeobox (HOX) genes, purpose?

Tx regulators, blueprints for skeletal morphology.

master regulator

a gene product that can unleash a series of events that produce a specialized cell type, tissue, or body structure used in development of both animal and plants

direct development

a kind of growth in which an organism gets larger but doesn't go through other changes

bicoid (what type of factor, it binds to what 2 things so what kind of structure can form, how do cell learn their positions, high levels of bicord reslts in what, high concentration anterior or posterior)

a maternal effect gene that codes for a protein responsible for specifying the anterior end in Drosophila melanogaster - regulatory transcription factor - bicoid protein binds to enhancers in DNA and activates genes required for formation of anterior structures - in effect, cells learn their poisition along much of the anterior posterior axis, through the concentration of bicoid - high levels of bicoid result in higher levels of transcription of genes with bicoid bidningsites - high concentrations: anterior - low concentrations or mutations causing absent: Posterior

Stem cells in animals found (place, replace what, create what/help do what)

a variety of locations: May replace skin, blood, and gut cells that die Repair wounds Create a supply of disease-fighting cells

regulatory transcription factors

bind to enhancers, silencers, and promoter-proximal elements, and are responsible for the expression of particular genes in particular cell types and at particular stages of development - influence the assembly of the basal transcription complex

how is the fate of a cell specified meaning what does it depend on (3)

by signals arising inside the cell (cytoplasmic determinants) or outside the cell (induction): timing (current stage of deleopment of organism) spatial location where it is in the body of organism

Gurdon Experiment

cell differentiation due to changes in gene expression not gene loss -Discovered that the nuclei of differentiated cells could be reprogrammed to become pluripotent removed the nucleus of a fertilized egg cell from a frog and replaced it with the nucleus of a cell taken from a tadpole's intestine. This modified egg cell grew into a new frog, proving that the mature cell still contained the genetic information needed to form all types of cells.

determined (what is it, what happens if cell is determined, what happens when cell is not determined)

cell is locked into a certain path Cells are moved to a new location within a developing embryo to learn if they are determined: If the cell is determined, it will continue on its normal path If it is not determined, it can take on a new fate irrevocable (under normal conditions) commitment of an embryonic cell to a particular pathway of differentiation.

Organogenesis

cells from different germ layers move and interact to form organs organ formation that takes place during the first two months of prenatal development

De-differentiation

cells grow in reverse, process by which cells become less specialized and return to an earlier cell state within the same lineage. This suggests an increase in a cell potency, meaning that after dedifferentiation, cells may possess an ability to redifferentiate into more cell types than it did before. The process of reversing the normal course of cell specialization (differentiation). Can be induced to create induced pluripotent stem cells (iPS cells).

Many molecules that work in pattern formation exist in a (______, high conctrations near what)

concentration gradient, with high concentrations near the source of the molecule and lower concentrations farther away.

genetically equivalent

contain the same genes When all different cell types of a multicellular individual possess the same genome.

Ultimate targets of Hox gene function must be genes that

control cell behaviors associated with organ morphogenesis

Which is most important in differentiation?

control of transcription via chromatin condensation. Genes in condensed regions of chromatin are not transcribed while genes in regions of relaxed chromatin have the possibility of being transcribed. Regulating how tightly chromatin is packaged is an essential element of differential gene expression. Differences in the patterns of chromatin condensation are the basis of epigenetic inheritance, any form of inheritance that is not based on nucleotide sequence differences in alleles (Ch. 19, Section 19.2).

induces pluripotent stem cells (IPS)

differentiating to form specialized cell type by culture control) An undifferentiated cell made in experimental settings by the de-differentiation of a specialized adult cell. Induced pluripotent cells have the potential to form any cell of the body if re-differentiated under appropriate conditions. cells destroyed by diesease could be replaces with patients own ips cells (diabetes, parkinson, heart desres)

segment (what is it, and drosphila have how many segments, how many are heads, thoracic, abdomnial segments)

distinct region of an animal body that contains a distinct set of structures and is repeated along its length. In the fruit fly and other animals, segmentation genes organize cells and tissues into distinct segments A Drosophila embryo has 15 segments: 3 head, 3 thoracic and 9 abdominal segments Each will give rise to unique morphological features in adult (ex: mouthparts, wings, legs)

pair rule genes

divide embryo into units of two segments each expressed in alternating stripes, each stripe of protein found in portion of ever other segment. proteins encoded by pair-rule genes regulate segment polarity genes (band correspond to body segment formation) Pair-rule genes are expressed next, primarily in response to gap gene products. Pair-rule genes are expressed in alternating bands. Each band roughly corresponds to a body segment that is forming along the embryo.

segment polarity genes

establish anterior-posterior gradient within each segment (turn segment polarity genes to define front, middle and rear subregions) Pair-rule genes turn on segment polarity genes that are expressed in a portion of each segment. Segment polarity gene products define front, middle, and rear subregions within the segments laid down by the pair-rule genes. this stage all segments of the body are defined

