Probes for CRE

Abstract

BACKGROUND:

The origin of the intercalated cushions that develop into the anterior cusp of the pulmonary valve (PV) and the noncoronary cusp of the aortic valve (AV) is not well understood.

RESULTS:

Cre transgenes in combination with the Rosa TdTomato-EGFP reporter were used to generate three-dimensional lineage mapping of AV and PV cusps during intercalated cushion development. Tie2-Cre;EGFP was used to mark endothelial-derived mesenchymal cells, Wnt1-Cre;EGFP for cardiac neural crest and cardiac Troponin T (Tnnt2)Cre;EGFP, for myocardial lineage. The highest percentage of intercalated cushion cells at embryonic day (E) 12.5 was Tnnt2-Cre; EGFP positive; 68.0% for the PV and 50.0% AV. Neither Tnnt2 mRNA nor Tnnt2-Cre protein was expressed in the intercalated cushions; and the Tnnt2-Cre lineage intercalated cushion cells were also positive for the mesenchymal markers Sox9 and versican. Tnnt2-Cre lineage was present within the forming intercalated cushions from E11.5 and was present in the intercalated cushion derived PV and AV cusps and localized to the fibrosa layer at postnatal day 0.

CONCLUSIONS:

Intercalated cushions of the developing outflow tract are populated with Tnnt2-Cre derived cells, a Cre reporter previously used for tracing and excision of myocardial cells and not previously associated with mesenchymal cells.

The collecting duct is the predominant nephron site of prorenin and prorenin receptor (PRR) expression. We previously demonstrated that the collecting duct PRR regulates epithelial Na+ channel (ENaC) activity and water transport; however, which cell type is involved remains unclear. Herein, we examined the effects of principal cell (PC) or intercalated cell (IC) PRR deletion on renal Na+ and water handling. PC or IC PRR KO mice were obtained by crossing floxed PRR mice with mice harboring Cre recombinase under the control of the AQP2 or B-1 subunit of the H+ ATPase promoters, respectively. PC KO mice had reduced renal medullary ENaC-α abundance and increased urinary Na+ losses on a low Na+ diet compared to controls. Conversely, IC KO mice had no apparent differences in Na+ balance or ENaC abundance compared to controls. Acute treatment with prorenin increased ENaC channel number and open probability in acutely isolated cortical collecting ducts from control and IC PRR KO, but not PC PRR KO, mice. Further, compared to controls, PC KO, but not IC KO mice, had increased urine volume, reduced urine osmolality, and reduced abundance of renal medullary AQP2. Taken together, these findings indicate that PC, but not IC, PRR modulates ENaC activity, urinary Na+ excretion and water transport.