In the cis-Golgi, Man7, Man8 or Man9 N-glycans are progressively trimmed to Man5 N-glycans. The reaction can be catalyzed by one of three known mannosidases, expressed in different tissues and with slightly different affinity. These enzymes trim the mannoses in a different order (Tremblay and Herscovics, 2000), but produce the same output with 5 mannoses.
A small confusion on the nomenclature of these genes coding for these enzymes is present in the literature: the standard HGNC symbols are MAN1A1, MAN1A2, MAN1C1, but MAN1A2 is also referred to as MAN1B in certain publications, while MAN1B1 is the enzyme acting in the ERQC compartment on unfolded glycoproteins. Moreover, the names do not correspond to a preference of these enzymes for which of the three mannose branches these trim first.