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Cellular and Developmental Biology

by: Miss Maximo Barrows

Cellular and Developmental Biology BIOL 205

Marketplace > University of North Carolina - Chapel Hill > Biology > BIOL 205 > Cellular and Developmental Biology
Miss Maximo Barrows
GPA 3.57

Jason Reed

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Jason Reed
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This 12 page Class Notes was uploaded by Miss Maximo Barrows on Sunday October 25, 2015. The Class Notes belongs to BIOL 205 at University of North Carolina - Chapel Hill taught by Jason Reed in Fall. Since its upload, it has received 17 views. For similar materials see /class/228830/biol-205-university-of-north-carolina-chapel-hill in Biology at University of North Carolina - Chapel Hill.


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Date Created: 10/25/15
problem set G W hand in answer in recitations 48 a On the following diagram of an antibody molecule indicate i a heavy chain ii a light chain iii the sites that bind antigen b How many genes are required to make a single antibody molecule c What gene segments make up an antibody heavy chain gene d Which gene segments encode the part of the antibody that binds antigen 49 Brie y describe the genetic changes that occur in a developing B cell before it sees an antigen Include allelic exclusion as part of your answer 50 a Which B cells respond to an infection by a substance not previously seen b Which B cells respond to a second infection one year later by the same foreign substance c What is the difference between the responding cells in part a and the responding cells in part b 51 Which of the following types of somatic mutations might increase binding of an antibody to an antigen it recognizes change of one nucleotide in the Cm heavy chain gene segment removal of one nucleotide in a D heavy chain gene segment change of one nucleotide in a V light chain gene segment 52 To produce antibodies against a short peptide one generally attaches the peptide to a larger protein quotcarrierquot and then injects the carrier peptide into a rabbit The rabbit then produces antibodies against both the peptide and the carrier a Do the same B cells produce antibodies against the carrier and against the short peptide b Why is it necessary to use the carrier 53 HIV the virus that causes AIDS recognizes the CD4 protein What cells normally have this protein and why does the virus cause immunodeficiency 54 If a mouse is irradiated with Xrays and then B cells from another mouse are introduced will the resulting mouse defend itself against quotattackquot by a a virus b a kidney from a foreign mouse c a harmless chicken protein injected into the bloodstream Why or why not What if T cells from another mouse are also introduced into the irradiated mouse 55 Name one type of cell that has the following receptors on its surface a CD4 but not CD8 b CD8 but not CD4 c both CD4 and CD8 d MHC class II molecule 56 If a heart is transplanted from one animal to another the recipient39s immune system will reject the transplanted tissue a What cells of the immune system recognize the foreign heart cells b How do these cells distinguish foreign cells from host cells c What happens to the foreign cells d How does the immune system impose this fate on the foreign cells e Why doesn t the immune system reject its own cells leClConverterInputZRc8luLQjZ htm532011 104103 PM Check page 374375 Geneexpression pro ling by DNA microarray Identi cation of all the genes expressed in a particular tissue or at a particular stage of development can be accomplished DNA microarrays DNA chips enables levels of RNA transcripts of thousands of genes to be measured simultaneously and allows to monitor the changes in gene expression that occur within a tissue or embryo at different stages of development or after experimental manipulation Flat surfaces studded with a regular array of clusters or spots39 of DNA fragments of known sequence each cluster representing a DNA sequence found in a speci c protein coding gene DNA fragments are known as probes39 Probes can be made from cDNAs that have been made by reverse transcription of mRNA To determine which genes are being expressed the total mRNA from the tissue of interest is extracted then either ampli ed as RNA or converted into cDNA and ampli ed by the PCR Nucleic acid is tagged with uorescent dye and hybridized to the microarray Microarray is scanned and the ratios of the signals from both dyes at each spot are recorded and converted into a relative expression level for the test sample In order to nd all the genes expressed at particular stages in early development mRNA from multiple embryos at the appropriate stage need to be extracted and labeled and hybridized