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OCR for page 304
1~ ~rIAL OF MI~IAI~ E~06
. .
V.E. Pa~oar~u
detraction
Uses of Mi~nipulation
Warred con }fly the promise of biology for i - ~renents in health
arm z~pr~ctive performarx~e in humans arm animals, scientists Con
diverse fields have recently been aE~1yirg manipulative e~ri~tal
Unique to the embryos of a wide range of Species. At both Alar
arm cellular levels, material Is being awed, subrace, or all for
the a~li~nt of ~ as diverse as stying embryonic inaction
and prying genetically superior agricultural animals. He growth of
Ear biology has awed a new Tension to the venerable practice of
, e _ . a ha e e ha _ a pa ca a ~ a e _ as ~ ~ , ~
embryo manipulation, pairing ~=aalble the induction of Pacific genetic
martial or the ~rh~tion of Diogenes gene avidity in Be developing
embryo. He pacer of this a~rnadh will be realize anly In `~inatic~n
with a consideration of develops—1 pro cn He level of
organism as a whole.
~ manipulations to be described in this paper are of a cellular
rather Han a rnucl~a' or genetic variety. Although He abject of the
experiments was not always primarily embryonic ration, together the
st ~ ies provide a ~ ium of information on the capacitor of the
organism to compensate for cellular perturtations during preimplantation
stages of development. m e emphasis will be on the upward regulation of
~~l number, ~ other wards, the ability of an embryo to ccrqxYnsate for a
Decrease in cell number at different embryonic stages.
Types of Manipulation
The indeterminate cleavage of mammals means that A] fates are not
precisely foxy face the outset but Ether that calls retain a high degree
of devel~tal plasticity or regulative capacity thrift the Fly
stages of erdbryogenesis. Leper. evidence sorts the contention
that developmental potential of cog Is is gradually nal~ as de~relopnent
progresses and oelis beeline established in particular pathways. Den the
dentin of differentiation of a ~1 ~ or region of the embryo has }wry
i~ev~bly established, its fate is the saIre as its potential arm it can
be Ed to be committed or detail. me Canine of this Modular
determination remains elusive.
~ 3C]
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Anion mania n ~ a c~n~taw of Varietal embryology.
~ a~itic~n ~ ~ investigatic~n of Of fate and Via of irxlivi~1
As, He organization of He Kayo as a whole can also be I
using m~cnmanipulatic~n Tunis;. He i~actia~s sixteen ~1 1= or
grumps of Airs, the influence of parts on He Ale, arm ~ Ale of
Optic Bets ~ Ryes can all ~ ~~ Dig
cellular ~cmnanipulation. Isolation of parts of an rye to Done
there [~ - C: separate f`=u He rest of the Are either ~ ~~,
in Chic sit; or in He uterus ~ off -bible procedure. As met.
tests the ~nt;~1 of a ~ll or tissue for Irene: develc~t by
altering cell arm tissue interactions and, ~ explants, by r~rir~ the
Stir influence of the maternal Limit.
Alternatively, part of an eribryo can be destroyed or red arm the
embryo gram in vitro or ir1 the uterus. He f~ develc~rent of the
embryo will provide evidence as to the illportar~ of the misfire part to
the develc~nt of He whole arm the capacity of the embryo to USA
for Age. cel Is or tissues may also be Bird by transpla~aticxn or
Bard between different embryos. In this type of e~peri~nt, genetic
Nan; aims for He identification of ache contribution of each Sapient
in the Opposite, chivalric embryo. Finally, cells or parts may be added
to an ~erw~ complete embryo, arm ~ an extend form of this pmc~~re,
whole erbryos can be aggregated together. He sucxxssful covenant of
Nitric animus foliate ache aggr~ati~ of two or Ore cx - lete embryos
is a tint to the relative capacitor of ~ Orgy mammalian The.
Ration in Arabian embryos
E - rinds embryologists have made good use of the! irmate Opacity
of the n~nalian embryo to adjust its devel~ntal p~rmn to Ate
for Actions. Fin the embryo's point of view, this feature ~
pr~nnably advantageous, pr~nricling a measure of flexibility to Add
are Sensate for a Terse coalitions that might nicer during gestation.
