The internal cranial anatomy of the Middle Pleistocene Broken Hill 1 cranium

The cranium (Broken Hill 1 or BH1) from the site previously known as Broken Hill, Northern Rhodesia (now Kabwe, Zambia) is one of the best preserved hominin fossils from the mid-Pleistocene. Its distinctive combination of anatomical features, however, makes its taxonomic attribution ambiguous. High resolution microCT, which has not previously been employed for gross morphological studies of this important specimen, allows a precise description of the internal anatomical features of BH1, including the distribution of cranial vault thickness and its 2 internal composition, paranasal pneumatisation, pneumatisation of the temporal bone and endocranial anatomy. Relative to other chronologically and taxonomically relevant specimens, BH1 shows unusually marked paranasal pneumatisation and a fairly thick cranial vault. For many of the features analysed, this fossil does not exhibit the apomorphic conditions observed in either Neandertals or Homo sapiens. Its morphology and the general shape of the brain and of the skull may be partly explained by an allometric relationship relative to the features observed in Homo erectus s.l. However, further research is still necessary to better appreciate the cranial anatomy of BH1 and the role of Homo rhodesiensis/Homo heidelbergensis in the course of human evolution. This paper also deals with more general aspects of scientific practices in palaeoanthropology. In particular, we give precise descriptions of many internal anatomical features of Broken Hill 1, a specimen discovered in 1921. This important and unique dataset will allow independent comparative studies in the future. However, we were limited in our study by the very restricted amount of comparative information available for Homo fossils. In our view, scientific papers dealing with the anatomical description of hominin specimens, both in the case of announcements of new discoveries and of discussions of important specimens found decades ago, should always include qualitative and quantitative data that truly allow for further independent research.CBS and LTB thank the Calleva Foundation and the Human Origins Research Fund for funding

Mutations in the Polycomb Group Gene polyhomeotic Lead to Epithelial Instability in both the Ovary and Wing Imaginal Disc in Drosophila

Most human cancers originate from epithelial tissues and cell polarity and adhesion defects can lead to metastasis. The Polycomb-Group of chromatin factors were first characterized in Drosophila as repressors of homeotic genes during development, while studies in mammals indicate a conserved role in body plan organization, as well as an implication in other processes such as stem cell maintenance, cell proliferation, and tumorigenesis. We have analyzed the function of the Drosophila Polycomb-Group gene polyhomeotic in epithelial cells of two different organs, the ovary and the wing imaginal disc.Clonal analysis of loss and gain of function of polyhomeotic resulted in segregation between mutant and wild-type cells in both the follicular and wing imaginal disc epithelia, without excessive cell proliferation. Both basal and apical expulsion of mutant cells was observed, the former characterized by specific reorganization of cell adhesion and polarity proteins, the latter by complete cytoplasmic diffusion of these proteins. Among several candidate target genes tested, only the homeotic gene Abdominal-B was a target of PH in both ovarian and wing disc cells. Although overexpression of Abdominal-B was sufficient to cause cell segregation in the wing disc, epistatic analysis indicated that the presence of Abdominal-B is not necessary for expulsion of polyhomeotic mutant epithelial cells suggesting that additional polyhomeotic targets are implicated in this phenomenon.Our results indicate that polyhomeotic mutations have a direct effect on epithelial integrity that can be uncoupled from overproliferation. We show that cells in an epithelium expressing different levels of polyhomeotic sort out indicating differential adhesive properties between the cell populations. Interestingly, we found distinct modalities between apical and basal expulsion of ph mutant cells and further studies of this phenomenon should allow parallels to be made with the modified adhesive and polarity properties of different types of epithelial tumors

Dynamics and Mechanical Stability of the Developing Dorsoventral Organizer of the Wing Imaginal Disc