to miniaturized microarrays Then biding patterns of the labeled RNAs will indicate which genes are expressed at the different stages To achieve growth to such a large size oocyte Mechanism increase the overall number of gene copies in the developing oocyte so that amount of proteins that can be synthesized also increases Factors in the cytoplasm maintain the totipotent potential of the egg Mature gametes undergo a program of differentiation Cell differentiation does not involve any alteration in the sequence or amount of DNa but involves epigenetics changes 0 Epigenetic changes chemical modi cation to DNA and to chromosomal proteins associated with it that change the structure of the chromosome locally so that some genes are selectively silenced while others can still be expressed Liver cells hepatocytes Epigenetic changes associated with that cell type are passed on to the daughter cells so that they are also hepatocytes or w e Unlike differentiated somatic cells mature gametes must retain totipotent potential and in order to do this ability of the cytoplasm of an unfertilized egg to reprogram39 the nucleus from a differentiated somatic cell so that it reverts to a totipotent state and is able to direct the development of a new organism this forms the basis of animal cloning by somatic cell nuclear transfer In mammals some genes controlling embryonic growth are imprinted39 Genomic imprinting certain genes are switched off either the egg or the sperm during their development and remain silenced in the genome of the early embryo and this makes cloning mammals much more dif cult to achieve 0 Two paternal genomes androgenetic abnormal 0 Two maternal genomes gynogenetic abnormal W When mammals are cloned using donor nuclei from differentiated somatic cells these nuclei will not have gone through the normal reprogramming and imprinting process that occurs during germ cell formation and this could account for the large number of failures and abnormalities in the cloned embryos The insulinlike growth factor IGF Z is required for embryonic growth its gene Ig is imprinted in the maternal genome 9that is it is turned off so that only paternal gene is active Only very low levels of IGF 2 are produced from the imprinted maternal gene and that is not enough to make up for the loss of IGF 2 expression from the paternal genome Gene H19 is the opposite of Igf2 Imprinting occurs during germcell differentiation and a mechanism is required both for maintaining the imprinted condition throughout development and for wiping it out during the next cycle of germcell development 0 DNA methylation an epigenetic modi cation in which methyl groups are attached to cytosines in DNA Also associated with gene silencing o Noncoding regulatory RNAs ncRNAs repressor proteins that help package DNA in the chromosomes also involved in imprinting adjacent genes PraderWilli syndrome linked to a loss of expression of the paternal copy of a gene on chromosome 15 usually as a result of a deletion of a small region of the chromosome containing that gene Angelman syndrome also results from the same region Beckwith Wiedemann syndrome due to a generalized disruption of imprinting on a region of chromosome 7 Gem cells specified by germ plasm Drosophila germ plasm specified by oskar at posterior end of egg Celegans germ plasm is characterized by polar granules and PIE1 protein and segregates into P4 during cleavage Xenopus frog germ plasm localized in vegetal region of egg Zebra sh germ plasm in cleavage furrows At the entry of a sperm wave of increased calcium moves across the egg Mechanism is based on activation of phospholipase C Spermderived PLCzeta activates pathway 9 G proteinlinked receptor activates alpha subunit 9 activated phospholipase C 9 cleavage of 1P3 from DAG 9 binding of 1P3 to endoplasmic reticulum and release of Ca2 9Ca activates Anaphase Promoting Complex APC 9 Egg nishes meiosis II 9 Sperm and egg nuclei migrate together to begin the rst mitotic cell cycle Fertilization involves cellsurface interactions between egg and sperm Cumulus cells sticky layer of hyaluronic acid and embedded somatic follicle cells hyaluronidase activity on the surface of the sperm head helps it to penetrate 9zonapellucida a layer of fibrous glycoproteins secreted by the oocyte acrosomal reactionthe release of enzymes contained in the acrosomal vesicle or acrosome located in the sperm head SED1 helps sperm to bind to and penetrate the zonapellucida Changes in the egg envelope at fertilization block polysperm In Xenopus frog an electrical membrane potential across the plasma membrane goes up with a few seconds of sperm entry As the membrane repolarizes an impenetrable membrane called the fertilization membrane is formed around the egg slow block to polyspermy and is triggered by