In an animal as complex as the mammal, with a dynamic maternal-embryonic
and mat ~ -fetal interaction during gestation, this degree of
flexibility provides some insurance for the considerable rep ~ tive
investment of each pregnancy.
As a practical consideration, parti~,larly ~ the manipulation of
human embryos, this regulative able ity allows come leeway in the varicose
techniques associated with artificially desisted ccnosption. The fact
that the embryo will be able to tolerate I-== than ideal conditions and
still develop into a normal individual broadens the range of manipulations
that can ethically be applied In mrerc~ainq infertility In humans. In
agri~1tura1 animals it will define the limits of ecx~im1ly vi~hie
pro. Incus, it is all the refire important to determine the limits of
the r ~ ative capacity at all stages of early ~ibr~rogenes~s and to
determine differences between different species. In doing so we will be
learning about the basic processes of development as well as establishing
a firm and reasonable basis for intervention in the reproductive process.
305 -
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Use
Shxtvina Radiation
I;3b oratory arx] caustic
ties
Prein~lantati~ Devel~t
The Ian embryo Avers ~ ~ alit as it cot ~
ally enters the uterus to he erx] of this pro=, alto he
stage at which it d~ so varies and mods (-table 11. Iste ~
cleavage, aids of the embryo Thick up to this tone have been silnilar'
logy Cited i;, begin ~ Batten ~ one ark and Space
as a peels - e to formation of- the blas~st. With blast~e formation
cams the first avert sign of phrenological differentiation of twc ~11
go;, the inner cell man= (ICE) and the alter layer of t_ form
as the result of a divergence In gene expression In Me ~ ~l 1
p~latic~ns. Ihis fort differentiation into disti~b ~11 types also
heralds the earliest c~nitnent of Ells ~ Pacific cell lies an]
results fmn the restriction In potential of the previously tatipotent or
at least multipc~t blasts. Folly hatting Frau the zone
pellu:ida, We blasters In scan species, such as the horse, Prose arm
human, remain spherical, whereas ~ ethers, such as pig err] can, it
experts and elevate; considerably before implantation. We tin arm
stage at implantation varies ~ different species, as do maternal-fet~
interactions resulting in distinctively different placentstion types.
Obese early emerita of prei~r~?lantation ~velc~t have been well
studied In the manse from botch Tr~rphologi~a1 arx] ex~ri~n~ Dives
arx] a ably full picture has been drawn.
Is such information is still Ditty.
- ~ ~ ~ - -
But for over species of
~r~ologi~]ly, the ~ryc6
of ok Brian Is rile the ~se, ash the tip of
events varies (liable 1~. It is 1~oi~ evident foxy ex`~ri~ntal work
that ctiff~rxxs in tinier are not ache anly distinctions arm that Eerbr~6
of different species with He sag cell ~ or at the same
rrSholoai~1 stare mav be fi0ar~t~llv different in the Dee of
—^~ - ~—- _ ~ ~ _
determination that has taken place and ache relative potential of
blast~e
P - Gelatin are cell Potential During Cleavage arm Blas~lation
Be Trot Sargent test of ~11 F~rtia1 ~ whether an isolate
rbryonic ~11 is totip~ent, that is, why it is Feeble of r~ulatir~
its devel~nt such that it can Agate for an overa:~1 reduction in
Chronic ~~l ~ arm produce a viable off~prir~.
It Nat be
,, ~
determined if any or all of the calls of an early embryo have this
veracity in order to fully define regulation. For example, development of
one blasts mere from a 2-cel1 embryo is an indication of individual
blastorere totipatency, but both blastc meres must be shown to develop
normally before totipotency of 2-cel1 blastomeres in general can be
claimed. Likewise, the production of even a single pair of identical
twits Rae bisection of an embryo is proof Nat twc halves can be
- 3~)6
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tatipotent, but the plane of bisection with rent to any airy in
the embryo nest be insiders. For the polarized blast~yst, it Is
evident Mat ply bisection of the ICM, giving balance half~ryos, can
result in manful ~i~ir~ (Garner 1972; 1974) err] so totipot~y of
half - Blasts In gereral caveat be claim - .
