Depression,heterosis and carry-over effects after many generations of inbreeding withDrosophila melanogaster

Abeele and Gabarros₄, two inbred lines originating from natural populations, and among which the size was stable at least up to generation 12 and generation 22 respectively, while the viability was decreasing, have been studied in generation 63 and 73 respectively. Different environments including temperature and egg-density conditions were used. The viability and size were diminished to a different extent in the two lines. Hybrids obtained by crossing the 87th and 82nd generation, respectively, of these two lines show a definite heterosis for size and a viability percentage smaller than the one of the parental inbred lines. No reciprocal differences, except in high density conditions, were observed. A second generation, obtained from the F₁ reciprocals raised in different density environments show a breakdown of heterosis for size and a large increase in viability. Carry-over effects due to the different environments in which the reciprocal hybrids were grown were also observed in the second generation. The interference of cytoplasm for transmission of acquired characters seems almost certain. Questions are raised concerning the selection opportunity in inbred lines, the influence of parental inbreeding on the character of the hybrids, the opportuneness of the generalization of the homeostasis idea, and the transmission of acquired characters.     

Patterning of dopaminergic neurotransmitter identity among Caenorhabditis elegans ray sensory neurons by a TGFbeta family signaling pathway and a Hox gene

We have investigated the mechanism that patterns dopamine expression among Caenorhabditis elegans male ray sensory neurons. Dopamine is expressed by the A-type sensory neurons in three out of the nine pairs of rays. We used expression of a tyrosine hydroxylase reporter transgene as well as direct assays for dopamine to study the genetic requirements for adoption of the dopaminergic cell fate. In loss-of-function mutants affecting a TGFbeta family signaling pathway, the DBL-1 pathway, dopaminergic identity is adopted irregularly by a wider subset of the rays. Ectopic expression of the pathway ligand, DBL-1, from a heat-shock-driven transgene results in adoption of dopaminergic identity by rays 3-9; rays 1 and 2 are refractory. The rays are therefore prepatterned with respect to their competence to be induced by a DBL-1 pathway signal. Temperature-shift experiments with a temperature-sensitive type II receptor mutant, as well as heat-shock induction experiments, show that the DBL-1 pathway acts during an interval that extends from two to one cell generation before ray neurons are born and begin to differentiate. In a mutant of the AbdominalB class Hox gene egl-5, rays that normally express EGL-5 do not adopt dopaminergic fate and cannot be induced to express DA when DBL-1 is provided by a heat-shock-driven dbl-1 transgene. Therefore, egl-5 is required for making a subset of rays capable of adopting dopaminergic identity, while the function of the DBL-1 pathway signal is to pattern the realization of this capability.     

Cyclic AMP calcium and the growth of mastocytoma cells

Arresting P815 mastocytoma cell growth with N6, O2'-dibutyryladenosine 3':5' cyclic monophosphate (db cAMP) and theophylline increased 45Ca2+ uptake and efflux by the cells (i.e, Ca2+ cycling) without altering cytoplasmic free Ca2+ concentrations or the amount or distribution of protein kinase C in the cells. Attempts to identify the Ca2+ channels involved using a wide variety of drugs were unsuccessful. However, the inhibitory effect of db cAMP on growth was greatly increase in medium containing low Ca2+ concentrations, confirming that interactions between Ca2+ and cyclic AMP can affect mastocytoma cell growth.