This is a post I originally posted at the AoZ forum thing several years ago before I stopped going there, because for some reason TOR was getting blocked all the time.
Anywho, this is a copy I have of what I posted. There's long been a discussion about women getting pregnant from dogs. IDK why this keeps coming back up. It's simply not possible. The people who claim its possible or that it 'might' be possible always come up with anecdotes or some very very stretched reasoning to back up their position.
While there are many threads along the same lines as this, this is specifically intended to serve as a thread for scientific discussion on the issue. Hopefully we can put this claim to bed once and for-all.
I would ask one thing from any participants in this thread. If you are going to make a claim about something... provide a source. You don't have to source every sentence you make, but if you're relying on some principle to back up your claim, you better do your damn diligence and have something to back it up.
I went into this knowing that a successful synthesis of a human ovum and a canine sperm is not possible. But my curiosity lies in how far it can get -before- it fails. I have a BS in Biology and I'm working on my Masters right now. I dont know everything... I'll admit there's a lot I dont know, but I when I want to know something, I try to research it and learn it.
Ok... so without further ado... Here's the original post: (With some basic grammar and spelling corrections)
The Science of Canine Male + Human Female gamete interactions
A look into the cellular mechanics behind canine sperm and human egg interactions.
Warning: Nerd alert - this is very science-y
Disclaimer: I'm a bio major and This has sort of been a pet research project for me for the past couple years. I have posted this elsewhere before, but I'm not sure how many places its been repeated. But lets get one thing crystal clear. It is impossible for a human to get pregnant by a dog. Anyone claiming otherwise is either outright lying or an idiot. It's definitely a fantasy of mine, not going to lie, but its 100% impossible.
Others will claim that the human egg and canine sperm will fuse and the single cell will live a few days before dying. This is also 100% impossible and a total lie. Due to chromosomal mismatch, a complete DNA strand cannot form, thus no viable living single cell at all.
My main point of researching this was to see if Canine sperm will do anything with the egg at all. If the proteins are not right the sperm will just wiggle around and try to do their thing. I'm curious if the sperm will chemically try to bond with the egg and breach the egg cell wall and try (and fail) to fuse with the egg nucleus. This is unknown and I haven't been able to find the necessary information to see if this can happen. Most likely there isn't enough research out there in the differences between all the human/canine proteins to know... so I'd need to actually take some canine sperm and a human egg and try artificial insemination and use an electron microscope to see what happens. But lets be real... that's never going to get approved at my university so I'm not even going to bother to ask. lol
Anywho, lets get on with this... by starting with how it works in a HS/HS situation:
Between humans, spermatozoa and oocyte fusion in the membrane adhesion area requires the presence of 3 membrane proteins (spermatozoa IZUMO1; oocyte receptor Juno and Cd9). The first one being the important one on the spermatozoa side, the latter on the oocyte side.
That would proceed as shown in the article image Source here:
Image is missing, because of the repost
In Humans this ultimately leads to the formation of a zygote pronuclei as the Male and Female haploid nuclei approach each other and nuclear membranes break down.
After this then the DNA starts to bond together and divide into a multi cell blastocyst. If everything goes well this all happens within the first 24 hours.
So what would actually happen here biologically if it were K9 spermatozoa / HS oocyte? It’s obvious that a human female cannot get pregnant by a canine… but a canine’s spermatozoa don’t know where they are. Would Oocyte Activation ever occur and the intracellular machinery of the oocyte would try to process the DNA of the spermatozoa cell or not?
I assume the spermatozoa would attempt to fertilize the oocyte. With humans the spermatozoa have to sort of burrow their way in and then bond with the egg with certain proteins. Would canine spermatozoa be able to bind with the external layer of a human oocyte and attempt to fertilize the oocyte? That's what I want to determine.
This is the first question; would the k9 spermatozoa actually fuse with the oocyte? If it can’t then the rest of the discussion is pointless, but if it does, things are at least one step further down the path before failure. As I sated above, in humans it is the IZUMO1 protein that is important on the spermatozoa side. For more than obvious reasons I was unable to find any research into if the spermatozoa Human zona pellucida protein (ZP2) would effectively be a reciptor for the K9 spermatozoa. If Human ZP2 does not receive the k9 spermatozoa, then membrane fusion cannot occur.
I did find the following on page 317 tonight while reading
https://books.google.com.ua/books?id=95XqDQAAQBAJprintsec=frontcover#v=onepageqf=false
It states that Dogs have a Izoumo1R gene, and that it’s located in a similar location as human spermatozoa. It states that it its plausible but untested that the purpose of IZUMO1 and JUNO in canines allows the spermatozoa to fuse with oocytes during fertilization like it does in Humans. Sadly the google books preview I found doesn’t have the pages surrounding that to get the rest of the context.
I have not yet found the breakdown of the differences in the IZUMO1 gene and the protein it codes for in Humans and the IZUMO1R gene in Canines. So this is where I will be focusing first. I’m not sure how much research has gone into Canine reproduction, so there may be no answers.