1) I~o~tory Species: In the mouse, the ~tia1 of single
isolate blast to form embryos; apart; to be reprice relatively
early (gable 2~. Single blasts fmn the 2~11 stage, but ret later
stags, are table of developir~ into Replete, viable off~E?rir~ (lambda
& laymen 1983~. Although individual blasts fmn ~,ryo6 up to at
let the 8~el1 stage al - ar to be totip~t In terms of the tissues
they can produce in a *Libra (Kelly 1975), they are not Table of
on anizir~ into viable fetuses in isolation (Pan sent 1976~. In the rat, a
complete egg cylinder was reported to have developed from one blastccere
of the 2-cel1 stage, although development stopped shortly thereafter
ONicholas & Hall 1942~. In more recent experiments, identical twin
offspring have been proud frail 2-cel1 blasts meres of the rat Mat
et al, 1989~. Single blasts meres frill 4- and even 8-oel1 stages of the
rabbit have shown toti~tency (Seidel 1952, 1956; Mbore, Adams & Rowson
1968) indicating a greater regulative capacity of cleaving blasts
this specie; than In the ~use.
me survival of half mouse embryos can be as high as 65 Extent for
the 2~l stage (~ ~ Mt:~ren 1983), arm aver 45 brunt for the
4 - Bell (Rossant 1976), marula (1~a & MbIar~ 1983; Nagashi~na et al.
1984), arm blast~rst (Gardr~ 1974~. Hanover, survival of bath halve of
the sex embryo has box d~nstra~ orgy for the 2 cell stage arm the 8-
to 16 - x11 stage (MOusatafa & Hahn 1978; Garter & 13raunadk 1981; ]~da
& Wren 1983; Naga~hi~a et al. 1984; Table 2~. A recent sty of late
rula~e~rly blandest stages of rabbit eF6bryc~s indicate that half
embryo survival arc] the survival of botch halves Is Educible in this
Species as well (Yang & Foote 1987~.
2) Drastic species: Work in dc~restic Lies has been 1~:
schematic but theta has been considerable sum: In the production of
i~ti~1 florins of several busies. Ibtip~ of isolated, indivi~
'amp blast ~ maintained up to the 8~11 stage (1~ & Lore
1974; Willadsen 1981), but no Are than three of We blasts from a
4 ~ 11 embryo and one of the blast ~ f m n an 8 ~ 11 embryo have yet
been proved totipo tent. This may be a technical failure but it could also
represent a biological restriction in the potential of some of the
blastcceres by these stages and indicate that the morphologically similar
blastcoeres have already undergone restriction in potential. In another
experiment, 4 identical quadruplets were born from a single sheep embryo
that had been quartered at the 8-cell stage QWilladsen 1981). If these
quarters ccnsisbed of daughter-oell pairs from the 4-oel1 stage, as seem
likely fr all the procedure used (Willadsen 1980), then this result ~ ght
argue that all 4 blasts meres at the 4-cel1 stage do indeed retain
totipotency. A high rate of survival of half embryos to term has been
demonstrated for the 2-cel1 stage through the blasts cyst stage in sheep,
and both haves of all of the stages have produced ic3~ti=1 twin
offspring (Willadsen 1979, 1980; Gatica et al., 1984~.
3D, -
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1` relative potential of single blasts of con euibry=; has
not Aim detrain, bet barter embryos fmn the Smell stage have
a set of triplets (Willadsen & Polge 1981) arm fmn Me
32 64 - Bell Facula stage, 4 sets of thins (Will~sen et al. 1981),
indicating bat at least scene stems of blasts at muse stab are
totipotent. Bisection of OC*J embryos has resulted in fur
~ctic~n of identical twins at the early ~ru:la stage to the
blasts stage (Oziletal1982; I~thet al. 1983; Oz;1 1983;
Willis et al. 1984) arm ~ high ram; of half embryo survival. P - orb
louses of ~ryo6 late ~ gestation, hover, clearly indicate that not
all embryos that implant am capable of complete develc~rent. A shady of
the cam- of fetal mortality in these ~ might well pr~ride insight
ins Fusible z~rictions of Gentian or regulative Acid.
