Disruption of homeobox containing gene, hbx9 results in the deregulation of prestalk cell patterning in Dictyostelium discoideum.

We have earlier classified the homeobox containing genes from Dictyostelium discoideum and identified 5 genes belonging to the TALE class. Here, we have characterized hbx9, a member of TALE class. In situ hybridization results show it to be preferentially expressed in the prestalkA (pstA) cells but not in the prestalkO (pstO) cells. Disruption of the hbx9 gene in Ax2 cells delay initiation of development and also slows cell proliferation. There was decreased cadA expression during the development of hbx9 cells, which results in inappropriate cell contacts, altered cell motility and patterning properties. ecmA and ecmB were mis-expressed in the pstO and pstA regions resulting in an effectively smaller pstO region. Surprisingly, the total ecmAO expression in pstAO cells was comparable to the wild type, suggesting that in hbx9 cells, ecmA was expressed in the pstO region. In hbx9, proportioning and patterning was altered in favour of pstA cell-type. Moreover, precocious expression of ecmB and pspA was also observed in the vegetative cells. Expression profiling of components of cAMP signalling suggest that Hbx9 controls cell proportioning of prestalk cells by modulating cAMP signalling during growth-to-development transition.