However, lets make sure we dont lose our grasp on reality, even if Oocyte activation is possible, a Canine/Human hybrid is not possible.
There is no way the embryo should be able to develop, since there is no way that the DNA could match up. Humans have 23 pairs of chromosomes, while Canines have 39. There is no way that the DNA would be able to be spliced together enough to create a viable cell that could even start to divide. By day 2 a properly fertilized oocyte is already a multi-cell blastocyst. Since Human and K9 DNA is not compatible, there is no way that it could reach this phase.
Binding of mammalian spermatozoa to the zona pellucida and the induction of the acrosome reaction are prerequisites for successful oocyte fertilization. The human oocyte coat, zona pellucida (ZP), is composed of four glycoproteins designated as zona pellucida glycoprotein (ZP1, ZP2, ZP, and ZP4) respectively. The zona proteins possess the archetypal ‘ZP domain’, a signature domain comprised of approximately 260 amino acid (aa) residues.
Mice which are used as the initial basis for fertitlity research for humans have 3 glycoproteins (ZP1, ZP2, and ZP3). The reason mice are used is that the similiarity in fertilization is very similar.
I have not seen much research into Canine/Human similarities, but I have found Canine/Mouse research.
We also know that canines are similar to Mice in that they have 3 glycoproteins, but they are (ZP2, ZP3, and ZP4. And research points to them having the same roles. Source:
https://www.ncbi.nlm.nih.gov/pubmed/9361810
Anti-ZP3 vaccine for canines which reduces fertility in canines, has been shown to reduce fertility in mice. This suggests that ZP3 responsibility is similar between canines and mice. Source:
https://www.ncbi.nlm.nih.gov/pubmed/27667457
Since we already know that ZP3 in humans is similar to ZP3 in mice we can ~assume~ that there are similarities between Human and Canine CP3. This may in fact be false. Example is the following sets: {0,1}, {1,2}, {2,3} The 1st and 2nd set are similar, and the 2nd and 3rd are similar, however the 1st and 3rd are not. So they may be similiar or they may not be. I have yet to find enough research to prove this one way or the other.
When I search the Protein Data Bank,
http://www.rcsb.org/pdb/explore/explore.do
I do find distinctions for ZP2 in mice, however for ZP3, all I find is “mammalian spermatozoa receptor ZP3”, I do not find any species specific ZP3 proteins. I have read in other research papers about the similarity of Human/Mouse ZP3, so this may be why there is not species specific protein data. However this does not mean that they are similar, it may mean that focused research has not been submitted on the specific species. Once again, the research is scant on the topic. Lack of evidence is not evidence of lacking.
There is some research pointing to the role of ZP1 in humans, but it’s not well studied. Studies suggest that the ‘ZP domain’ module of human ZP1 has functional activity and may have a role during fertilization in humans, but it’s extent is not known. Source:
https://www.ncbi.nlm.nih.gov/pubmed/20831819
However in Humans, while all the ZP glycoproteins are responsible in some way for spermatozoa/ooctye fusion, the primary role is ZP2. In mice, this is somewhat different. In the mouse, ZP1 is the homodimeric filament crosslinker, held together by intermolecular disulphides. ZP2 is the ‘secondary receptor’, which is cleaved by oocyte proteases after oocyte activation. The mouse ZP3 protein appears to be the ‘primary receptor’, which is responsible for species-specific binding of spermatozoa to the oocyte and the induction of the acrosome reaction. Source:
https://www.ncbi.nlm.nih.gov/pubmed/10526650
Information about ZP2 in mice:
Crystal structure of the ZP-N1 domain of mouse spermatozoa receptor ZP2:
http://www.rcsb.org/pdb/explore/explore.do?structureId=5II6
Crystal structure of the ZP-C domain of mouse ZP2:
http://www.rcsb.org/pdb/explore/explore.do?structureId=5BUP
With respect to Canines, Anti-ZP3 vaccine reduces fertility in canines, has been shown to reduce fertility in mice. This suggests that ZP3 responsibility in oocyte bonding is similar between canines and mice. Source:
https://www.ncbi.nlm.nih.gov/pubmed/27667457
If things weren’t already confusing enough, it’s about to get worse. There has been research between Human spermatozoa and Mice Oocytes.
Esto se ha logrado utilizando proteínas de la zona humana nativas/recombinantes purificadas y ratones transgénicos que expresan glicoproteínas ZP humanas. El modelo propuesto en ratones de la glicoproteína-3 ZP (ZP3) que actúa como receptor primario de espermatozoides y la glicoproteína-2 ZP (ZP2) como receptor secundario de espermatozoides se ha modificado para la unión de espermatozoides/ovocitos en humanos. Se ha demostrado que la glicoproteína-1 ZP (ZP1), la ZP3 y la glicoproteína-4 ZP (ZP4) se unen a los espermatozoides humanos capacitados. La ZP2 se une a los espermatozoides humanos que han reaccionado en el acrosoma. Además, los óvulos obtenidos de ratones transgénicos que expresan ZP2 humana sola o junto con otras proteínas de la zona humanas en lugar de las de ratón mostraron unión a espermatozoides humanos, lo que sugiere que la ZP2 también podría desempeñar un papel en la unión de espermatozoides/ovocitos. Esta función se ha mapeado a un dominio correspondiente a los residuos de aminoácidos 51-144 de ZP2.
