Genetic engineering has enabled new applications in fashion, materials, and agriculture. Researchers have created fluorescent dresses by genetically engineering silkworms to produce fluorescent silk fibers. They have also engineered silkworms to produce artificial spider silk with improved elasticity and strength. Other examples include developing a fluorescent fish that detects estrogen, stronger dogs by deleting a muscle gene, and the first blue rose through genetic modifications. While this technology holds promise, it also raises ethical issues that require guidelines and oversight.
Transgenic manipulation of animal embryos and its applicationDeveshMachhi
INTRODUCTION
Genetic manipulation in animal for higher productivity is also called genetic engineering, refer to the alteration of the gene of an organism.
Organisms containing integrated sequences of cloned dna (transgenes), transferred using techniques of genetic engineering (to include those of gene transfer and gene substitution) are called transgenic animals.
Transgenic technology has led to the development of fishes, live stock and other animals with altered genetic profiles which are useful to mankind.Genetically modified animals are proving ever more vital in the development of new treatments and cures for many serious diseases.
Transgenesis is a radically new technology for altering the characteristics of animals by introducing the foreign genetic material.
CONTACT: devmac1323@gmail.com
Transgenic manipulation of animal embryos and its applicationDeveshMachhi
INTRODUCTION
Genetic manipulation in animal for higher productivity is also called genetic engineering, refer to the alteration of the gene of an organism.
Organisms containing integrated sequences of cloned dna (transgenes), transferred using techniques of genetic engineering (to include those of gene transfer and gene substitution) are called transgenic animals.
Transgenic technology has led to the development of fishes, live stock and other animals with altered genetic profiles which are useful to mankind.Genetically modified animals are proving ever more vital in the development of new treatments and cures for many serious diseases.
Transgenesis is a radically new technology for altering the characteristics of animals by introducing the foreign genetic material.
CONTACT: devmac1323@gmail.com
Introduction
History
Landmarks Events in Transgenic Livestock Research
Techniques/ Method for Gene Transfer
Examples of transgenesis
Importance
Application
Limitation
Issue related to Transgenic Technology
Ethical concerns and how to Overcome
Introduction
Definition
History
Why are the transgenic animals being produced
Transgenic mice
Mice: as model organism
Methods of creation of transgenic mice
knock-out mice
Application of transgenic mice
Conclusion
References
One mutational event is the integration of the viral genome into the host chromosome, The exogenous forces responsible for this event range from UV and ionizing radiation exposure to a defect in the virus itself.[a.3]
An additional event important in MCPyV-induced carcinogenesis is the mutation of the viral genome in a manner that renders the virus unable to replicate. The most common mutations occur in the carboxy terminus of LT, which generate a truncated LT that lacks the helicase domain required for replication yet preserve its oncogenic functions.[a.3]
Persistent expression of truncated LT and sT from the integrated MCPyV genome can inactivate pRb tumor suppressor function and promote and/or deregulate cap-dependent translation initiation, respectively. [a.3]
Ultimately, the cells in which integration of a replication-defective MCPyV is successful become addicted to viral oncogene expression and undergo clonal expansion and neoplastic progression to cause the development of MCC.[a.3]
Introduction
History
Landmarks Events in Transgenic Livestock Research
Techniques/ Method for Gene Transfer
Examples of transgenesis
Importance
Application
Limitation
Issue related to Transgenic Technology
Ethical concerns and how to Overcome
Introduction
Definition
History
Why are the transgenic animals being produced
Transgenic mice
Mice: as model organism
Methods of creation of transgenic mice
knock-out mice
Application of transgenic mice
Conclusion
References
One mutational event is the integration of the viral genome into the host chromosome, The exogenous forces responsible for this event range from UV and ionizing radiation exposure to a defect in the virus itself.[a.3]
An additional event important in MCPyV-induced carcinogenesis is the mutation of the viral genome in a manner that renders the virus unable to replicate. The most common mutations occur in the carboxy terminus of LT, which generate a truncated LT that lacks the helicase domain required for replication yet preserve its oncogenic functions.[a.3]
Persistent expression of truncated LT and sT from the integrated MCPyV genome can inactivate pRb tumor suppressor function and promote and/or deregulate cap-dependent translation initiation, respectively. [a.3]
Ultimately, the cells in which integration of a replication-defective MCPyV is successful become addicted to viral oncogene expression and undergo clonal expansion and neoplastic progression to cause the development of MCC.[a.3]
Definition of adaptation
The importance of adapting
Division of adaptation …
Biomes of our Earth
What it the adapted of ocean biomes
What it the adapted of Desert biomes
Adaptations – an inherited characteristic that helps an organism to survive long enough to reproduce more successfully in its changing environment.
the process of change by which an organism or species becomes better suited to its environment.