a wave of calcium release in the egg that leads to the cortical granules releasing their contents to the outside of the plasma membrane by exocytosis In mammals only cortical granules are released by exocytosis and their contents for ma layer immediately outside the egg plasma membrane 9 S ermegg fuxlon cauxe a calclum wave mat rexult 1n egg actlvatlon 6 Calclum dielatOr ESTA block actlvatlon 7 y L y m H L a hwh 39 39 p artne r cychn WWW mnemmfnesnmmus CamInkediyd r sgmainn men we mm mm J J comm Ert39ylnioMavs s mam Wmmim Mm mum Immluu ul lklwsl n Ml msli N am mimoan Diplo dmalu y 14VA A kmd PH MPF allowmgthe eggto complete meioxi Hya urumdase acuwaty an smaee m mammahan sperm Sperm penetrates E d H d t mums mg m mg a lane pe um a em 5 a asama reaman m sperm c Enzyme re sassd imm aeraaame sperm head c Sperm p asma membrane fuses mm egg U asma membrane c caxmum waves mmra reatter prawdes b ozk m pa yspermy Sperm nudeus dehvered mm cylup asm Egg camp exes meme and deve opment s mmated 10 Nuclel of dl erentlated cell can Support development 0 H O gt gt wN gt gt mP H Ch H If diploid nuclei from cells at different stages of development replace the nucleus of an egg and support normal development it would indicate that no irreversible changes have occurred to the genome during differentiation It would also show that a particular pattern of nuclear gene activity is determined by whatever transcription factors and other regulatory proteins are being synthesized in cytoplasm of the cell Somatic cell nuclear transfer transplanting nuclei from adult skin kidney heart and lung cells as well as from the intestinal cells into enucleated eggs to support development In general the later the developmental sage the nuclei come from the less likely they are to be able to support development Transplantation of nuclei taken from blastula cells is much more successful by transplanting nuclei from the same blastula into several enucleated egg an even greater success rate is achieved if the process is repeated with nuclei from the blastula stage of a cloned embryo Results show that the genes required for development are not irreversibly altered successful rate of cloning by somatic cell nuclear transfer in mammals is extremely low Patterns of gene activity in differentiated cells can be changed by cell fusion MyoD gene initiate muscle differentiation The differentiated state of a cell can change by transdifferentiation Transdifferentiation the change of one differentiated cell type into another Transdetermination the allied phenomenon in which there is a switch of committed but not yet differentiated progenitor cells into a different lineage Vertebrate life cycles and outlines of development Vertebral column segmented backbone surrounding the spinal cord Anteroposterior axis main body axis of vertebrates Dorsoventral axis running from the back to the belly with the spinal cord running along the dorsal side and the mouth de ning the ventral side 0 Neural tube is the earliest appearance of the nervous system Ectoderm gives rise to the nervous system and epidermis Mesoderm gives rise to the skeleton muscle heart blood and some other internal organs and tissues Endoderm gives rise to the gut and associated glands and organs Cleavage rapid cell divisions by which the embryo becomes divided into a number of smaller cells 9 gastrulation a set of cell movements that generates that three distinct cell layers ectoderm mesoderm and endoderm 9 by end of gastrulation ectoderm covers the embryo and the mesoderm and endoderm have moved inside 9 endoderm gives rise to the gut and to its derivatives such as liver and lungs the mesoderm forms the skeleton muscles connective tissues kidneys heart and blood ectoderm gives rise to the epidermis and the nervous system At the phylotypic stage head is distinct and the neural tube runs along the dorsal midline of the anteroposterior axis Differences in development in the model organisms particularly relate to how and when the axes are set up and how the germ layers are established and are mainly due to the different modes of reproduction and the consequent form of the earliest embryo Birds and mammals both of which form an extraembryonic membrane called an amnion are known as amniotes whereas amphibians and fish which do not form extra embryonic membranes are known as anamniotes The frog Xenopuslaevis is the model amphibian for developmental studies Blastomeres Cells deriving from cleavage divisions in animal embryos Cleavage occurs and inside this spherical mass of cells a uidfilled cavity the blastocoel develops in the animal region and the embryo is now called a blastula 15 19 Mesoderm and endoderm are located around the equator in the marginal zone and in the vegetal region respectively while the ectoderm which will