Little work he been polished on manipulation of ather darestic
dies. In the horse, 3 offspring have been sport fmn bid
2-8 cell stages, altha ~ no twin pairs, and 4 offspring comprising 2 sets
of twins have been obtained from isolated 4-cel1 blasts meres (Allen 1982;
Allen & Pashen 1984). Thus, at least two of the blas*nreres at the 4 ~ 1
stage are totipotent. In the pig, single blastcleres of 2-8-cel1 stages
have been isolated and groan ~ vitro to the blasts cyst stage Adore et
al. 1969; Bonito & Wright 1983). Recently, several abstracts have
appeared indicating that up to 50% of half embryos at the morula to
blasts stage can regulate ad develop? into off~prir~ kilt as yet there
is ran proof that two halves of the Sam embryo have this capacity (Rorie
et al 1985; Naga~hima et al 1987~. In the goat, then is a report that
dins can develop halved blast~ysts (Iritani, 1987~.
31 Saunas: Fin this chat sketchy Picture of dares;tic arm
- ~ .
laboratory specked, it appears that the capacity for independent
development of a single blastomere ~ retained to a later stage ~
cleavage in rabbit, sheep and horse embryos than in the meet frequently
used model, the mc use. Survival of half embryos may be similar or better
in sheer and cows than in mace, and the survival of both halves or even
quarters to produce identical offspring has been ~~r-~==fu1 ~ domestic
species with significantly fewer attempts, indicating a greater regulative
capacity of partial embryos in these species compared with the mouse. The
cocurresce of blastulation at a later cleavage division and thus a higher
tctal ~11 number in some species, including humans, may allow greater
flexibility Embryonic organization. If ~ Is a critics Her of
ICM Ads—~~ which normal de~rel~nt of Me feds w~11 Scat mar,
embryos that blastula~ with a higher Gal ~1 1 nor arm thus a higher
proportion of ICM oe11s (Bubhr & Wren 1974) may be able to tolerate a
pr~portic~nat=ly greater crease ~ ~11 nuder. E—ever, We
relatic~ip bean cell red arm embryonic ~rzab;li~ reds to be
retain ~ test this idea, arm other factors such as later
determination of Specific ~11 lineages may also play an important role In
sp~ies Riffles.
- 308
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OCR for page 309
The avail able information from the=- and other types of manipulation
studies indicate= that mammalian embrycs share with the mn~c~ a
considerable flexible ity in regulative development and may also share
mechanisms of determination. It is important, however to critically
evaluate each species to avoid unwarranted extrapolation between species.
Cone red only r~r =~ exceptional animals ~ as the nit
armadillo, Sleigh regularly ~~ ~nozyga~s Pleas, to realize
what Salem but significant variations ~ Are cloudy related species
might well exist.
How is Regulation Accomplished?
1) Regulation in the early embryo: From the variation seen in the
experiments described above, it appears that regulation does nor always
~~' even ~ situations where the embryo or blast~re has the Bestial
to Pram its devel~nt. Ethnical factors affecting regulation, hcrw
c~xl~let~ly, hcrw quickly and thresh Hat Urania it is ached are
q~estims that nest be appruadhed experinent~lly. Does effective
regulation involve only oel1 ~ or Is embryo volume important? Is it
recopy that all tissues be recrated to the same Pro? these are
questions Hat bear By on Patios Hat are - plier] to Han
embryos arx] thus are a matter for urgent consideration. Wd have rectory
bed staying these questions using the Use as a ~de] art the folly
is a smrr~ry of unpublished work clone in oollabc ration with Dr. K.M.
and Dr. J.D. Diggers. We have Emil the recense of ache Use embryo
to a 50% reduction by destroying one blast~re at the Shell stage art
then following the development of ache resulting half embryos.
Tarl~ki (1959a, 1959b) fat that half embryos surviving until =}e
12th day of gestation had r~adhec] the sac stage of clevelc~rent as Errol
embryos arx] that ache birch weight of live young derived frae half embryos
was not significantly different. Other sties have pelvis eerie
Hat Use half embryos adjust to a~r~imat=1y normal size by the 7th day
of gestation (IŁ'wis & Rossant 1982~. In contrast, 18 day fetus ~ derived
frail half embryos have been shown to weigh significantly lace than those
fr=ul centrals (Tsuncda & MeLaren 1983~. Another study found that half
embryos produced by destruction of one blasts mere at the 2-cel1 stage
regulate the ~ size between 7.5 and 10.5 days of development although the
half embryos may became smaller than controls again by 13.5 days (Rends
l986~.