1- Maintain the balance of ecosystems and biodiversity.
2- Organisms that have not been able to adapt to changing environmental conditions that have become extinct.
3- When determined to change something in the behavior of living organisms we follow the theory of adaptation.
4- Simulation.
Recent Breakthroughs in Genetic EngineeringSamar Biswas
Genetically engineered immune cells are saving the lives of cancer patients.
Precise Gene Editing in Plants.
DNA-editing breakthrough could fix 'broken genes' in the brain, delay ageing and cure incurable diseases
The Genetic engineering could slow aging, reverse blindness.
The genetic engineering that could change humanity.
Chinese researchers have genetically modified a human embryo.
CONCEPT
HISTORY OF XENOTRANSPLANTATION
IMPORTANCE OF XENOTRANSPLANTATION
CHOOSING OF DONOR SPECIES
XENOTRANSPLANTATION REJECTION
GUIDELINES ON XENO-TRANSPLANTATION BY ICMR
RECENT RESEARCH ON XENOTRANSPLANTATION
It's include all the details about the transgenic technology.all the techniques like micro injection,SCNT,pro nuclear injection method.It include all the Transgenic mice bird and fish.
Similar to What is the latest fashion-Genetic Engineering (20)
Community ecology, study of the organization and functioning of communities, which are assemblages of interacting populations of the species living within a particular area or habitat.
In terms of biomass, the greatest migration in the world is the migration of Zooplankton .
Zooplankton migration is different because it moves up and down through the ocean's depths rather than traversing a landscape.
The evolutionary development or history of a species or of a taxonomic group of organisms (The phylogeny of a group of taxa (singular: taxon) (species, etc.) is its evolutionary history)
Detailed consideration of the mechanisms of
reproduction and look instead at human fertility patterns,
and at the factors, both natural and artificial, that may
influence them.
The tiny fertilized egg sitting in the oviduct now has to
perform a heroic task. It must somehow communicate its
presence to the mother and convert the whole of her physiology
and anatomy from a cyclic reproductive state to a
pregnant one.
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
This pdf is about the Schizophrenia.
For more details visit on YouTube; @SELF-EXPLANATORY;
https://www.youtube.com/channel/UCAiarMZDNhe1A3Rnpr_WkzA/videos
Thanks...!
Cancer cell metabolism: special Reference to Lactate PathwayAADYARAJPANDEY1
Normal Cell Metabolism:
Cellular respiration describes the series of steps that cells use to break down sugar and other chemicals to get the energy we need to function.
Energy is stored in the bonds of glucose and when glucose is broken down, much of that energy is released.
Cell utilize energy in the form of ATP.
The first step of respiration is called glycolysis. In a series of steps, glycolysis breaks glucose into two smaller molecules - a chemical called pyruvate. A small amount of ATP is formed during this process.
Most healthy cells continue the breakdown in a second process, called the Kreb's cycle. The Kreb's cycle allows cells to “burn” the pyruvates made in glycolysis to get more ATP.
The last step in the breakdown of glucose is called oxidative phosphorylation (Ox-Phos).
It takes place in specialized cell structures called mitochondria. This process produces a large amount of ATP. Importantly, cells need oxygen to complete oxidative phosphorylation.
If a cell completes only glycolysis, only 2 molecules of ATP are made per glucose. However, if the cell completes the entire respiration process (glycolysis - Kreb's - oxidative phosphorylation), about 36 molecules of ATP are created, giving it much more energy to use.
IN CANCER CELL:
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
introduction to WARBERG PHENOMENA:
WARBURG EFFECT Usually, cancer cells are highly glycolytic (glucose addiction) and take up more glucose than do normal cells from outside.
Otto Heinrich Warburg (; 8 October 1883 – 1 August 1970) In 1931 was awarded the Nobel Prize in Physiology for his "discovery of the nature and mode of action of the respiratory enzyme.
WARNBURG EFFECT : cancer cells under aerobic (well-oxygenated) conditions to metabolize glucose to lactate (aerobic glycolysis) is known as the Warburg effect. Warburg made the observation that tumor slices consume glucose and secrete lactate at a higher rate than normal tissues.
A brief information about the SCOP protein database used in bioinformatics.