eventually cover the whole of e embryo is still confined to the animal region 4 Manama eplboly 20 First external sign of gastrulation is asmall slitlike infoldingthe blastoporethat forms on the surface of the blastula on the future dorsal side This region is importantin development as it is the site of the embryonic organizer known as the Spemann organizer in amphibians without which dorsal and axial development will not occur 9 once gastrulation has started the embryo is known as a Estrula 21 Involution inward movement of future endoderm and mesoderm in the marginal zone through the blastopore by rolling under the lip as coherent sheets of cells 22 Epiboly ectoderm spreads downward to cover the whole embryo by a process 23 Archenteron precursor of the gut cavity the involuting layer of dorsal endoderm is closely applied to the mesoderm and the space between it and the yolkyvegetal cells 24 During gastrulationthe mesoderm in the dorsal region starts to develop into the notochord and the somites while the more lateral mesodermthe lateral plate mesoderm will later form mesodermderived internal organs such as the kidneys with anterior lateral plate mesoderm giving rise to the heart 25 Gastrulation is succeeded by neurulation the formation of the neural tube which is the early embryonic precursor of the central nervous system 9 the embryo is then called a neuru a Earliestvisible sign of neurulation is the formation of the neural folds which form on the edges of the neural plate an area of columnar ectoderm cells overlying the notochord Experimental approaches to studyingvertebrate development 26 Techniques for interfering with development can be very broadly divided into two types N 00 W W W and many experiments in developmental biology will use a combination of these two approaches a Classical experimental embryological techniques manipulate the embryo by physical interventionby removing or adding cells to cleavagestage embryos or transplanting blocks of cells from one embryo to another for example Genetics and genomics to disturb the expression of developmentally important genes by mutation gene silencing over expression or misexpressionexpressing the gene at a time or place where it is not normally expresse MRI and OPT can now be used to take images of live avian embryos inside the egg Not all techniques are equally applicable to all vertebrates Experiments involving the microsurgical manipulation of vertebrate embryos largely feature Xenopus and the chick X laevis is unsuitable for conventional genetic analysis because of its long generation time and its tetraploid genome However amphibian and avian embryos are robust to surgical manipulation and easily accessible to the experimenter at all stages in their development unlike those of mammals Blastomere removal identi es regions of the embryo that are essential for further development while transplantation experiments are used to test the developmental potential of a particular region of the embryo or to determine the time at which the fate of cells in particular location becomes irreversibly determined Fate mapping and lineage tracing reveal which cells in the early embryo give rise to which adult structures Fate maps show what a particular region of an embryo will develop into during normal development In Xenopus at the blastula stage cells that will eventually form the three germ layers are arranged in distinct regions and are accessible from the surface of the embryo Single blastomeres can be easily labeled with a nontoxic marker such as DiI which uoresces red or uoresceinlinked dextran or b ex ression of a uorescent protein such as GFP by injecting GFP RNA Electroporation injecting DNA into the embryo at the desired site with a fine pipette and pulses of electric current applied using very ne electrodes The current makes the membranes of nearby cells permeable to the injected DNA Celllineage tracing and fate mapping by dye injection or electroporation of nucleic acids is technically much more difficult in mammalian embryos than in Xenopus or the chick because the embryos are less accessible inside the mother Lineage tracing in the mouse is now done much more conveniently using transgenic embryos expressing a reporter gene in a particular set of cells under the control of the Cre loxP system or a reporter gene linked to a suitable promotor 0 Also useful for tracing later events in embryogenesis such as organ development the development of the nervous system and cell behavior in epithelia in which cells are continually being replaced such as skin and gut The animalvegetal axis is maternally determined in Xenopus and zebra sh Vertebrate development proceeds with respect to well defined anteroposterior head to tail and dorsoventral back to belly axes Mesoderm is produced after