Isolation and characterization of Xenopus laevis aldolase B cDNA and expression patterns of aldolase A, B and C genes in adult tissues, oocytes and embryos of Xenopus laevis

Following previous cloning and expression studies of Xenopus aldolase C (br ain-type) and A (muscle-type) cDNAs, we cloned here two Xenopus aldolase B (liver-type) cDNAs (XALDB1 and XALDB2, 2447 and 1490 bp, respectively) usin g two different liver libraries. These cDNAs had very similar ORF with only one conservative amino acid substitution, but 3'-UTR of XALDB1 contained c a. 1 kb of unrelated reiterated sequence probably ligated during library co nstruction as shown by genomic Southern blot analysis. In adult, aldolase B mRNA (ca. 1.8 kb) was expressed strongly in kidney, liver, stomach, intest ine, moderately strongly in skin, and very weakly in all the other tissues including muscles and brain, which strongly express aldolase A and C mRNAs, respectively. In oocytes and early embryos, aldolase A and C mRNAs occurre d abundantly as maternal mRNAs, but aldolase B mRNA occurred only at a resi dual level, and its strong expression started only after the late neurula s tage, mainly in liver rudiment, pronephros, epidermis and proctodeum. Thus, active expression of the gene for aldolase B, involved in dietary fructose metabolism, starts only later during development (but before the feeding s tage), albeit genes for aldolases A and C, involved in glycolysis, are expr essed abundantly from early stages of embryogenesis, during which embryos d evelop depending on yolk as the only energy source. (C) 2000 Elsevier Scien ce B,V. All rights reserved.