The Structural Classification of Proteins (SCOP) database is a comprehensive and authoritative resource for the structural and evolutionary relationships of proteins. It provides a detailed and curated classification of protein structures, grouping them into families, superfamilies, and folds based on their structural and sequence similarities.
This presentation explores a brief idea about the structural and functional attributes of nucleotides, the structure and function of genetic materials along with the impact of UV rays and pH upon them.
Nucleic Acid-its structural and functional complexity.
What is the latest fashion-Genetic Engineering
1.
2. Dream comes true
With
Genetic Engineering
Prepare by :
Sumaiah Alghamdi- Norah Alhoshani
Nora alkahtani -Hind alsubaie
Submitted to :
Dr. Zinab qurni
3. Content
• Introdiction
• Example of genetic engineering application
• Reengineering a transmembrane protein
• Gentically modified insect
• Egg engineering
• References
6. 1-Fluorescent dresses ..cont
• The researchers inserted glowing
proteins, borrowed from corals and
jellyfish, into the silkworm genome near
the gene for the silk protein fibroin.
They then raised more than 20,000
transgenic silkworms, which expressed
fibroin proteins with the fluorescent
molecules attached, and collected their
colorful cocoons.
8. 2-Silkworms produce artificial spider silk
• A research has succeeded in producing transgenic silkworms using
piggyBac capable of spinning artificial spider silks.
• PiggyBac is a piece of DNA known as a transposon that can insert
itself into the genetic machinery of a cell.
• The genetically engineered silk protein produced by the transgenic silkworms
has markedly improved elasticity and strength approaching that of native
spider silk.
10. 3- Fluorescent fish
• Researchers in Hong Kong have developed a fish that glows in the
presence of estrogen-like chemicals called estrogenic endocrine disruptors
• Scientists inserted a green fluorescent protein gene into the genome of
the medaka fish and positioned it next to a gene that senses estrogen
11. 4-Stronger dogs
• Scientists in China say they are the first to use
gene editing to produce customized dogs.
They created a beagle with double the amount
of muscle mass by deleting a gene called
myostatin.
• The dogs have “more muscles and are
expected to have stronger running ability,
which is good for hunting, police (military)
applications,”
12. 5- Blue rose
• researchers in Suntory’s Institute for Plant Science using advanced
technology to reduce the levels of red/purple color and isolating the blue
pigment gene from pansy and hybridizing to that of a rose, could this
tinge of blue be created.
• The transgenic carnation and rose also contain selectable marker genes for
herbicide resistance in carnation and antibiotic resistanc in rose.
13. 6- Invisibility cloaks
• Researchers using arrays of minuscule 'elements' that bend, scatter,
transmit or otherwise shape electromagnetic radiation in ways that no
natural material can. And many metamaterials researchers are trying to
make cloaking a reality, can used for military
19. Main areas of muscle weakness in different types of
dystrophy
20. Dystrophin Glycoprotein Complex (DGC)
• Dystrophin and its associated proteins
localize to the muscle plasma membrane,
acting as a linker between cell “skeleton” to
connective tissue in muscle fibers.
• Mutations that disrupt the dystrophin
glycoprotein complex (DGC) cause muscular
dystrophy.
21. Sarcoglycan sub complex
• The sarcoglycan sub complex within the DGC is
composed of 4 single-pass transmembrane
subunits: α-, β-, γ-, and δ-sarcoglycan.
• Recessive loss-of-function mutations in genes
encoding α-, β-, γ-, and δ- sarcoglycan cause the
limb girdle muscular dystrophies (LGMD) type
2D, 2E, 2C, and 2F, respectively.
22. limb girdle muscular dystrophies (LGMD)
• The sarcoglycan complex is localized at the muscle
membrane, and loss-of-function mutations in mice
and humans result in the absence of plasma
membrane–associated staining.
• LGMD 2C patients have mutations in SGCG, the
gene encoding γ-sarcoglycan.
23. Exon skipping
• Is a type of gene therapy by using
which blocks translation using
antisense oligonucleotide.
• is a strategy in which an antisense
oligo-nucleotide is used to coax cells
into skipping an exon (region of
genetic instructions), splice together
remaining exons and produce a
functional protein.
25. Mini_ Gamma rescues Drosophila muscular
dystrophy
• Full-length murine γ-sarcoglycan
(mGSG) localized to the sarcolemma
when expressed in Sgcd840 muscle
,indicating that the mGSG normally
translocates in Drosophila muscle.
