Hmgcr promotes a long-range signal to attract Drosophila germ cells independently of Hedgehog

During development many cell types migrate along stereotyped routes determined through deployment of cell surface or secreted guidance molecules. Whilst we know the identity of many of these molecules, the distances over which they natively operate can be difficult to determine. Here we have quantified the range of an attractive signal for the migration of Drosophila germ cells. Their migration is guided by an attractive signal generated by the expression of genes in the 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase (Hmgcr) pathway, and by a repulsive signal generated by the expression of Wunens. We demonstrate that the attractive signal downstream of Hmgcr is cell-contact independent and acts at long range, the extent of which depends on Hmgcr levels. This range would be sufficient to reach all of the germ cells for their entire migration. Furthermore, Hmgcr-mediated attraction does not require Wunens but can operate simultaneously with Wunen-mediated repulsion. Lastly, several papers posit Hedgehog (Hh) as being the germ cell attractant downstream of hmgcr. Here we provide evidence that this is not the case.