Mice null for the Ren‐1d gene lack renin storage granules in their juxtaglomerular cells and exhibit altered macula densa morphology. Three lines of transgenic mice carrying a 55kbp transgene encompassing the human renin (hRen) locus were generated and crossed onto a Ren1d‐null background. Expression of hRen was seen to restore granulation in juxtaglomerular (JG) cells in a transgene expression level‐dependent manner, suggesting that a threshold level of renin expression is required for the formation of dense renin‐containing granules. Complementation of the phenotype by the human enzyme suggests that hRen and mouse Ren1d share conserved epitopes required for trafficking renin into the regulated secretion pathway and hence for granulopoiesis. To dissect the granulation phenotype in detail, 2D electron microscopic (EM) images were taken of kidney sections, which were then reconstructed in 3D to show the full extent of renin granular structure. As expected, the expression of hRen, which does not effectively cleave mouse angiotensinogen, was unable to restore macula densa morphology, indicating that a locally active RAS is required for normal macular densa structure and function.

A series of experiments have been carried out to determine whether follicles secrete factors able to affect the growth and development of other, like-sized follicles. Late preantral mouse ovarian follicles were either cocultured or cultured in media conditioned by previously cultured follicles. In particular, the experiments examined whether follicles do secrete such factors, whether the level of FSH in the culture media can affect that process, and what the nature of such secretory factor(s) might be. First, pairs of follicles were cocultured across a polycarbonate membrane containing pores. This showed that communication between the follicles resulted in the stimulation of growth and that the stimulation was due, at least in part, to the production of secretory factor(s). In subsequent experiments, follicles were cultured in media that had been preconditioned by previously cultured follicles. The concentration of FSH in the cultures determined the effect of the conditioned media: conditioned media was stimulatory to follicle growth when levels of FSH remained high throughout the culture, but inhibitory when FSH levels were dropped midway through the cultures. Heat inactivation removed this inhibitory effect, showing that the factor was likely to be a protein; addition of follistatin to the conditioned media did not alter its effect, indicating that the factor was unlikely to be activin. We have shown through a series of culture experiments that mouse follicles secrete factor(s) that can affect the development of other like-sized follicles when cultured from the late preantral to Graafian stages. Furthermore, we have shown that the effect (or production) of such factors is dependent on the FSH environment of the follicles.