26. Mini_ Gamma rescues Drosophila muscular
dystrophy
• Expression of murine MiniGamma
showed the same distinct plasma
membrane localization when expressed
in Sgcd840 flies.
• Expression of MiniGamma in Sgcd840
hearts also showed plasma membrane–
associated staining in the thin-walled
heart tube structure.
27. Measure Drosophila heart function
• Optical Coherence Tomography (OCT) was
used to measure heart tube dimension during
both contraction and relaxation.
• Sgcd840 flies had dilated heart tubes with
significantly increased end systolic dimension
(ESD) compared with WT
• Expression of Mini-Gamma in the heart tube
was sufficient to restore ESD to WT
dimensions.
30. Introduction
Insect responsible for economic and
social harm worldwide through the
transmission of disease to humans and
animals, and damage to crops.
Their genetic modification has been
proposed as a new way of controlling
insect pests.
However, regulatory guidelines
governing the use of such technology
have not yet been fully developed.
31. Current Insect Control Strategies
• Indoor spraying.
• Use of insecticide-treated bed nets
Insecticides
• Is the sterile insect technique in which laboratory-reared male insects
• Removal of breeding sites around human habitations.
Alternative Control Strategies
32. Genetic Modification of Insects
• Genetically modified (GM) insects are
produced by inserting new genes into their
DNA.
• Many genes have been identified that can alter
the behaviour and biology of insects.
• When these genes are inserted into an insects
genome they are called transgenes, by
injecting DNA containing the desired genes
into the eggs of insects.
33. Researchers use a wide variety of transgenes, derived
from a variety of organisms, to modify insects:
Marker genes are used to make the insects fluoresce, these allow
researchers to distinguish them from the unmodified variety, which
is important for monitoring them in the environment.
Lethal genes cause the insect to die, or make it unable to
reproduce.
Refractory genes confer resistance to a particular pathogen
rendering the insect unable to transmit the disease any longer.
34. Potential Control Strategies:
Scientists have proposed two distinct strategies involving
the release of GM insects.
1. Population suppression: is a method in
which insects are engineered to ensure that
when they mate with wild individuals no
viable offspring are produced or producing
progeny that died before they can transmit
disease.
2. Population replacement: strategies involve
permanently replacing wild populations of
insects with GM varieties( anti-pathogen gene)
that have been altered to render them less able
to transmit disease..
35.
36.
37. Paratransgenesis insect
Paratransgenesis was first conceived by Frank
Richards (1996)
Paratransgenesis is a technique that attempts to
eliminate a pathogen from vector populations
through transgenesis of a symbiont of the
vector. The goal of this technique is to control
vector-borne diseases.
Engineer Triatominae express proteins such as
Cecropin A that are toxic to T. cruzi or that block
the transmission of T. cruzi.
38. INSECTS GENES CHARACTER MODIFIED
1. Anopheles SM 1 Disease causing ability
destroyed
2. Culex Defensin Disease spreading ability is
lost
3. Silkworm Spider flagelliform
silk
Enhances quality of silk
protein
4. Wolbachia Attacin and
Cecopin
Infective capacity is lost
5. Xylella S 1 Disease causing capacity is
absent
Introduced transgenes in insect
42. Conclusion
The Potential Benefits of GM Insect Strategies
They would target only a single insect pest species,
leaving beneficial insects unharmed.
GM insects could reduce the need for insecticides
and any associated toxic residues in the
environment.
When used in disease control programmes GM
insects would protect everyone in the area.
44. EGG ENGINEERS
In a technical tour de force, Japanese researchers created eggs and
sperm in the laboratory. Now, scientists have to determine how to
use those cells safely and ethically
45. Introduction
• Ince last October, molecular biologist Katsuhiko Hayashi has received around a dozen e-mails
from couples, most of them middle-aged, who are desperate for one thing: a baby. One
menopausal woman from England offered to come to his laboratory at Kyoto University in Japan
in the hope that he could help her to conceive a child.
• The requests started trickling in after Hayashi published the results of an experiment that he had
assumed would be of interest mostly to developmental biologists. Starting with the skin cells of
mice in vitro, he created primordial germ cells (PGCs), which can develop into both sperm and
eggs. To prove that these laboratory-grown versions were truly similar to naturally occurring
PGCs, he used them to create eggs, then used those eggs to create live mice. He calls the live
births a mere ‘side effect’ of the research, but that bench experiment became much more, because
it raised the prospect of creating fertilizable eggs from the skin cells of infertile women. And it
also suggested that men’s skin cells could be used to create eggs, and that sperm could be
generated from women’s cells.
