The Maternal Effect

 
The effect was first discovered in the 1930's with snails. With any given species, the spiral of the shell may be left-handed or right-handed. It seemed to be inherited in a Mendelian fashion, except the ratios were skewed. In fact the handedness of an individual snail was always the same as the mother's. Any change only showed up at the next generation. It would seem that snail handedness is determined by the maternal DNA, before the snail's own DNA has kicked in.

The phenomenon was further studied in fruit flies (what else!) and was found to determine four fundamental features in development

It seems to be important for correct development for all animals, although there appears to be little in the literature, especially for humans.

"A protein known as heat-shock factor-1 (HSF1) is a major transactivator of stress-inducible genes in response to environmental changes, but it is also implicated in extra-embryonic development and female fertility in mice. . . . . mouse embryos whose mothers lack this protein are unable to develop properly beyond the zygotic stage, although oocytes were ovulated and fertilized normally."; The females concerned were mated with so-called "wild-type" males whose genes would be expected to be dominant to defective genes in the mother. Since they did not prevent the problem with the female's zygotes, it indicated it was caused by a 'maternal effect' mutation. That is to say, "HSF1 from the mother [rather than the zygotes own DNA] normally controls early post-fertilization development."⁽¹⁾

In another recent study,⁽²⁾ a gene called Mater, dependent on the maternal genome, was shown to be essential for embryonic development beyond the two-cell stage. It was shown to to be a maternal gene, because females lacking it are sterile, while null males are fertile.

We have, however, found one human study,⁽³⁾ to do with sickle cell anemia and beta thallassemia. The genes responsible are recessive, and those who have both copies (are homozygous) experience severe problems. However, being heterozygous for the genes confers resistance to malaria, thus in a malaria-rich environment one would expect heterozygosity to predominate among the adult population.

The study looked at babies born to couples where one partner was heterozygous, while the other was homozygous. The Mendelian ratio of heterozygotes born to heterozygous mothers with homozygous fathers was higher than the other way round. The suggestion was that the maternal effect favoured the transmission of the sickle cell and beta-thalassemia alleles.

Footnote

Do not confuse this with mitochondrial DNA which we discuss next

Bibliography

1. E. Christian, A. A. Davis, S. D. Thomas, I. J. Benjamin, (2000) Embryonic development: Maternal effect of Hsf1 on reproductive success (Absract) Nature 407, 693 - 694 (2000); doi:10.1038/35037669
2. Zhi-Bin Tong, Lyn Gold, Karl E. Pfeifer, Heidi Dorward, Eric Lee, Carolyn A. Bondy, Jurrien Dean, Lawrence M. Nelson, () Mater, a maternal effect gene required for early embryonic development in mice (Abstract) Nature Genetics, doi:10.1038/81547, volume 26 no. 3 pp 267 - 268
3. Duchovni-Silva I, Ramalho AS.(2003) Maternal effect: an additional mechanism maintaining balanced polymorphisms of haemoglobinopathies? (Abstract) Ann Hum Genet. 2003 Nov;67(Pt 6):538-42

NEXT Mitochondria