Abnormalities in the cell-division cycle in Roberts syndrome fibroblasts: a cellular basis for the phenotypic characteristics?

Roberts-SC phocomelia syndrome (RS) is a recessively inherited developmental disorder characterized by profound pre- and postnatal growth reduction, symmetrical limb reductions of varying severity, and craniofacial abnormalities. Many patients with RS exhibit a striking chromosomal abnormality involving the heterochromatic, C-banding regions of most chromosomes. Dermal fibroblast strains from three such patients were used to investigate in vitro cellular growth characteristics. Plating efficiency, colony-forming ability, and cell density at confluence in RS were compared with dermal fibroblast strains from pediatric patients without RS and fetal lung fibroblast strains. Time-lapse cinematography was used to study mitotic duration and cytokinesis in RS and various control fibroblast strains. Clearly, cell from affected individuals had deficiencies that led to a multitude of abnormalities at the cellular level. These included: abnormal mitosis and cytokinesis, reduced cell growth, atypical cell morphology, and altered chromosomal morphology at peri- and paracentromeric and nucleolar-organizing regions. These findings suggest that the basis for at least some of the phenotypic abnormalities characteristic of this trait may reside in the reduced growth rates of the cells during the course of development. This could account for the reduced pre- and postnatal growth rates as well as for the developmental abnormalities, since deficiencies of cells in developing anlagen could well lead to alterations in developmental patterns.     

Status‐dependence and morphological trade‐offs in the expression of a sexually selected character in the mite,Sancassania berlesei

Abstract In the male dimorphic mite Sancassania berlesei, fighter males kill rivals with a pair of armoured legs whereas scrambler males are benign with unmodified legs. In an adaptive response mediated by colony pheromones, fighter expression increases at low colony density. Under the status‐dependent evolutionarily stable strategy (ESS) model we expected heavier final instar nymphs to become fighters. This was supported in group reared nymphs. In individually reared nymphs fighter expression was experimentally suppressed using two concentrations of colony pheromone. Here, male morph expression again depended on tritonymphal body mass and contact is therefore unnecessary for individuals to judge their status. Fighter suppression was greater in the higher pheromone treatment, but morph determination remained status dependent. The weight and length of fighters was lower than scramblers of same‐weight final instar nymphs, indicating a developmental trade‐off, and a cost not recouped at the adult stage.