RNA Interference

MicroRNAs and small interfering RNAs can inhibit mRNA expression by similar mechanisms. Zeng, Y. et al. Proc. Natl Acad. Sci. USA 100, 9779–9784 (2003)

Evidence from plants indicates that small interfering RNAs (siRNAs) and microRNAs (miRNAs) are functionally interchangeable, although this is not the case in worms. The authors show that in human cultured cells, as in plants, endogenous miRNAs can inhibit the expression of fully complementary RNAs, and that siRNAs can do the same to RNAs with some mismatch. They propose that the siRNA and miRNA mechanisms of action might be interchangeable, depending on the level of target complementarity.

Developmental Genetics

The gene csd is the primary signal for sexual development in the honeybee and encodes an SR-type protein. Beye, M. et al. Cell 114, 419–429 (2003)

Twenty percent of animal species are haplodiploid, but the genes that are involved in this sex-determination system largely remain a mystery. Now, the honeybee sex-determining gene csd has been identified, positionally cloned and characterized. csd encodes a short (385 amino acid) protein with highly divergent alleles, as predicted for a sex-determining gene. RNAi knockdown of csd caused females to develop as male larvae, which confirmed the key role of csd.

Epigenetics

Transposable elements: targets for early nutritional effects on epigenetic gene regulation. Waterland, M. & Jirtle, R. J. Mol. Cell. Biol. 23, 5293–5300 (2003)

Our early diet could affect our susceptibility to chronic adult diseases by influencing DNA methylation. By supplementing the diet of mice with a phenotype that depends on the methylation status of a specific transposable element, Waterland and Jirtle were able to increase CpG methylation of the element and change the phenotype of the offspring. So, nutrition can affect epigenetic gene regulation through metastable alleles that are associated with transposable elements.

Human Genetics

Human handedness and scalp hair-whorl direction develop from a common genetic mechanism. Klar, A. J. S. Genetics 165, 269–276 (2003)

The genetic basis of human handedness remains elusive despite extensive studies. It continues to be one of the last clear-cut battlegrounds between the polarized advocates of 'nature' and 'nurture'. Amar Klar attacked the problem obliquely by showing that there is an association between handedness and an asymmetric trait that is unaffected by cultural influences: scalp hair-whorl direction. His data clearly support a simple Mendelian genetic explanation for handedness.