The Ospreys and Blues have pleaded for support after being handed control of rugby in the region formerly held by the now-defunct Celtic Warriors.
The Ospreys are responsible for the Bridgend area, with the Blues given Rhondda Cynon Taff, along with the Vale of Glamorgan and south Powys.
"We must all get behind this and pull in the same direction," said WRU general manager Steve Lewis.
"There is a clear path for youngsters to become professional players."
Lewis added: "Development has long been based on unitary authorities and now we've made the boundaries of the regions co-terminous with those.
"The structure for the development of our game is still there and it is very effective."
Ospreys chief executive Andrew Donald fears that there may well be simmering anger over the closure of the Warriors.
"People are emotional and upset," he said. "Just because we have changed the boundaries does not mean people will automatically change their allegiance so we have no God-given right to expect those supporters to come and watch us.
"What we must do is aim to take that pain away by creating an attractive product that makes them want to be involved."
The Ospreys have confirmed that they are in negotiations to play some games at Bridgend's Brewery Field.
The Blues face perhaps an even more difficult task in winning over Cardiff's traditional rivals from the valleys.
Blues chief executive Robert Norster told BBC Sport Wales: "I'm a realist and I know the entrenched views some hold, that's what makes our nation love the game.
"I know there are a lot of cultural and other barriers to break down to win over clubs we've not had relations with in the past.
"But I sincerely hope people see this for what it is, one of the last chances we've got to make the professional game a success."
Norster suggested that a lack of funding from the Union made the job of the regional sides even more difficult.
"There isn't a pot to dip into to generate the activities we'd like to," he said. "But we'll make every effort to make things work for the entire region."
The Blues will have to decide whether to play outside Cardiff
Lewis said it was down to the regions themselves to decide how to sell themselves away from their home bases and whether they should play matches in the old Warriors region.
"The regions have to satisfy hospitality demands and their sponsors, but they also have to engage disaffected people in the regions so compromises may have to be made," said Lewis.
"The WRU can attempt to influence and sway opinion, but it is not our decision."