Survival of the females

December 18, 2012

Because of the process involved in the formation of sperm cells, there should be an equal chance that a mammalian egg will be fertilized by "male" sperm, carrying a Y chromosome, as by a "female" sperm, carrying an X chromosome. The symmetry of the system ensures that roughly the same number of males and females are born, which is clearly helpful for the species' long-term survival.

Surprisingly, though, many mammals do not produce equal numbers of male and female offspring. The discrepancy could theoretically be explained by differential fertilization efficiencies of male and female sperm (Y chromosomes are smaller than X chromosomes so perhaps male sperm can swim faster?) or by different rates of survival of male and female foetuses in the uterus. Indeed, it does seem as though male embryos are better able to survive under conditions of high energy intake. But how does this work?

Jana Beckelmann in Christine Aurich's laboratory at the University of Veterinary Medicine, Vienna now presents provocative evidence that a particular protein, insulin-like growth factor-1 or IGF1, might somehow be involved. From an examination of about 30 embryos, Beckelmann noticed that during early pregnancy (between eight and twelve days after fertilization) the level of messenger RNA encoding IGF1 was approximately twice as high in female embryos as in male embryos.

The difference could relate to the fact that female embryos have two X chromosomes, which might produce more of a factor required for the expression of the IGF1 gene (which is not encoded on the X chromosome) than the single X chromosome in males is able to generate. Beckelmann was also able to confirm that the IGF1 protein was present in the embryos, confirming that the messenger RNA is actually translated to protein.

IGF1 is known to have important functions in growth and to inhibit apoptosis, or programmed cell death. As IGF1 treatment of cattle embryos produced in vivo improves their survival, it is likely that the factor has positive effects on the development of the early embryo in the horse. So why should female embryos contain more of the factor than males?

Losses in early pregnancy are unusually high in the horse and it is believed that female embryos are especially prone to spontaneous abortion. Male embryos are known to be better able to survive under high glucose concentrations, so well-nourished mares preferentially give birth to male foals.

As Beckelmann says, "We think the higher IGF1 concentrations in female embryos might represent a mechanism to ensure the survival of the embryos under conditions that would otherwise strongly favour males." If this is so, the ratio of the sexes in horses is the result of a subtle interplay between environmental and internal factors, including insulin-like growth factor-1.
-end-
The paper "Sex-dependent insulin like growth factor-1 expression in preattachment equine embryos" by Jana Beckelmann, Sven Budik, Magdalena Helmreich, Franziska Palm, Ingrid Walter and Christine Aurich is published online in the journal "Theriogenology" and will be published in print in the journal's January 1, 2013 issue (Volume 79, Issue 1, 1 January 2013, pp. 193-199).

Abstract of the scientific article online (full text for a fee or with a subscription): http://dx.doi.org/10.1016/j.theriogenology.2012.10.004

About the Vienna University of Veterinary Medicine

The University of Veterinary Medicine, Vienna is the only academic and research institution in Austria that focuses on the veterinary sciences. About 1000 employees and 2300 students work on the campus in the north of Vienna, which also houses the animal hospital and various spin-off-companies.

http://www.vetmeduni.ac.at

Scientific contact:

Prof. Christine Aurich
Equine Clinic
University of Veterinary Medicine, Vienna
christine.aurich@vetmeduni.ac.at
T +43 664-60257-6400

Distributed by:

Klaus Wassermann
Public Relations/Science Communication
University of Veterinary Medicine, Vienna
klaus.wassermann@vetmeduni.ac.at
T +43 1 25077-1153

University of Veterinary Medicine -- Vienna

Related Chromosomes Articles from Brightsurf:

Cancer's dangerous renovations to our chromosomes revealed
Cancer remodels the architecture of our chromosomes so the disease can take hold and spread, new research reveals.

Y chromosomes of Neandertals and Denisovans now sequenced
An international research team led by Martin Petr and Janet Kelso of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, has determined Y chromosome sequences of three Neandertals and two Denisovans.

Female chromosomes offer resilience to Alzheimer's
Women live longer than men with Alzheimer's because their sex chromosomes give them genetic protection from the ravages of the disease.

New protein complex gets chromosomes sorted
Researchers from the University of Tsukuba have identified a novel protein complex that regulates Aurora B localization to ensure that chromosomes are correctly separated during cell division.

Breaking up is hard to do (especially for sex chromosomes)
A team of scientists at the Sloan Kettering Institute has discovered how the X and Y chromosomes find one another, break, and recombine during meiosis even though they have little in common.

Exchange of arms between chromosomes using molecular scissors
The CRISPR/Cas molecular scissors work like a fine surgical instrument and can be used to modify genetic information in plants.

How small chromosomes compete with big ones for a cell's attention
Scientists at the Sloan Kettering Institute have solved the puzzle of how small chromosomes ensure that they aren't skipped over during meiosis, the process that makes sperm and egg.

GPS for chromosomes: Reorganization of the genome during development
The spatial arrangement of genetic material within the cell nucleus plays an important role in the development of an organism.

Extra chromosomes in cancers can be good or bad
Extra copies of chromosomes are typical in cancerous tumor cells, but researchers taking a closer look find that some extra copies promote cancer growth while others actually inhibit cancer metastasis.

X marks the spot: recombination in structurally distinct chromosomes
A recent study from the laboratory of Stowers Investigator Scott Hawley, PhD, has revealed more details about how the synaptonemal complex performs its job, including some surprising subtleties in function.

Read More: Chromosomes News and Chromosomes Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.