Population structuring in species inhabiting marine environments such as the Northeast Atlantic Ocean (NEA) and Mediterranean Sea (MS) has usually been explained based on past and present physical barriers to gene flow and isolation by distance (IBD). Here, we examined the relative importance of these factors on population structuring of the common cuttlefish Sepia officinalis by using methods of phylogenetic inference and hypothesis testing coupled with coalescent and classical population genetic parameter estimation. Individuals from 10 Atlantic and 15 Mediterranean sites were sequenced for 659 bp of the mitochondrial COI gene (259 sequences). IBD seems to be the main factor driving present and past genetic structuring of Sepia populations across the NEA-MS, both at large and small geographical scales. Such an evolutionary process agrees well with some of the biological features characterizing this cuttlefish species (short migrations, nektobenthic habit, benthic eggs hatching directly to benthic juveniles). Despite the many barriers to migration/gene flow suggested in the NEA-MS region, genetic population fragmentation due to past isolation of water masses (Pleistocene; 0.56 million years ago) and/or present-day oceanographic currents was only detected between the Aegean-Ionian and western Mediterranean Seas. Restricted gene flow associated with the Almería-Oran hydrographic front was also suggested between southern and eastern Spanish populations. Distinct population boundaries could not be clearly determined, except for the Aegean-Ionian stock. Two Atlantic and five Mediterranean samples showed evidence of current decline in genetic diversity, which may indicate over-exploitation of Sepia in both marine regions.

The Transforming growth factor β (Tgf-β) pathway, by signaling via the activation of Smad transcription factors, induces the expression of many diverse downstream target genes thereby regulating a vast array of cellular events essential for proper development and homeostasis. In order for a specific cell type to properly interpret the Tgf-β signal and elicit a specific cellular response, cell-specific transcriptional co-factors often cooperate with the Smads to activate a discrete set of genes in the appropriate temporal and spatial manner. Here, via a conditional knockout approach, we show that mice mutant for Forkhead Box O transcription factor FoxO1 exhibit an enamel hypomaturation defect which phenocopies that of the Smad3 mutant mice. Furthermore, we determined that both the FoxO1 and Smad3 mutant teeth exhibit changes in the expression of similar cohort of genes encoding enamel matrix proteins required for proper enamel development. These data raise the possibility that FoxO1 and Smad3 act in concert to regulate a common repertoire of genes necessary for complete enamel maturation. This study is the first to define an essential role for the FoxO family of transcription factors in tooth development and provides a new molecular entry point which will allow researchers to delineate novel genetic pathways regulating the process of biomineralization which may also have significance for studies of human tooth diseases such as amelogenesis imperfecta.

Transcriptional enhancers are genomic sequences bound by transcription factors that act together with basal transcriptional machinery to regulate gene transcription. Several high-throughput methods have generated large datasets of tissue-specific enhancer sequences with putative roles in developmental processes. However, few enhancers have been deleted from the genome to determine their roles in development. To understand the roles of two enhancers active in the mouse embryonic limb bud we deleted them from the genome. Although the genes regulated by these enhancers are unknown, they were selected because they were identified in a screen for putative limb bud-specific enhancers associated with p300, an acetyltransferase that participates in protein complexes that promote active transcription, and because the orthologous human enhancers (H1442 and H280) drive distinct lacZ expression patterns in limb buds of embryonic day (E) 11.5 transgenic mice. We show that the orthologous mouse sequences, M280 and M1442, regulate dynamic expression in the developing limb. Although significant transcriptional differences in enhancer-proximal genes in embryonic limb buds accompany the deletion of M280 and M1442 no gross limb malformations during embryonic development were observed, demonstrating that M280 and M1442 are not required for mouse limb development. However, M280 is required for the development and/or maintenance of body size; M280 mice are significantly smaller than controls. M280 also harbors an “ultraconserved” sequence that is identical between human, rat, and mouse. This is the first report of a phenotype resulting from the deletion of an ultraconserved element. These studies highlight the importance of determining enhancer regulatory function by experiments that manipulate them in situ and suggest that some of an enhancer's regulatory capacities may be developmentally tolerated rather than developmentally required.

The helmeted appearance of the black mastiff bat, Molossus rufus, at embryonic stage 21 results from the anterior margins of the ears being progressively situated near the facial midline during development. Comparative bat embryology provides a foundation for understanding unique mammalian and chiropteran (bat) adaptations, such as the marked ability of M. rufus to use its compactly folded wings during terrestrial quadrupedal locomotion. See Nolte et al., on page 155, in this issue.