Our approach has been to examine the immediate results of halving
2-cell embryos on the formation of the blaseocyst and to correlate this
with developmental potential. We have exarinel the effects of ct:1ture in
vitro verses return of the embryos to the reproductive tract, and also
examined a surrc gate in viva environments the immature mouse oviduct' for
its ability to support c]mrelc~nt of half embryo;. Enbryo'; were first
recovery at the 2 cell stage, 1 blasters was destroyed by lyres, they
were Hen either alltu~d ~ vitro or transferred to F~c~r~nant or
immature oviducts for 2 days. Ebllc~nng recovery, they were aced for
mar p ology, art cell nu ~ an the It art trc = ~ todenn, art sane were
retransferred to one day asynchronous foster mothers to determine their
further developmental potential.
309 -
OCR for page 310
a) homology. In vie o culture results ~ a delay in Antic
Revels, but In Cur spry half embryos were at similar ~~Ic~i~1
yes as intact Dots, ir~icatir~ Cat ~rp~s of ye blast~st
am 10 dam ~ cast ~ (.~:lnith & local, 1977; Ferlla~ &
~zquie~, 1980~. 1~ was arid of a my hider He of
normal develc~rent In vitro than in vitro, although it ~ Legible that
a~ at dege~tirg Cargos were Are difficult to recover.
b) Sell Nlm~ ark Viability. Within ens Culture critical, C~11
camber ~ half embryo was approximately half that of controls as em
fraa our Aries ir~ica~cir~ bat upward ce1 1 Tn~ ruination A; rot
burr urIti1 after iT~pla}~tation crams 1986~. Our results indicate that
this relationship holds ureter a variety of ^~1~ oonditia~. men me
ribryo6 were transferred to fever mothers as ~ mat strict measure
of vibbili~r, it was fat bat cell Amber of the prei~plantatic~n ~ryc6
orated with viability and that half embryos Anal all culture
conditions had 1cher viability than controls (Figure 1~.
this does not present the whole picture, however. Figure 2 provides
a diffract representation which su~ivid - ; the reproductive 1~= ink
implantation failure as distinct frown failure to Revels after
implantation. Among the intact oontro1 embryos, the 106s in viability,
which ~ correlated with a lower cell number, can be seen to affect both
~= —= ~ _~ ~~ . ~ ~ = _ ~ ~ , _~ ~ =, ~ = _ .~ ~ ~ ~
=1 - mat: i~1~t nor I- 111= I~ 1 =tW~y~, Wl"1 A- W`~ly ~~
cell numbers and viability, however, present a different picture. The
proportion of failure due to postimplantatian MOP, i.e. failure to
develop normally after evocation of a dŁcidu~1 response, Increases
dramatically, indicating development of the trephecb4derm at the expense
_ . . . _ . . . . . . . . .
Of the inner cell mass. S. mce blastulation occurs at a particular time
regard of the number of cells, and since the proportion of inner cells
~ predicted to be lower in embryos of low ~11 number at the time of
blastulation, this result implicate= IoM ratio at that time as being a
calve factor in the lowered viability of these embryos.
c) ~ ~ Ratio. m e proportion of ICM cells to fetal cells was
determined for embryos of each group using a differential Eye method to
distinguish between ICM and trophectoderm (Handyside & Hinter 1984~. A
preli ~ comparison between half and control embryos for a given
culture condition fits with the prediction that embryos with lower call
rammer at the time of blastulation will have a lower ICM refill ratio and
also with the prediction that a lcm ICE ratio will Case viability.
Ibe results are ir~plete as yet he He irr3icatio~ are that In viva
creature, even in a nor~pregnant uterus, promotes the formation of a
relatively lance Im and that the Semite Is tree of in vice Cute
(V.E. E=aioa~u arm K.M. Exert, ur~liŁ~ data).