Shaping the primordia during development relies on forces and mechanisms able to control cell segregation. In the imaginal discs of Drosophila the cellular populations that will give rise to the dorsal and ventral parts on the wing blade are segregated and do not intermingle. A cellular population that becomes specified by the boundary of the dorsal and ventral cellular domains, the so-called organizer, controls this process. In this paper we study the dynamics and stability of the dorsal-ventral organizer of the wing imaginal disc of Drosophila as cell proliferation advances. Our approach is based on a vertex model to perform in silico experiments that are fully dynamical and take into account the available experimental data such as: cell packing properties, orientation of the cellular divisions, response upon membrane ablation, and robustness to mechanical perturbations induced by fast growing clones. Our results shed light on the complex interplay between the cytoskeleton mechanics, the cell cycle, the cell growth, and the cellular interactions in order to shape the dorsal-ventral organizer as a robust source of positional information and a lineage controller. Specifically, we elucidate the necessary and sufficient ingredients that enforce its functionality: distinctive mechanical properties, including increased tension, longer cell cycle duration, and a cleavage criterion that satisfies the Hertwig rule. Our results provide novel insights into the developmental mechanisms that drive the dynamics of the DV organizer and set a definition of the so-called Notch fence model in quantitative terms

The Ice Age diet of the La Quina 5 Neandertal of southwest France

Horizon 2020(H2020)677576Bioarchaeolog

The Ice Age diet of the La Quina 5 Neandertal of southwest France

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Multifaceted modes of γ-tubulin complex recruitment and microtubule nucleation at mitotic centrosomes

Funder: Centre National de la Recherche ScientifiqueFunder: Fondation Bettencourt SchuellerMicrotubule nucleation is mediated by γ-tubulin ring complexes (γ-TuRCs). In most eukaryotes, a GCP4/5/4/6 “core” complex promotes γ-tubulin small complex (γ-TuSC) association to generate cytosolic γ-TuRCs. Unlike γ-TuSCs, however, this core complex is non-essential in various species and absent from budding yeasts. In Drosophila, Spindle defective-2 (Spd-2) and Centrosomin (Cnn) redundantly recruit γ-tubulin complexes to mitotic centrosomes. Here, we show that Spd-2 recruits γ-TuRCs formed via the GCP4/5/4/6 core, but Cnn can recruit γ-TuSCs directly via its well-conserved CM1 domain, similar to its homologs in budding yeast. When centrosomes fail to recruit γ-tubulin complexes, they still nucleate microtubules via the TOG domain protein Mini-spindles (Msps), but these microtubules have different dynamic properties. Our data, therefore, help explain the dispensability of the GCP4/5/4/6 core and highlight the robustness of centrosomes as microtubule organizing centers. They also suggest that the dynamic properties of microtubules are influenced by how they are nucleated.</jats:p

Multifaceted modes of γ-tubulin complex recruitment and microtubule nucleation at mitotic centrosomes

Microtubule nucleation is mediated by γ-tubulin ring complexes (γ-TuRCs). In most eukaryotes, a GCP4/5/4/6 “core” complex promotes γ-tubulin small complex (γ-TuSC) association to generate cytosolic γ-TuRCs. Unlike γ-TuSCs, however, this core complex is non-essential in various species and absent from budding yeasts. In Drosophila, Spindle defective-2 (Spd-2) and Centrosomin (Cnn) redundantly recruit γ-tubulin complexes to mitotic centrosomes. Here we show that Spd-2 recruits γ-TuRCs formed via the GCP4/5/4/6 core, but that Cnn can recruit γ-TuSCs directly via its well-conserved CM1 domain, similar to its homologues in budding yeast. When centrosomes fail to recruit γ-tubulin complexes, they still nucleate microtubules via the TOG domain protein Mini-spindles (Msps), but these microtubules have different dynamic properties. Our data therefore help explain the dispensability of the GCP4/5/4/6 core and highlight the robustness of centrosomes as microtubule organising centres. They also suggest that the dynamic properties of microtubules are influenced by how they were nucleated