Molecular cloning, gene organization, and expression of mouse Mpi encoding phosphomannose isomerase.
Phosphomannose isomerase (PMI) interconverts fructose-6-P (Fru-6-P) and mannose-6-P (Man-6-P), linking energy metabolism to protein glycosylation. We have cloned the mouse Mpi cDNA, analyzed its genomic organization, and studied the expression in different tissues. The Mpi gene has eight exons covering 7.2 kb. The structure and intron-exon boundaries are essentially the same as its human ortholog with 85% amino acid identity. Mpi is alternatively spliced at the 3' end, resulting in three messages with different 3'-untranslated regions. Mpi expression is regulated at both the transcription and translation levels, with the highest expression level in testis. Rabbit antibodies prepared against mouse PMI expressed in E. coli recognize a single 47-kDa band. Immunohistochemistry of mouse tissues shows general cytosolic staining in all cells. In testis, staining is intense in round spermatids and residual bodies, moderate in pachytene spermatocytes, and weak in spermatogonia and spermatozoa. In contrast, northern blot analysis shows comparable transcripts of 1.8 and 1.6 kb in pachytene spermatocytes and round spermatids, suggesting delayed translation of PMI. The stage-specific expression of PMI in testis may be important for KDN synthesis, which requires Man-6-P, or it may be needed to ensure sufficient glycosylation precursors in cells that do not utilize glucose and instead rely on lactate and pyruvate.
Glycobiology Program, The Burnham Institute, 10901 North Torrey Pines Rd., La Jolla, CA 92037, USA.
Joseph A
JA
Davis
Xiao-Hua
XH
Wu
Ling
L
Wang
Charles
C
DeRossi
Vibeke
V
Westphal
Rongrong
R
Wu
Gordon
G
Alton
Geetha
G
Srikrishna
Hudson H
HH
Freeze
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D018076:DNA, Complementary; D005091:Exons; D007150:Immunohistochemistry; D007438:Introns; D008297:Male; D008359:Mannose-6-Phosphate Isomerase / Q000235:genetics*; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D013094:Spermatozoa / Q000201:enzymology
D018076:DNA, Complementary; D008359:Mannose-6-Phosphate Isomerase