Re: Transfer of species nucleus into different species enucleated oocyte

Hello again, Michael!

You have proposed a very interesting experiment.  As was the case for your 
last question regarding interspecies embryo transfer, there is very little 
published information on interspecies nuclear transfer.

Nuclear transfer is a procedure in which the genetic material from a donor 
cell is transferred to the cytoplasm of a recipient cell whose genetic 
material has been removed.  This technique has received much attention 
recently because it is often used as a method for creating genetically 
identical clones of an organism.  When nuclear transfer is used in this 
context however, it usually involves donor and recipient cells from a 
single organism or from a single species.

The experiment you propose (injecting a monkey nucleus into an enucleated 
cow oocyte) is a challenging one.  Although I do not know for certain if it 
would work, I expect that it would not.  One reason is mitochondria.  
Mitochondria are highly specialized organelles that are responsible for 
providing the cell with energy.  Interestingly, these organelles are 
maternally inherited.  In other words, when fertilization occurs, it is the 
oocyte that contributes its mitochondria to the zygote, not the sperm.  In 
your experiment, a monkey nucleus would have to cooperate with cow 
mitochondria.  It is unlikely that this would happen; human mitochondria, 
for instance, cannot function properly in the presence of a mouse nucleus. 
 Furthermore, there are probably other important cytoplasmic factors 
contained in the cow oocyte that would not be able to operate normally when 
a "foreign" nucleus is present.  Unfortunately, we know little about the 
nuclear-cytoplasmic interactions that occur during nuclear transfer when 
the donor nucleus and recipient cytoplasm are of the same species, or even, 
the same organism, much less when they are of different species.    

Although the literature regarding interspecific nuclear transfer is sparse, 
I was able to find two articles.  One deals with the production of 
rat-mouse hybrid embryos using nuclear transplantation.  These scientists 
injected rat nuclei into mouse oocytes, placed the embryos into mouse 
foster mothers, and found that the resulting embryos arrested at very early 
stages of development (usually before the 5- to 8-cell stage).  From their 
experiments, they concluded that a rat nucleus is not capable of 
functioning properly in mouse cytoplasm.  The other article is written in 
Chinese, but the abstract is available in English.  These scientists 
studied nuclear transfers between mouse and rabbit.  Although I was not 
able to read any of their data or observations, they write in their 
abstract that they consider it possible to obtain normal early development 
of interspecies nuclear-cytoplasmic hybrid embryos between mouse and 
rabbit.  This is in contrast to the previous article which reported 
difficulties in making rat-mouse hybrids. However, it is not clear how long 
the mouse-rabbit hybrid embryos were able to develop and if they were able 
to give rise to healthy adults.  It is likely that the rules governing 
interspecies nuclear transfer are as complex as those for interspecies 
embryo transfer.  Furthermore, what works for one system (i.e. rat-mouse 
hybrids) may not necessarily apply to another (i.e. mouse-rabbit hybrids).

Here are the citations for the two articles I mentioned:

Waksmundzka, M; Journal of Experimental Zoology; 1994; 269(6):551-559

Mei, Q; Zou, XG; Du M; Shih Yen Sheng Wu Hsueh Pao; 1993; 26(4):389-97


I hope this information is helpful!  Please feel free to email me with 
further questions.

Nikki
nmdavis@fas.harvard.edu