Mechanisms of Adhesion Among Cells of the Early Chick Blastoderm

Cells from the extraembryonic endoderm of the gastrulating chick embryo contain a β-d-galactoside-binding lectin inhibited by thiodigalactoside (TDG). TDG inhibits the aggregation of freshly prepared cells. In these fresh cell suspensions, adhesion is also inhibited when purified lectin is added to the aggregation assay. If these cells are incubated at 22° C their adhesion decreases. Associated with this is an increase in lectin activity in the cell supernatants. In these incubated cells aggregation is stimulated by TDG and desialyzed fetuin. These data suggest that the lectin may have a role to play in cellular adhesion. Under some experimental conditions extraembryonic endoderm cells from rosettes with trypsinized glutaraldehyde-fixed rabbit erythrocytes. This phenomenon is inhibited, to a certain extent, by TDG.     

Experimental Approach to the Role of Protozoa in Aquatic Ecosystems

In enrichment batch experiments, samples from three water bodieswere alternatively supplemented by various amounts of organicmaterial and incubated at 20 C. Colpidium campylum reached itshighest total cell volumes in cultures with the highest initialtotal cell volumes in cultures with the highest initial concentrationsof organics; Cyclidium glaucoma preferred lower concentrations;and Glaucoma chattoni occupied the intermediate position. Noneof the species preferred any special type of organic material.In two-stage continuous-flow units, a mixed culture of bacteriawas kept in stage I and the clones of ciliates were maintainedin stage II. The interrelations between the total cell volumesof ciliates at various concentrations of bactopeptone were inaccordance with the results from the enrichment experiments.Since the growth of bacteria continued in the presence of ciliates,a four-stage apparatus was constructed in which a bacterialculture was raised and diluted in three stages before enteringthe culture ofColpidium. The bacterial growth in the presenceof Colpidium was not eliminated even by this arrangement, asdemonstrated by dosing antibiotics along with bacteria. An effectof ciliate metabolites on bacterial growth rate is suggested,completing a metabolic cycle in the bacteria-protozoa system.     

Asymmetric size and shape variation in the Central European transect across the house mouse hybrid zone

We studied asymmetric variation of the mandible in the Central European portion of the hybrid zone between two house mouse subspecies, Mus musculus musculus and Mus musculus domesticus. Within introgression classes, defined by the share of diagnostic allozymes, we quantified the directional and fluctuating component of asymmetric variation, as well as skewness and kurtosis of individual asymmetry distributions. Furthermore, in the same manner we re‐analysed asymmetric variation of the ventral side of the skull. According to the quadratic polynomial model, the mandible shape‐fluctuating asymmetry, but not size‐fluctuating asymmetry, was significantly decreased in the centre of the hybrid zone (with a minimum predicted for a hybrid index of 0.41). On the contrary, the skull shape‐fluctuating asymmetry non‐monotonically increased towards the musculus side of the hybrid zone (with a peak predicted for a hybrid index of 0.86). Thus, the impact of hybridization on fluctuating asymmetry is trait‐specific in this portion of the house mouse hybrid zone. The only general feature of asymmetric variation we observed was the shift towards the platykurtosis of asymmetry distributions in the centre of the hybrid zone. Taken together, we suggest genetic variability for right–left asymmetries to be generally increased, but the developmental instability of mandible shape to be decreased, by hybridization. We hypothesize the decrease of developmental instability to be caused by overdominant effects on developmental dynamics rather than by increased heterozygosity. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 13–27.     

Confrontation of Developing Melanophore Bars of Dark and White Axolotls With Endogenous Dark-Embryo Mannose-Binding Lectin Correlates With Melanophore Bar Disruption

Lectins are carbohydrate-binding proteins suggested to be important in embryonic cell adhesion/differentiation. Dark and white axolotls contain an endogenous mannosebinding lectin that is especially prevalent during larval melanophore pattern formation (Martha et al., 1990). To determine if this lectin can alter melanophore patterning, lectin extracts have been isolated from Dark embryos by affinity chromatography. The main protein band is 44K on SDS-PAGE. Dark and white embryos at the early chromatophore migration stage have been confronted with Dark lectin or its nonmetabolized inhibitor, 2-deoxyglucose (2-DG). The barred melanophore pattern of both genotypes is disrupted by lectin or 2-DG treatment suggesting that endogenous mannose-binding lectin and its receptor participate in bar formation.