Anterior-posterior polarity in Drosophila arises from the movement of the oocyte to the posterior of the egg chamber, and the subsequent acquisition of posterior fate by the adjacent somatic follicle cells. We demonstrate that gurken is necessary in the oocyte and torpedo/DER in the follicle cells for the induction of posterior fate. As the gurken-torpedo/DER pathway also establishes dorsoventral polarity later in oogenesis, Drosophila uses the same germline to soma signalling pathway to determine both embryonic axes.

The mago nashi gene plays two essential roles in Drosophila axis formation: it is required downstream of the signal from the posterior follicle cells for the polarisation of the oocyte microtubule cytoskeleton, and has a second, independent role in the localisation of oskar mRNA to the posterior of the oocyte.

The two main body axes in Drosophila become polarised as a result of a series of symmetry-breaking steps during oogenesis. Two of the sixteen germline cells in each egg chamber develop as pro-oocytes, and the first asymmetry arises when one of these cells is selected to become the oocyte. Anterior-posterior polarity originates when the oocyte then comes to lie posterior to the nurse cells and signals through the Gurken/Egfr pathway to induce the adjacent follicle cells to adopt a posterior fate. This directs the movement of the germinal vesicle and associated gurken mRNA from the posterior to an anterior corner of the oocyte, where Gurken protein signals for a second time to induce the dorsal follicle cells, thereby polarising the dorsal-ventral axis. Here we describe a group of five genes, the spindle loci, which are required for each of these polarising events. spindle mutants inhibit the induction of both the posterior and dorsal follicle cells by disrupting the localisation and translation of gurken mRNA. Moreover, the oocyte often fails to reach the posterior of mutant egg chambers and differentiates abnormally. Finally, double mutants cause both pro-oocytes to develop as oocytes, by delaying the choice between these two cells. Thus, these mutants reveal a novel link between oocyte selection, oocyte positioning and axis formation in Drosophila, leading us to propose that the spindle genes act in a process that is common to several of these events.

No abstract

Growth in amphibians presents a variety of problems which may be investigated by the method of transplantation. Studies by this means have proved fruitful in the analysis, for example, of the following questions: The stability of specific growth rate, tested by the heteroplastic transplantation of organs;2 the influence on size of functional:' and mechanical4 factors ; growth correlations between structures closely related in their development ;3 and the regulation of disharmonic I n view of the fact that a compreliensive review of the transplantation experiments dealing wit11 growth in amphibians is now in preparation, we shall in the present paper postpone, in so far as possible, further refer-'Sections Ia and I1 of this paper are the product of a collaborative investigatioil by both authors during thc spring aid summer of 1933 a t Stanford liniversity. The remaiiiiiig sections, with exceptions to be noted in the text, a r e a description of experiments performed by the senior author at Yale University during the years 1929-1931.We wish to seknowledge our obligation to Profs. 3 ' . W. Weymouth airtl W. H.Rich, of Stanford University, for their suggestions coiiceriiing the statistical treatment of p a r t of our data.