Developmental Biology

fgf8 mRNA decay establishes a gradient that couples axial elongation to patterning in the vertebrate embryo. Dubrulle, J. & Pourquié, O. Nature 427, 419–422 (2004)

Axial development in vertebrate embryos proceeds in a stereotypical manner whereby cells differentiate according to their position in a protein gradient. This paper shows how the Fgf8 gradient that controls this process might form in the chick. fgf8 is transcribed only in tail-bud cells but this process stops as these cells move anteriorly during development. The protein gradient is consequently formed as the cells' supply of mRNA dwindles, therefore providing the answer to a long-standing question.

Population Genetics

Evidence for extensive transmission distortion in the human genome. Zöllner, S. et al. Am. J. Hum. Genet. 74, 62–72 (2004)

Mendel's laws predict that a diploid organism should transmit each chromosome at a similar frequency. Deviations from this 1:1 ratio — known as segregation distortion — occur in many species and for various reasons. By examining genome data from 148 families, the authors conclude that segregation distortion is extensive in humans and that many loci underlie this effect.

Gene Regulation

A noncoding RNA is required for the repression of RNApolII-dependent transcription in primordial germ cells. Martinho, R. G. et al. Curr. Biol. 14, 159–165 (2004)

Unlike somatic cells, primordial germ cells (PGCs) — those that will develop into eggs and sperm — need to remain undifferentiated: they are thought to do so by inhibiting RNApolII transcription. Ruth Lehmann's group has now found that a non-coding RNA that is encoded by the polar granule component (pgc) gene blocks RNApolII activity in PGCs, possibly by preventing transcription-activating enzymes from reaching the nucleus.

Medical Genetics

Molecular and comparative genetics of mental retardation. Inlow, J. K. & Restifo, L. L. Genetics (in the press)

Mental retardation (MR) is a common and genetically heterogeneous form of cognitive impairment. Jennifer Inlow and Linda Restifo estimate there to be hundreds of MR genes, 282 of which they have identified by data mining the Online Mendelian Inheritence in Man (OMIM) database and the literature. A total of 76% of these genes have functional orthologues in Drosophila, which indicates that this fly could be the ideal model to use to dissect the genetic basis of MR.