46. BACK TO THE BEGINNING
• In the mouse, germ cells emerge just after the first week of embryonic
development, as a group of around 40 PGCs2. This little cluster goes on to
form the tens of thousands of eggs that female mice have at birth, and the
millions of sperm cells that males produce every day, and it will pass on the
mouse’s entire genetic heritage. Saitou wanted to understand what signals direct
these cells throughout their development.
• Over the past decade, he has laboriously identified several genes including
Stella, Blimp1 and Prdm14 that, when expressed in certain combinations and
at certain times, play a crucial part in PGC development 3–5. Using these genes
as markers, he was able to
47. BACK TO THE BEGINNING
select PGCs from among other cells and study what happens to them. In 2009,
from experiments at the RIKEN Center for Developmental Biology in Kobe,
Japan, he found that when culture conditions are right, adding a single ingredient
bone morphogenetic protein 4 (Bmp4) with precise timing is enough to convert
embryonic cells to PGCs2. To test this principle, he added high concentrations of
Bmp4 to embryonic cells. Almost all of them turned into PGCs2. He and other
scientists had expected the process to be more complicated.
48. Hayashi way
• Hayashi tried to use epiblast cells Saitou’s starting point but instead of using
extracted cells as Saitou did, he tried to culture them as a stable cell line that
could produce PGCs. That did not work. Hayashi then drew on other research
showing that one key regulatory molecule (activin A) and a growth factor (basic
fibroblast growth factor) could convert cultured early embryonic stem cells into
cells akin to epiblasts. That sparked the idea of using these two factors to induce
embryonic stem cells to differentiate into epiblasts , and then to apply Saitou’s
previous formula to push these cells to become PGCs. The approach was
successful.
• To prove that these artificial PGCs were faithful copies, however, they had to be
shown to develop into viable sperm and eggs.
49. Cont..
The process by which this happens is complicated and ill understood, so the
team left the job to nature Hayashi inserted the PGCs into the testes of mice
that were incapable of producing their own sperm, and waited to see whether
the cells would develop6. Saitou thought that it would work, but fretted. “It
seemed like a 50/50 chance, But, on the third or fourth mouse, they found
testes with thick, dark seminiferous tubules, stuffed with sperm. The team
injected these sperm into eggs and inserted the embryos into female mice.
The result was fertile males and females
50. Cont..
• They repeated the experiment with induced pluripotent stem (iPS) cells
mature cells that have been reprogrammed to an embryo-like state. Again, the
sperm were used to produce pups, proving that they were functional — a rare
accomplishment in the field of stem-cell differentiation, where scientists often
argue over whether the cells that they create are truly what they seem to be.
“This is one of the few examples in the entire field of pluripotent-stem-cell
research where a fully functional cell type has been unequivocally generated
starting from a pluripotent stem cell in a dish,” says Clark.
51.
52. Cont..
They expected eggs to be more complex, but last year, Hayashi made PGCs in
vitro with cells from a mouse with normal colouring and then transferred them
into the ovaries of an albino mouse. The resulting eggs were fertilized in vitro
and implanted into a surrogate.
53. CLINICAL RELEVANCE
Saitou and Hayashi have found that the offspring generated by their technique
usually seem to be healthy and fertile, but the PGCs themselves are often not
completely ‘normal’. For example, the PGCs can produce eggs that are fragile,
misshapen and sometimes dislodged from the complex of cells that supports them1.
When fertilized, the eggs often divide into cells with three sets of chromosomes
rather than the normal two, and the rate at which the artificial PGCs successfully
produce offspring is only one-third of the rate for normal in vitro fertilization (IVF).
54. CLINICAL RELEVANCE
But the most formidable challenge will be repeating the mouse PGC work
in humans. The group
has already started tweaking human iPS cells using the same genes that
Saitou pinpointed as being important in mouse germ cell development, but
both Saitou and Hayashi know that human signalling networks are different
from those in mice. Moreover, whereas Saitou had ‘countless’ numbers of
live mouse embryos to dissect, the team has no access to human embryos.
Instead, the researchers receive 20 monkey embryos per week from a nearby
primate facility .
Yi Zhang, who studies epigenetics at Harvard Medical School in Boston,
Massachusetts, and who has been using Saitou’s method, has also found
that in vitro PGCs do not erase their previous epigenetic programming as
well as naturally occurring PGCs. “We have to be aware that these are PGC-
like cells and not PGCsPGCs,”