development has begun by signals from the vegetalregion cells acting on adjacent animalregion cells to specify a band of mesoderm around the equator of the blastula As the blastula develops the mesoderm becomes patterned along the dorso ventral axis so that it becomes subdivided into regions that give rise to different structures 34 First cleavage is parallel with the axis and often de nes a plane corresponding to the W 00 1 o 1 1 Equot 1 4 1 midline dividing the embryo into left and right sides 9second cleavage is the same plane at right angles to the rst and divides the egg into four cells 9 third cleavage is at right angles to the axis and divides the embryo into animal and vegetal halves each composed of four blastomeres Vgl mRNA is synthesized during early oogenesis and becomes localized in the vegetal cortex of mature oocytes moving into the vegetal cytoplasm before fertilization It is translated after fertilization and functions as an early signal for some aspects of mesoderm induction Xwntll provides one of the early signals required for dorsoventral axis speci cation a member of the Wnt family of signaling proteins related to the Wingless protein in Drosophila VegT has a key role in specifying both endoderm and mesoderm and its localization in the vegetal region Maternal mRNA encoding the Tbox transcription factor VegT is localized to the vegetal hemisphere and is translatedafter fertilization Localized stabilization of the transcriptional regulator Betacatenin specifies the future dorsal side and the location of the main embryonic organizer in Xenopus and zebra sh The spherical unfertilized egg of Xenopus is radially symmetric about the animal vegetal axis and this symmetry is broken only when the egg is fertilized Sperm entry sets in motion a series of events that de nes the dorsoventral axis of the gastrula with dorsla side forming opposite the sperm39s entry point See page 131 for common intercellular signaling proteins in vertebrate embryonic development Wnt roles at all stages in development Dorsoventral axis speci cation in Xenopus Limb development Receptors sevenspan transmembrane proteins During first cellcycle cortex rotates about 30 degrees against the underlying cytoplasm in a direction away from the site of sperm ent Cortical rotation an array of subcortical microtubules becomes oriented with their plus ends pointing away from the site of sperm entry and they act as tracks for the directed movement of proteins and mRNAs 9 leading to the relocation of maternal factors originally located at the vegetal pole such as XWnt11 mRNA and Dishevelled protein to sites on the equator opposite the sperm entry point creating asymmetry in the fertilized egg such that when the second cleavage division occurs only two of the four blastomeres inherit these maternal factors Cortical rotation can be prevented by irradiating the ventral side of the egg with UV which disrupts the microtubules responsible for transporting the dorsalizing factors Treated eggs are ventralized they are de cient in structures normally formed on the dorsal side and develop excessive amounts of bloodforming mesoderm However effects of UV irradiation are rescued39 by tipping the egg Because of gravity the dense yolk slides against the cortex thus effectively restoring rotation and the localization of maternal factors Canonical WntlBetacatenin pathway leads to the local stabilization of the protein Beta0catenin in the cells of the future dorsal region by preventing its degradation there 0 Maternal dorsalizing factors act by stimulating a signaling pathway Canonical Wnt pathway one of several signaling pathways that can be stimulated by Wnt proteins quot plasmamembvan w 4A degradation m r myzLyltlthH 45 Betaratenin L A adhesion molecules to the cytoskeleton 0 Ma ernalD tquot 39 39 39 39 39 39 butwhen bound to a 39destruction complex of proteins that includes the protein kinase 31m BM proteasomal degradation 46 A 39 L 39 39 39 Mn 1 the J L A I L LL prospective dorsal side ofthe embryo 7 By L n etam snin L 39 39 L ofthese cells andby L A c L u A u u 48 39 Wntproteini ieduiieuiui oligonucleotides causes loss of dorsal structures I 41 m quotrand to the dorsal region by maternal 39antagonists or inhibitors oant signaling present in the ventral region Inhibition L 39 39 y 39 39 strategy for restricting signaling to specific regions 39 39 A uiicLuy in pamway 1 c In 0 2 Dishevelled L A 39 39 nr uy inuiuituiy 39 ting on role playe by inhibition of GSKSBeta activity in establishing the future dorsal region 20 39 39 A r L 4 39 4 39 L blastulas 52 A A m A A e 39 lead to the format39 I as morphogens to pattern the embryo and set cell fates o Blastula organizer or Nieuwkoop center first signaling center that develops in the dorsalvegetal region in the Xenopus blastula sets