Table 2.
Summary of knock-out (KO), knock-in (KI) or transgenic (Tg) mice for assessing gene function of alkaline phosphatase (ALP) family.
| Methods | Target Gene |
Outcome (Note) | Reference |
|---|---|---|---|
| Overexpression | ALPP | Tg mice overexpressing human PLALP systemically were produced. There were no adverse effects on mouse development or viability. | [20,21] |
| Gene targeting for KO | ALP1 | Homozygous mutants (called Akp3−/−) were histologically normal and fertile. However, accelerated transport of fat droplets through the intestinal epithelium and elevation of serum triglyceride levels were discernible, which was associated with higher intestinal Ca2+ uptake. | [22,23] |
| Overexpression | ALPP2 | Tg mouse lines harboring human ALPP2 linked to short or long promoter region of ALPP2 were produced. A 450 bp promoter sequence directs GCALP expression to the intestine and endothelial cells, while a 1.7 kb promoter sequence directs GCALP expression to the spermatogenic lineage and to the eight-cell embryos through the blastocysts. | [24] |
| Gene targeting for KO | Akp5 (Alpl2) | No obvious phenotypic abnormalities. Normal reproductive activity with acquisition of live offspring, indicating the nonessential role of EAP during embryonic development. | [25] |
| Gene targeting for KO | Akp5 (Alpl2) | In homozygous mutants (called EAP.ko), preimplantation embryos exhibited slower development and higher rates of degeneration, delayed parturition, and reduced litter size. | [26] |
| Gene targeting for KI | ALPL | In homozygous mutants (called Alpltm1Sor), primordial germ cells appear unaffected indicating that ALPL is not essential for their development or migration. At first, the mice exhibited normal skeletal development; however, homozygous mutant mice developed seizures and apnea at approximately two weeks after birth, and died before weaning. Rescued animals subsequently develop defective dentition. TNSALP modulates T lymphocyte function (specifically T cell-dependent colitis) when examined using heterozygous Alpltm1Sor mice. | [27,28,29] |
| Gene targeting for KO | ALPL | In homozygous mutants (called Alpltm1Jlm or Akp2−/−), abnormal bone mineralization was evident. Morphological changes in the osteoblasts, aberrant development of the lumbar nerve roots, disturbances in intestinal physiology, increased apoptosis in the thymus, and abnormal spleens are also discernible. Loss of ALPL causes myelin abnormalities and synaptic dysfunction. | [25,30,31] |
| Gene targeting for KI | ALPL | KI of Cre expression unit was carried out into the region between exons 6 and 7 of ALPL gene. The resulting line was called Alpltm1(cre)Nagy. After crossed Alpltm1(cre)Nagy line with the double-reporter line, Z/AP, human ALP expression is discernible in PGCs at E9.5–10.5. After mid-gestation, however, it was also expressed in the labyrinthine region of the placenta, the intestine and the neural tube. | [32] |
| Gene targeting for KI | ALPL | KI of an around 12 kb genomic sequence of Akp2 in which two loxP sites (located in introns 2 and 4, respectively) and a cassette containing neomycin resistance gene expression unit into the endogenous Akp2 locus. This floxed mouse (called Alplflox/flox) is normal in the absence of Cre expression. However, in the presence of Cre, the deletion of exons 3 and 4 should occur, which may result in the ablation of endogenous TNSALP expression. | [33] |
| Overexpression | ALPL | Tg mouse line (called “Col1a1-Tnap”) expressing human ALPL under control of an osteoblast-specific collagen type I α1 chain (Col1a1) promoter was produced. This line is healthy and exhibits increased bone mineralization. | [34] |
| Overexpression | ALPL | Tg mice carrying human ALPL under the vascular smooth muscle cell-specific transgelin (Tagln) promoter were produced. They developed severe arterial medial calcification and reduced viability. | [35] |
| Overexpression | ALPL | Tg mice (celled “Endothelial TNSALP mice”) carrying ALPL under the endothelial-specific tunica intima endothelial kinase 2 (Tie2) promoter were produced. They survived well into adulthood and displayed generalized arterial calcification together with elevated blood pressure and compensatory left ventricular hypertrophy. | [36] |
Abbreviations: ALPL, tissue-nonspecific ALP (TNSALP); E, embryonic day; EAP, embryonic ALP; GCALP, germ cell ALP; PGC, primordial germ cell; PLALP, placental ALP.