Currently if you wish to pursue an MCSE in Exchange 2013 (or SharePoint or Lync) you required an MSCA in Windows 2012 first. However, Microsoft have now changed this requirement so as an alternative, an MCSA in Office 365 can now be used as the pre-requisite certification. For many professionals in the communication and collaboration field this may be a much more sensible approach.
Details of the Office 365 MCSA can be found at https://www.microsoft.com/learning/en-us/mcsa-office365-certification.aspx