the initial dorsoventral polarity in the blastula 53 Spemann organizer arises just above the Nieuwkoop center at the late blastulaearly gastrula stage and is crucial for further development of both the anteroposterior and dorsoventral axes ofthe embryo and the induction of the nervous system from me ectoderm 54 Dorsal and ventral regions are established by the fourcell stage 55 When cells fromthe dorsalvegetal region of a 32cell Xenopus embryo are grafted into the ventral side of another embryo this gives rise to a twinned embryo with two dorsal sides Cells from the graft itself contribute to endodermal tissues but not to the mesodermal and neural tissues ofthe new axis Donn 3203 nmhryo Raclplanl Mull embryo Anlmil Anlmal Dolsal Nieuwkoap v 39 host Vlgeml center ngnul Nleuwkmp center In contrast grafting ventral cells to the dorsal side has no effect 56 Graft ofthe Spemann organizer also produce twinned embryos but in this case the grafted tissue forms the notochord ofthe secondary axis 57 By the 16 to 32cell stage Betacatenin protein can be detected in nuclei on the dorsal side where invegetal cells expressing VegT it activates zygotic genes such as siamois which is involved in the induction of Spemann organizer function VegT is also required to induce expression ofthe genes encoding Nodalrelated proteins signaling proteins that induce mesoderm Nodal members ofthis protein family are key factors in mesoderm induction in all vertebrates and in the frog they are known as the Xenopus Nodalrelated factors ans Dharma essential for inducing the organizing function ofthe shield and the development of head and trunk regions 21 22 The origin and specification of the germ layers esoderm give rise to notochord muscle heart and kidney and bloodforming tissues Ectoderm give rise to epidermis ofthe skin and cells thatdevelop into the nervous system Endoderm give rise to the gut and its associated organs such as the lungs liver and pancreas 58 Fate maps tell us which tissues are generated from particular regions ofthe embryo A fate map of the amphibian blastula is constructed by following the fate of labeled cells 59 Individual cells can be identifies with respect to the animalvegetal axis defined by pigmentation and dorsoventral axes defined by the sperm entry point ne way of making a fate map is to stain various parts of the surface of the early embryo with a lipophilic dye such as Dil and observe where thelabeled region ends up 0 u quot 39 l b quotdextran 1quot h l l 39 molecules Future mesoderm forms from a beltlike region the marginal zone around the equator of the blastula 60 During gastrulation the marginal zone moves into the interior through the dorsal lip of the blastopore which lies above the Nieuwkoop center 61 Fate map of germ layem 1 Mesoderm dorsal mesoderm gives rise to the notochord followed going ventrally by somites which give rise to muscle tissue lateral plate which contains heart and kidney mesoderm and blood islands tissue where hematopoiesis first occum in the embryo 62 Differences between the future dorsal and ventral sides ofthe animal hemisphere the epidermis comes mainly from the ventral side of the animal hemisphere whereas the nervous system comes from the dorsal side After neural tube formation the epidermis spreads to cover the whole of the embryo 63 Fate map does not correspond exactly to a neat set of axes at right angles to each other 64 As a result of cell movements during gastrulation cells from the dorsal side of the blastula give rise to some ventral parts of the anterior end of the embryo such as head as well as to dorsal structures and will also form some other ventral structures such as the heart 65 The ventral region gives rise to ventral structures in the anterior part of the embryo but will also form some dorsal structures posteriorly Fate map laleml View Fate map dorsal View Animal Animal epidermis Ventral 1 Dorsal marginal nolochord zone Vegelal ngetal 23 In Xenopus the endoderm and ectoderm are specified by maternal factors but the soderm is induced from ectoderm by signals from the vegetal region 66 Animal cap cells form mesoderm obmined by preilabeling the animal region ofthe blastula with a cellilineage marker and showing that the labeled cells form the mesoderm ecmderm Animal animal cap cells nolochord fequatorial cellsi Dorsal Venlral I quotnew we 3933999601 an muscle neural lube epidermis blood a assesses 9000 mm mmquot vegelal cells Vegelal early I g I I Animal ectoderm animal cap cells In nchyrne Vanna equaloria cells Dom J 5555000 a Menguch o va oc c epider 5 blood vegetal cells V8985 undiflerentiated vegetal tissue 67 Differentiation of a mesodermal tissue such as muscle inthe explant system appears to d p nd on a community e fect


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