Irf6 is a key determinant of the keratinocyte proliferation-differentiation switch

The epidermis is a highly organized structure, the integrity of which is central to the protection of an organism. Development and subsequent maintenance of this tissue depends critically on the intricate balance between proliferation and differentiation of a resident stem cell population; however, the signals controlling the proliferation-differentiation switch in vivo remain elusive. Here, we show that mice carrying a homozygous missense mutation in interferon regulatory factor 6 (Irf6), the homolog of the gene mutated in the human congenital disorders Van der Woude syndrome and popliteal pterygium syndrome, have a hyperproliferative epidermis that fails to undergo terminal differentiation, resulting in soft tissue fusions. We further demonstrate that mice that are compound heterozygotes for mutations in Irf6 and the gene encoding the cell cycle regulator protein stratifin (Sfn; also known as 14-3-3sigma) show similar defects of keratinizing epithelia. Our results indicate that Irf6 is a key determinant of the keratinocyte proliferation-differentiation switch and that Irf6 and Sfn interact genetically in this process.     

The semenogelins: proteins with functions beyond reproduction?

The coagulum proteins of human semen, semenogelins I and II, are secreted in abundance by the seminal vesicles. Their function in reproduction is poorly understood as they are rapidly degraded in ejaculated semen. However, more recent results indicate that it is time to put the semenogelins in a broader physiological perspective that goes beyond reproduction and fertility. Received 21 June 2006; received after revision 16 August 2006; accepted 28 September 2006     

Sialic acid-specific lectins: occurrence, specificity and function

Sialic acids consist of a family of acidic ninecarbon sugars that are typically located at the terminal positions of a variety of glycoconjugates. Naturally occurring sialic acids show an immense diversity of structure, and this reflects their involvement in a variety of biologically important processes. One such process involves the direct participation of sialic acids in recognition events through specific interactions with lectins, a family of proteins that recognise and bind sugars. This review will present a detailed overview of our current knowledge regarding the occurrence, specificity and function of sialic acid-specific lectins, particularly those that occur in viruses, bacteria and non-vertebrate eukaryotes. Received 13 December 2005; received after revision 9 February 2006; accepted 15 February 2006     

A common variant associated with prostate cancer in European and African populations

With the increasing incidence of prostate cancer, identifying common genetic variants that confer risk of the disease is important. Here we report such a variant on chromosome 8q24, a region initially identified through a study of Icelandic families. Allele -8 of the microsatellite DG8S737 was associated with prostate cancer in three case-control series of European ancestry from Iceland, Sweden and the US. The estimated odds ratio (OR) of the allele is 1.62 (P = 2.7 x 10(-11)). About 19% of affected men and 13% of the general population carry at least one copy, yielding a population attributable risk (PAR) of approximately 8%. The association was also replicated in an African American case-control group with a similar OR, in which 41% of affected individuals and 30% of the population are carriers. This leads to a greater estimated PAR (16%) that may contribute to higher incidence of prostate cancer in African American men than in men of European ancestry.     

Parallel adaptive origins of digestive RNases in Asian and African leaf monkeys

Similar morphological or physiological changes occurring in multiple evolutionary lineages are not uncommon. Such parallel changes are believed to be adaptive, because a complex character is unlikely to originate more than once by chance. However, the occurrence of adaptive parallel amino acid substitutions is debated. Here I propose four requirements for establishing adaptive parallel evolution at the protein sequence level and use these criteria to demonstrate such a case. I report that the gene encoding pancreatic ribonuclease was duplicated independently in Asian and African leaf-eating monkeys. Statistical analyses of DNA sequences, functional assays of reconstructed ancestral proteins and site-directed mutagenesis show that the new genes acquired enhanced digestive efficiencies through parallel amino acid replacements driven by darwinian selection. They also lost a non-digestive function independently, under a relaxed selective constraint. These results demonstrate that despite the overall stochasticity, even molecular evolution has a certain degree of repeatability and predictability under the pressures of natural selection.     

CXorf6 is a causative gene for hypospadias

46,XY disorders of sex development (DSD) refer to a wide range of abnormal genitalia, including hypospadias, which affects approximately 0.5% of male newborns. We identified three different nonsense mutations of CXorf6 in individuals with hypospadias and found that its mouse homolog was specifically expressed in fetal Sertoli and Leydig cells around the critical period for sex development. These data imply that CXorf6 is a causative gene for hypospadias.     

Common variation in three genes, including a noncoding variant in CFH, strongly influences risk of age-related macular degeneration

Age-related macular degeneration (AMD) is a common, late-onset disease with seemingly typical complexity: recurrence ratios for siblings of an affected individual are three- to sixfold higher than in the general population, and family-based analysis has resulted in only modestly significant evidence for linkage. In a case-control study drawn from a US-based population of European descent, we have identified a previously unrecognized common, noncoding variant in CFH, the gene encoding complement factor H, that substantially increases the influence of this locus on AMD, and we have strongly replicated the associations of four other previously reported common alleles in three genes (P values ranging from 10(-6) to 10(-70)). Despite excellent power to detect epistasis, we observed purely additive accumulation of risk from alleles at these genes. We found no differences in association of these loci with major phenotypic categories of advanced AMD. Genotypes at these five common SNPs define a broad spectrum of interindividual disease risk and explain about half of the classical sibling risk of AMD in our study population.     

Conserved requirement for a plant host cell protein in powdery mildew pathogenesis

In the fungal phylum Ascomycota, the ability to cause disease in plants and animals has been gained and lost repeatedly during phylogenesis. In monocotyledonous barley, loss-of-function mlo alleles result in effective immunity against the Ascomycete Blumeria graminis f. sp. hordei, the causal agent of powdery mildew disease. However, mlo-based disease resistance has been considered a barley-specific phenomenon to date. Here, we demonstrate a conserved requirement for MLO proteins in powdery mildew pathogenesis in the dicotyledonous plant species Arabidopsis thaliana. Epistasis analysis showed that mlo resistance in A. thaliana does not involve the signaling molecules ethylene, jasmonic acid or salicylic acid, but requires a syntaxin, glycosyl hydrolase and ABC transporter. These findings imply that a common host cell entry mechanism of powdery mildew fungi evolved once and at least 200 million years ago, suggesting that within the Erysiphales (powdery mildews) the ability to cause disease has been a stable trait throughout phylogenesis.