Answer:
The principal difference in development of Dorsoventral axis in deuterostomes and protostomes is something called inversion
Explanation:
In protostomates the neural tube is below the gut and the dorsal vessel is above the gut while in deuterostomates is the oppossite, there is an inversion and now, the neural tube is above the gut and the heart tube is below. In both cases the development is related to the gradient of expression of some genes, where the expresion of one gene supress the formation of one structure in one side of the axis.
In protostomates the TGT-B factor is expressed dorsally and supress neural tube formation and ventrally a sog gene is expressed and supress TGT-F factor allowing neural tube to develop. In deuterostomates, an homolog of TGT-B family gene BMP-4 is expressed ventrally while dorsally BMP inhibitors (sog gene like) are expressed.
Accordingly to some researchers, the first state of the common ancestor of deuterostomates and protostomates had an protostomate-like orientation in dorsoventral axis
