Vunipola replaces Marler
Mako Vunipola will start at loosehead prop for England in Saturday's RBS 6 Nations match against Italy, due to the unavailability of Joe Marler.
The Saracens player steps in because Marler will miss the climax to the 2014 RBS 6 Nations campaign as his partner is expecting their first child.
The Rugby Football Union confirmed on Thursday night that Vunipola will be promoted to the starting XV, with 23-year-old Marler staying in London to be present at the birth rather than accompany the squad to Rome.
With Alex Corbisiero recovering from a knee injury, England have elevated fourth-choice loosehead Matt Mullan to the bench.
Head coach Stuart Lancaster said: "It is important that Joe is with his partner at this exciting time.
"Family must always come first and everyone in the squad wishes them well. We have prepared for being without Joe and we have no doubt Mako will slot straight in and perform, as will Matt Mullan should he get an opportunity.
"Matt played in the autumn internationals. There's no problem with him, he's been involved right throughout the campaign. He's a good player to come on."
England are locked in a three-way battle for the Six Nations title alongside Ireland and France, although it is the Irish who occupy the driving seat due to their vastly superior points difference.
Victory in Rome in the opening match of the day is the minimum requirement, with an avalanche of tries to overhaul the 49-point deficit on Brian O'Driscoll's men the perfect scenario.
Recent history points to a hard-fought encounter decided by one score, however, with England prevailing 19-15 in Rome two years ago and 18-11 in the return fixture at Twickenham last season.
Two such narrow wins have made Lancaster cautious over targeting anything other than victory.
"Winning is the priority. We went there two years ago and there were different conditions. It was very difficult," he said.
"Look at the Scotland game, that was 21-20. Italy beat France last year and Ireland also lost. Wales and Australia both struggled two years ago.
"It's not an easy place to go and get a lot of points. We know what's coming."
England's Six Nations opened with an undeserved late defeat at the Stade de France, but they have since been propelled back into title contention with impressive victories over Scotland, Ireland and Wales.
Lancaster is determined that the resilience and skill that has enabled the Red Rose to rescue their hopes of claiming their first major piece of silverware since 2011 will be maintained until end.
"When we get out there I'm sure mentally we'll be excited about the game," he said.
"It's a fantastic opportunity to finish the Six Nations on a high.
"We want to make sure we put in a performance that backs up the previous performances we've put in so far. That's a big motivation for the players.
"It's always harder in the Six Nations when you have two games at home and three away.
"The character we've shown has been excellent throughout. The attitude and desire to improve has been exceptional.
"But we have to back that up with a final performance that means we leave the Six Nations in a positive state of mind for the New Zealand tour."