2) Effect of P~ulati~ on later DE`rel~nt: In a separate stay,
half embryos were pried in the sam way kilt were immediately
transfer to foster mothers arm allay ~ Replete their develc~nt to
- 310
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Form. The abject of this study was to assess phenotypic variation among
mice produced from half embryos and to compare them with genetically
identical mice developing from intact embryos. In other words, half
embryos were examined for evidence of a greater phenotypic variation that
might indicate incomplete of inconsistent regulation. In ablution to
intact control embryos that were recovered brow the mothers and
retransferred (transferred controls), an sectional ~ Itch was to compare
mice developing from unl isturbed pregnancies (controls).
a) Reproductive Success. Preimplantatian, fetal and neonatal losses
in the different groups of animals are indicated in Figure 3. The lower
Bar - -=S of pregnancy among recipients that received half embryos compared
with ~1 embryos argues in favor of a failure that is embryo-related
and is consistent with the results of the previous study. Implantation
failure and failure during gestation regild not be distinguished in this
study since implantation sites were not counted, but during gestation,
half embryos were again less s~-ssful than controls, and this indicates
a limitation to regulation.
An interesting finding was a higher neonatal mortality in mice that
developed from half embryos. It is known that neonatal 1~= is Aviated
with an increase in the duration of pregnancy and that the duration of
pregnancy is increased by small litter size (McLaren 3970~. In our study,
embryo transfer, regardless of the embryos transferred, resulted in ~mPd1
litters and the duration of pregnancy was increased in inverse proportion
to the litter size. Thus the increased neonatal loss can be explained as
an indirect reproductive effect and not as a reflection of a decreased
survival potential of mice developing frum half embryos.
b) Variation After Birth. A detailed analysis of phencLypic
variation among the surviving mice developing from half embryos is
underway VIE. Papaioanocu, J. Mkandawire & J. D. Biggers, unpublished
data). Preliminary results have shown little variation and no differences
that could be attributed to incomplete regulation. m e sex ratio among
c^,~=ls, transferred controls and half embryo mice was not significantly
different. Maturation events such as age at eye opening and age at
vaginal opening were similar for all three groups, as were growth curves
for body weight and tail length.
Although a number of measures have yet to be analyzed, it Appears
that complete regulation has taken place in all aspects of the anion by
the time of birth in mice developing from embryos halved at the 2-cel1
stage. The considerable variation seen among developing half embryos
Doris preimplantation and pcetimplantation develc~t, Ever, is an
irxtication that there are critical points or cream- In ~velc~oent that
serve to eliminate embryos that have not regulated. Implantation is
certainly one of these critical points since a failure here dcoms the
embryo. The narrow wiretap of Cal con patibility by barber arm
Euro for successful implantation Is a stringent rent for a
particular level of embryonic develc~nt so that development of furx~icn
- 311 -
OCR for page 312
my have Ken place by this thy even if cell Her ~ not z~a~.
Be timing of blast formation Is an indicatic~n Bat this Alar;
alff~a~h prei~plantatic~n 1~ associated with half Oryx; in alr Any
indicate Bat tsareti~res Be half embryo ~ ~;~l incurable of elici~cir~ a
denim ret.
If implantation is Awfully initial - , Be ralati~hip between
the Her of cells ~ the IN arc In the try: of the beastly
may present Adler critical devel~rtal poirrt. Alt~a~h it ~ rut
On whether scheme Is a minis Mary Her of IN ~Is, it Is
kr~ that these owls stimulate proliferation of the Arm
(Gabby et al 1973) Al that the entire as `~l as cone
excrae~ryonic Airy are derived fmn the IO1 (Papaioanr~u 1982). A
lo IN ~11 ~ at the time of blasts formation caUd create
problems at specific stagy (a threshold effect) or put ~rTibryo6 at a
~i~dvan~cage th~a~t develc~ent. Mbre ex~ri~cal work will ne—to
be done to further ill~nirmte the Manic of regulation, not only Be
Ablation of cell no, but also regulation In the pr~ortionof
clifferentiat~ cell type; arm regulation of furx~tion. Sway of ache forcer
acting on embryos to eliminate defective eribry~= or thy that have not
successfully regulated will provide insight into Educible i~pr~ver~nts in
t~niq~es for hartlling embryos of any species.
- 312.
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Transfer", C.E. Adams, Ed., CRC Press, Inc., coca Raton, Florida, pp
135-154.
