Response : Estimating the Age of the Common Ancestor of Men from the ZFY Intron

Effects of Emdogain on osteoblast gene expression

OBJECTIVE

Emdogain (EMD) is a protein extract purified from porcine enamel and has been introduced in clinical practice to obtain periodontal regeneration. EMD is composed mainly of amelogenins (90%), while the remaining 10% is composed of non-amelogenin enamel matrix proteins such as enamelins, tuftelin, amelin and ameloblastin. Enamel matrix proteins seem to be involved in root formation. EMD has been reported to promote proliferation, migration, adhesion and differentiation of cells associated with healing periodontal tissues in vivo.

DESIGN

How this protein acts on osteoblasts is poorly understood. We therefore attempted to address this question by using a microarray technique to identify genes that are differently regulated in osteoblasts exposed to enamel matrix proteins.

RESULTS

By using DNA microarrays containing 20,000 genes, we identified several upregulated and downregulated genes in the osteoblast-like cell line (MG-63) cultured with enamel matrix proteins (Emd). The differentially expressed genes cover a broad range of functional activities: (i) signaling transduction, (ii) transcription, (iii) translation, (iv) cell cycle regulation, proliferation and apoptosis, (v) immune system, (vi) vesicular transport and lysosome activity, and (vii) cytoskeleton, cell adhesion and extracellular matrix production.

CONCLUSIONS

The data reported are the first genome-wide scan of the effect of enamel matrix proteins on osteoblast-like cells. These results can contribute to our understanding of the molecular mechanisms of bone regeneration and as a model for comparing other materials with similar clinical effects.

Population bottlenecks and Pleistocene human evolution

We review the anatomical and archaeological evidence for an early population bottleneck in humans and bracket the time when it could have occurred. We outline the subsequent demographic changes that the archaeological evidence of range expansions and contractions address, and we examine how inbreeding effective population size provides an alternative view of past population size change. This addresses the question of other, more recent, population size bottlenecks, and we review nonrecombining and recombining genetic systems that may reflect them. We examine how these genetic data constrain the possibility of significant population size bottlenecks (i.e., of sufficiently small size and/or long duration to minimize genetic variation in autosomal and haploid systems) at several different critical times in human history. Different constraints appear in nonrecombining and recombining systems, and among the autosomal loci most are incompatible with any Pleistocene population size expansions. Microsatellite data seem to show Pleistocene population size expansions, but in aggregate they are difficult to interpret because different microsatellite studies do not show the same expansion. The archaeological data are only compatible with a few of these analyses, most prominently with data from Alu elements, and we use these facts to question whether the view of the past from analysis of inbreeding effective population size is valid. Finally, we examine the issue of whether inbreeding effective population size provides any reasonable measure of the actual past size of the human species. We contend that if the evidence of a population size bottleneck early in the evolution of our lineage is accepted, most genetic data either lack the resolution to address subsequent changes in the human population or do not meet the assumptions required to do so validly. It is our conclusion that, at the moment, genetic data cannot disprove a simple model of exponential population growth following a bottleneck 2 MYA at the origin of our lineage and extending through the Pleistocene. Archaeological and paleontological data indicate that this model is too oversimplified to be an accurate reflection of detailed population history, and therefore we find that genetic data lack the resolution to validly reflect many details of Pleistocene human population change. However, there is one detail that these data are sufficient to address. Both genetic and anthropological data are incompatible with the hypothesis of a recent population size bottleneck. Such an event would be expected to leave a significant mark across numerous genetic loci and observable anatomical traits, but while some subsets of data are compatible with a recent population size bottleneck, there is no consistently expressed effect that can be found across the range where it should appear, and this absence disproves the hypothesis.