TESTIS-SPECIFIC EXPRESSION OF MESSENGER-RNAS FOR A UNIQUE HUMAN TYPE-1 HEXOKINASE LACKING THE PORIN-BINDING DOMAIN

Several enzymes in the glycolytic pathway are reported to have spermat ogenic cell-specific isozymes. We reported recently the cloning of cDN As representing three unique type 1 hexokinase mRNAs (mHk1-sa, mHk1-sb , and mHk1-sc) present only in mouse spermatogenic cells and the patte rns of expression of these mRNAs (Mori et al., 1993: Biol Reprod 49:19 1-203). The mRNAs contain a spermatogenic cell-specific sequence, but lack the sequence for the porin-binding domain that somatic cell hexok inases use to bind to a pore-forming protein in the outer mitochondria l membrane. We now report the cloning of cDNAs representing three uniq ue human type 1 hexokinase mRNAs (hHK1-ta, hHK1-tb, and hHK1-tc) expre ssed in testis, but not detected by Northern analysis in other human t issues. These mRNAs also contain a testis-specific sequence not presen t in somatic cell type 1 hexokinase, but lack the sequence for the por in-binding domain. The hHK1-tb and hHK1-tc mRNAs each contain an addit ional unique sequence. The testis-specific sequence of the human mRNAs is similar to the spermatogenic cell-specific sequence of the mouse m RNAs. Furthermore, Northern analysis of RNA from mouse, hamster, guine a pig, rabbit, ram, human, and rat demonstrated expression of type 1 h exokinase mRNAs lacking the porin-binding domain in the testes of thes e mammals. These results suggest that hexokinase may have unique struc tural or functional features in spermatogenic cells and support a mode l proposed by others for hexokinase gene evolution in mammals. (C) 199 6 Wiley-Liss, Inc.