Allen, W.R., and R.~. Pashen. 1984. Prc~uction of monozygotic (identical
horse twins by embryo m~cromanipulation. J. Reprcd. Fert.
71:607-613.
Brackett, B.G. 1978. Experimentation involving primate embryos. In: ' ~ thods
in Mammalian Reproduction", J.C. Daniel, Jr., Ed., Academic Press, Inc.,
New York/ Londonl S.F., pp. 333-357.
Buehr, M., and A. Mien. 1974. Size regulation in chimaeric mouse embryos.
J. Embryol. exp. Morph. 31:229-234.
Davis, J., and H. H-c~eldahI. 1971. ~ ative embryology of mammalian
blastocys~ . In: "The Biology of the Blastocyst", R.J. Blandau, Ed.,
University of Chicago Press, pp. 27-48.
Enders, A.C., and S. SchlafRe. 1981. Differentiation of the blastccyst of the
Rhesus Monkey. Am. J. Anat. 162:1-21.
Fernandez, M.S., and L. Izquierdo. 1980. Blastcac#1 formation in half and
double mcuse embryos. Anat. Embryol. 160:77-81.
Gardner, R.L. 1972. An investigation of inner cell mass and trophoblast
tissues following their isolation Frau the mouse blastocyst. J. Embryol.
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Gardner, R.L. 1974. Microsurgical approaches to the study of early mammalian
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Gardner, R.L., V.E. Papaioannou, and S.C. Barton. 1973. Origin of the
ectoplacenta~ cone and secondary giant calls in mouse blas*ocYsts
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exp. Morph. 30:561-572.
Gartner, K., and E. Baunack. 1981. Is the similarity of monozygotic twins due
to genetic factors alone? Nature 292:646-647.
Gatica, R., M.P. Boland, T.F. Crosby, and I. Gordon. 1984. Micromanipulation
of sheep morulae to produce monozygotic twins. Theriogenology 21:555-560.
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IRE 1: Curative call Numbers and Timing (Days Aster Fertilization) of Devel~ne
(Modified f~ Pa~ioar~ and At, 1986)
faction
Cleavage of Aruba_ _Blas~atic~n Entry
into
2c 8c UPS ~ C'ell uteri
(days] fdays) Days a no
no. trays) Days Stage ferenoeC
Story Sp~ies
louse 1 2 2.5 8-16 3 32 3
Rat 1.5 3.5 4.5 3.s
Rabbit 0. 5 1. 5 2 16-32 3 128 3
Tic Species
/
Pig 0.5-1 2-3 3.5 8-16 3.5-5 16 2.5-3
Shut 1 2 3 4 . 5 64 3
~ 1 2-4 4-5 ~ 6 5 - 6 3
Horse 1 3 4-5 >15 7-8 5-6
primate
. .
Rhesus lackey 1 2-3 >4 >26 by 7 4
8a~n 5 5-8 4-5
Hmnan 1.5-2.5 2,5_3b 3-5 16 4.5_5d 64-107 3-4
A:
a ES = early sanite; BC = blasts; 16 An
b
cr~n-runp 1er~.
In vitro.
1, Mayer and Fritz (1974); 2, Davis and ~~ldahl (1971); 3, perry and Relays
Parts (1982); 5, Willadsen (1980) ;, 6, Hamilton and Day (1945); Steven ark M
Heuser and Streetcar (1941); Imps am Harts (1941); Elixirs and S~laf1m (1981)
(1978) .
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OCR for page 318
DEBBIE 2: Percentage Noreen Develc~nt of Animated ~ Wry
Viable Fetucp" or Off~prir~ Modified thou Papaicx~ & Exert,
Sirgle
blast fen Half~bFy=; fmn ~ _
Pact
2c 4c 8c 4c 8-16c manila BC Sac 4c 8
Mouse 65 0 0 46 30 42 46 40 0
Rabbit 30 19 11
30
5h~ 52 16 6 100 80 58 31 >ob
~ — — ~ — 16 46 48 — —
Horse - 36
16
~E: Results fryers different sties are Wined (to text for ref~xs).
a Not ~e.
b 10 pairs of twins have in produced follawir~ freezing of one half of eat pear
c This figure represents only two twin pairs; (W;lladsen, 1980~.
- 318
-
Representative terms from entire chapter:
half embryo
