The planarian HOM HOX homeobox genes (Plox) expressed along the anteroposterior axis

In the freshwater planarian Dugesia japonica, five cDNAs for HOM/HOX homeob ox genes were cloned and sequenced. Together with sequence data on MOM/HOX homeobox genes of platyhelminthes deposited in databases, comparison of the deduced amino acid sequences revealed that planarians have at least seven HOM/HOX homeobox genes, Plox1 to Plox7 (planarian HOM/HOX homeobox genes). Whole-mount in situ hybridization and RT-PCR revealed that Plox4 and Plox5 were increasingly expressed along a spatial gradient in the posterior regio n of intact animals. During regeneration, Plox5 was expressed only in the p osterior region of regenerating body pieces, suggesting that the gene is in volved ill the anteroposterior patterning in planarians. Plox5 was not foun d to be expressed in a blastema-specific manner, which contradicts a previo us report (J. R. Bayascas, E. Castillo, A. M. Munos-Marmol, and E. Salo. De velopment 124, 141-148, 1997). X-ray irradiation experiments showed that Pl ox5 was expressed at least in some cells other than neoblasts, but that the induction of Plox5 expression during regeneration might require neoblasts. (C) 1999 Academic Press.