Aquí está el punto clave: “A diferencia de los ratones, donde ZP3 es el agonista principal para inducir la reacción acrosómica, en los humanos, la reacción acrosómica puede ser mediada por ZP1, ZP3 y ZP4”. Fuente:
https://www.ncbi.nlm.nih.gov/pubmed/25445843
Así, la unión de los espermatozoides en los humanos se produce por todas las proteínas zpa, y sabemos que los caninos comparten tres glicoproteínas entre sí (aunque de forma algo diferente debido a la expresión genética).
Hasta ahora me he centrado en el aspecto de los ovocitos, pero uno de estos días intentaré centrarme en el tamaño de los espermatozoides pronto.
He oído una afirmación sobre las proteínas que cubren el ovocito y que determinan qué espermatozoides se fusionarán y lucharán contra otros espermatozoides; pero nunca he visto que esto esté respaldado por una investigación. Sí, hay una capa de proteína alrededor del ovocito, a la que los espermatozoides tienen que unirse y atravesar. Pero no tendría sentido que los ovocitos femeninos evolucionaran para saber cómo lidiar con los espermatozoides de otras especies. Como mucho (por lo que he encontrado), los espermatozoides no se unirían a la zona pelúcida y, en cambio, seguirían intentándolo y fallarían. (Pobrecitos). Pero esto sucede todo el tiempo, los espermatozoides son las cosas más inteligentes del libro, simplemente nadan hasta que chocan con algo y luego siguen chocando hasta que finalmente se unen a algo.
Además de la afirmación del "ovocito inteligente", ya he leído en internet que el ovocito tiene un sistema inmunitario que "ataca" al espermatozoide hostil. Nunca he leído nada al respecto. Lo que sí he leído es que el aparato reproductor femenino en general puede mostrar preferencia por un espermatozoide sobre otro, como se describe en:
https://academic.oup.com/beheco/article/10/3/304/201626
Se han realizado algunas investigaciones sobre la selección de espermatozoides que muestran un sesgo anticonsanguíneo en otros animales. Fuente:
http://onlinelibrary.wiley.com/doi/10.1111/jeb.12545/abstract
Pero de nuevo, no he encontrado ninguna investigación que afirme que los ovocitos puedan determinar la especie de espermatozoides y atacar a los no compatibles.
Un poco relacionado…
Recuento de espermatozoides en caninos:
Total de espermatozoides/eyaculado: Un mínimo de 10 millones/espermatozoide/libra de peso corporal (es decir, un perro de 14 kg tendrá al menos 300 millones de espermatozoides). La mayoría de los perros normales superan estas cifras en 2 o 3 veces o más.
Fuente:
http://www.akcchf.org/educational-r.../Canine-Semen-Evaluation-Dr-Cheryl-Lopate.pdf
Recuento de espermatozoides en humanos:
El recuento de espermatozoides en un análisis de semen normal debe estar entre 20 millones y más de 200 millones.
Fuente:
https://www.healthline.com/health/semen-analysis#normal-results
Información adicional que surgió en una discusión posterior en otro hilo en el que publiqué esto:
Hay quienes afirman que la zona pelúcida humana y canina es prácticamente la misma. Nadie ha proporcionado fuentes que lo respalden. Si existen, me interesaría verlas.
Algunas personas afirman que se formará un grupo de células, pero que finalmente fracasará. Esto no puede ser cierto. La síntesis de DHA humano y canino no funcionará.
Los caninos tienen unos 19.000 genes codificados en su ADN, en comparación con los 30.000 de los humanos.
De los 19.000 genes caninos reportados, 14.200 representan ortólogos 1-1-1 entre perros, humanos y ratones. Fuente:
https://genome.cshlp.org/content/15/12/1706.full.html
No se obtendrá una célula viable si no se pueden formar tantos genes debido a problemas.
Si bien el mestizaje es posible en el reino animal, solo es posible cuando las especies son lo suficientemente parecidas. Un ejemplo de esto son los caballos, los burros y las cebras. Son tan cercanos genéticamente que pueden cruzarse. Los humanos y los perros no.
Algunos afirmarán que el factor Rh en la sangre es la razón de su fracaso. Siempre pensé que era un argumento ingenioso. No tiene sentido siquiera mencionar el factor Rh, salvo para parecer inteligente y científico. El factor Rh es irrelevante en esta situación, ya que solo es relevante cuando se trata de la mezcla de tipos sanguíneos. Eso requeriría que la implantación uterina se produzca y sea viable. Si no se produce la implantación, no se puede desarrollar la placenta. Si no se desarrolla la placenta, no puede haber mezcla de tipos sanguíneos. Si no hay mezcla de tipos sanguíneos, el factor Rh es irrelevante.