Weintraub work worked with: embryonic cells "MYOBLASTS" determined to be muscle cells despite looked nothing like muscle cells hypothesis: EXPERIMENT SETUP: results

hypothesis: myoblast express at least 1 crucial transcription factor that can trigger their differentiation to muscle cells isolate mRNA's from myoblast convert mRNA's: to cDNAs using reverse transcriptase because myoblast predicted to transcribe genes that control muscle - cell differentiation - reasoned that cDNA's must include copies of key transcipts attach "general promoters": to cDNA's insure expression of cDNA in any tupe of cell (general promoter) Introduce cDNA's: into non-mucle cells(finroblasts) monitored development of cells result master regulator present of muscle cell differentiation one of myoblast derived cDNA converted fibroblasts into muscle-like cells

Homeotic mutations:

lead to the wrong body part forming in the wrong place

stem cell niches

location in organism where stem cell population are found unique environments to keep stem cell undifferentiated state and control their division to meet needs of embryo or adult

Yamanaka and colleges work (what did they look are reprogramming, when introduced it expressed what, what was eventually found, results)

looked at reprogramming skin cells into type of stem cells found in early embryo (embryonic stem cells) form any cell in body (pluripotency) introduced/expressed different combinations of genes that encode transcription factors active in early development eventually found 4 combination transcription factors that cause differentiated adults cells to de-differentiate to an embryonic stem cell like state. results: IPS cells

explain how pattern formation is progressive:

major elements in body are set ip by morphogens genes activated by morphogens signal other genes to generate signal molecules providing specific info to parts of body development continues new signals arrive, activate genes specify finer and finer regions within embro, development unfolds in a cascade of events unleashed by a few key initial signals

Mesoderm

middle germ layer; develops into muscles, and much of the circulatory, reproductive, and excretory systems

cleavage

mitotic divisions dividing the giant cytoplasm into smaller cells. zygot diveds in many smaller peaces called blastomers that clustor and form a BLASTULA

cell proliferation

process of increasing cell numbers by mitotic division = cells divide by mitosis and cytokinesis; timing, location, and amount of cell division regulated

gap gene expression

produce broad bands of proteins that act as TF to activate pair-rule genes, these TF bind to enhancers that are located adjacent to pair-rule genes (mark large subdivision along anterior-posterior) Gap gene products, expressed under the control of maternal-effect morphogens, mark out large, coarse subdivisions along the anterior-posterior axis.

morphogens

proteins whose concentration gradients can specify different cell fates A substance that provides positional information in the form of a concentration gradient along an embryonic axis. (cells detect different concentrations providing spatial information) molecule that exists in a concentration gradient and provides spatial information to embryonic cells. give positional information and promote cellular change concentration dependent manner with critical threshold concentration distributed asymmetrically in oocyte or egg precursor embryo by secretion and transport

What controls how a tool kit gene works?

regulatory sequences of DNA. Mutation of these sequences allows conserved tool-kit genes to achieve different outcomes in different species.

Homeosis

replacement of one body part with another (changes proper limb formation and location)

evo-devo

research field of evolutionary-developmental biology Focuses on understanding how changes in developmentally important genes have led to the evolution of new phenotypes

In embryo, key process is creation of a

segmented body plan

cell-cell interactions

signals that are produced by cells influence their neighbors to divide, differentiate, move, expand, or die

why is construction of oocyte critical for first developmental stages

specialized nurse cells move maternal mRNAs into oocyte determine initial developmental course

Meristems (what are they, present in what 2 things, produce what)

stem cells in plants Present in embryos and adults Produce plant structures throughout a plant's life

myoblasts

stem cells that fuse to form each muscle fiber undifferentiated cells in the embryo that are determined to become muscle cells

Proteome

the entire set of proteins expressed by a given cell or group of cells

maternal effect mutations

the genotype of the mother (not zygote) is critical and determines the associated phenotype. Maternal effect genes usually code for RNA or protein that is deposited into the egg by the mother. mutation in a mother that alters the phenotype of her offspring without causing an obvious mutant phenotype in the mother. Is explained by altered cytoplasmic determinants that control embryonic development that are placed in the egg by the mother.

Endoderm

the inner germ layer that develops into the lining of the digestive and respiratory systems

cell differentiation

the process by which a cell becomes specialized for a specific structure or function usually by changes in gene expression =Begin to express certain genes rather than others - undifferentiated cells specialize at specific times and places in a stepwise fashion

Programmed cell death (apoptosis)

timing, location, and amount of cell death are regulated

commitment (when does it occur, how does it work like, what happens over time)

when an embryonic animal cell becomes dedicated to a cell specialization path This occurs gradually, initially weak and reversible occurs when an embryonic animal cell becomes dedicated to follow a particular path of cell specialization. Commitment doesn't work like an on-off switch; rather, cells become committed gradually. Initially, commitment is weak and can easily be reversed. Over time, a cell becomes more and more deeply committed until—under normal conditions—the path it follows does not change.