Join certain Lines in a large text file

Hello 

I am looking for simple POWERSHELL  script to join  lines based on some criteria at the end 

Original file 

MYLINE11-

MyLine12-

MyLine13

* comment char

MyLine21-

MyLine22-

MyLine23

Need Output as below in output file 

MYLINE11MYLINE12MYLINE13

MYLINE21MYLINE22MYLINE23

Any help appreciated