Genetic Imprinting

No parthenogenesis in mammals

Genomic imprinting and the strange case of the insulin-like growth factor II receptor .

Haig D, Graham C. Cell. 64:1045-6 (1991)

Maternal-Paternal Conflict Theory

The sins of the fathers and mothers: genomic imprinting

in mammalian development. Tilghman SM. Cell;96:185-93 (1999).

A growth-deficiency phenotype in heterozygous mice carrying an

insulin-like growth factor II gene disrupted by targeting. DeChiara TM, Efstratiadis A, Robertson EJ.

Nature. 1990, 345,78-80.

Loss of the imprinted IGF2/cation-independent mannose 6-phosphate receptor results in fetal overgrowth

and perinatal lethality. Lau MM… Stewart CL.

Genes Dev. 1994 ;8, 2953-63..

Rescue of the T-associated maternal effect in mice carrying null mutations in Igf-2 and Igf2r, two reciprocally imprinted genes.

Filson AJ, Louvi A, Efstratiadis A, Robertson EJ Development. 1993, 118 :731-6.

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Holmes: “When you have eliminated the impossible, whatever remains, however improbable, must be the truth”

“Perhaps,” said Watson, skeptically, “You may have convinced me as to the motive, but you are yet to explain how it is done.”

Tilghman SM. Cell 1999 ;96:185-93

A maternal-offspring coadaptation theory for the evolution of genomic imprinting.

Wolf JB, Hager R. PLoS Biol. 2006 Nov;4(12):e380.

Imprinted genes are expressed either from the maternally or paternally inherited copy only, and they play a key role in regulating complex biological processes,

including offspring development and mother-offspring interactions. There areseveral competing theories attempting to explain the evolutionary origin of this

monoallelic pattern of gene expression, but a prevailing view has emerged thatholds that genomic imprinting is a consequence of conflict between maternal andpaternal gene copies over maternal investment. However, many imprinting patterns

and the apparent overabundance of maternally expressed genes remain unexplainedand may be incompatible with current theory. Here we demonstrate that soleexpression of maternal gene copies is favored by natural selection because itincreases the adaptive integration of offspring and maternal genomes, leading to

higher offspring fitness. This novel coadaptation theory for the evolution ofgenomic imprinting is consistent with results of recent studies on epigeneticeffects, and it provides a testable hypothesis for the origin of previouslyunexplained major imprinting patterns across different taxa. In conjunction with existing hypotheses, our results suggest that imprinting may have evolved due to

different selective pressures at different loci.

Imprinted genes, defined by their preferential expression of a single parentalallele, represent a subset of the mammalian genome and often have key roles inembryonic development, but also postnatal functions including energy homeostasis and behaviour. When the two parental alleles are unequally represented within asocial group (when there is sex bias in dispersal and/or variance in reproductivesuccess), imprinted genes may evolve to modulate social behaviour, although sofar no such instance is known. Predominantly expressed from the maternal alleleduring embryogenesis, Grb10 encodes an intracellular adaptor protein that caninteract with several receptor tyrosine kinases and downstream signallingmolecules. Here we demonstrate that within the brain Grb10 is expressed from the paternal allele from fetal life into adulthood and that ablation of thisexpression engenders increased social dominance specifically among other aspects of social behaviour, a finding supported by the observed increase in allogroomingby paternal Grb10-deficient animals. Grb10 is, therefore, the first example of animprinted gene that regulates social behaviour. It is also currently alone inexhibiting imprinted expression from each of the parental alleles in atissue-specific manner, as loss of the peripherally expressed maternal alleleleads to significant fetal and placental overgrowth. Thus Grb10 is, so far, aunique imprinted gene, able to influence distinct physiological processes, fetal growth and adult behaviour, owing to actions of the two parental alleles indifferent tissues.

Distinct physiological and behavioural functions for parental alleles of imprinted Grb10 .

Garfield AS…Ward A. Nature. 469(7331):534-8 (2011)

High-frequency generation of viable mice from engineered bi-maternal embryosManabu Kawahara….& Tomohiro Kono. Nat Biotechnol. 25:1045-50 (2007)

Mammalian development to adulthood typically requires both maternal and paternal genomes ,because genomic imprinting places stringent limitations on mammalian development, strictly precluding parthenogenesis. Here we report the generation of bi-maternal embryos that develop at a high success rate equivalent to the rate obtained with in vitro fertilization of normal embryos .These bi-maternal mice developed into viable and fertile female adults. The bi-maternal embryos ,

distinct from parthenogenetic or gynogenetic conceptuses, were produced by the construction of oocytes from fully grown oocytes and nongrowing oocytes that contain double deletions in the H19 differentially methylated region (DMR) and the Dlk1-Dio3 intergenic germline–derived DMR. The results provide conclusive evidence that imprinted genes regulated by these two paternally methylated imprinting-control regions are the only paternal barrier that prevents the normal development of bi-maternal mouse fetuses to term.

Amniotes

Biology (Kampbell & reece)

Early mammalian development

http://universe-review.ca/R10-33-anatomy.htm

Amniotic development- reptiles and mammalsOviparous versus viviparous

Dizygotic twins

(fraternal or non-identical twins)

Monozygotic twins

(identical twins)

<5 days

5-9 days

>9 days

Do monochorionic dizygotic twins increase after pregnancy by assisted reproductive technology? Miura K, Niikawa N. J Hum Genet.;50:1-6 (2005).

Blood group chimerism in human multiple births is not rare.

van Dijk BA, Boomsma DI, de Man AJ. Am J Med Genet. 61:264-8. (1996).

Twin blood group chimerism seems to be very rare in humans. The 30-40 previously reported cases usually were found by mere coincidence during routine blood grouping in hospitals or

blood banks. Usually in these cases frank blood group mixtures of, for example, 50/50%, 25/75%, or 5/95% at most were seen. Smaller percentages are very difficult to notice during routine work-up. Using a sensitive fluorescence technique (sensitivity > 0.01%) we detected blood group chimerism in 32/415 (8%) twin pairs and 12/57 (21%) triplet pairs, respectively,

which is a higher incidence than reported previously.

יונקי ביבMonotremata

Marsupials -יונקי הכיס

Eutherians יונקי השליה

העץ הפילוגנטי המשוער של היונקים

Monotreme

Biology (Solomon, Berg & Martin) Life

קיפודן ברווזן

"Monotremes oviparous, ovum meroblastic" (Caldwell, September 2, 1884)

Marsupials- יונקי הכיס

Biology (Solomon, Berg & Martin)

Koala

Tasmanian wolf/tiger

From: Manipulating the Mouse Embryo. Hogan et al., Cold Spring Harbor Laboratory Press, 2nd Edition, 1994.

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The first developmental decision: ICM or trophoblast

The first developmental decision: ICM or trophoblast

Dev Biol 9th Ed. (2010)

Trophoblast ICM

The first developmental decision: ICM or trophoblast

Dev Biol 9th Ed. (2010)

From: Manipulating the Mouse Embryo. Hogan et al., Cold Spring Harbor Laboratory Press, 2nd Edition, 1994.

Fazleabas and Kim (2003). What Makes an Embryo Stick ? Science 299:355-6.

ליאונרדו דה וינצ'יעובר ברחם

1510~