Low nephron endowment is strongly associated with cardiovascular disease, especially hypertension. Sine oculis homeobox 2 (Six2) is the master transcriptional regulator in balancing self-renewal and differentiation of nephron progenitor cells (NPCs) for appropriate nephron endowment. Loss of
Six2
in mice causes early-onset loss of self-renewal and premature differentiation of NPCs. However, it is unclear how Six2 is functionally regulated during nephrogenesis.
In vivo
interaction of histone deacetylase1 and 2 (Hdac1/2) to Six2 was detected in developing kidney by co-immunoprecipitation and proximity ligation assay. Chromatin immunoprecipitation and DNA sequencing experiments in isolated E16.5 NPCs revealed 1,180 (84.58%) of the Six2 peaks overlapped with Hdac2 peaks, implying the involvement of Hdac1/2 in Six2 DNA binding and its function in NPCs. To test whether Hdac1/2 are required for Six2 function to regulate nephron formation, we employed Six2
GC
mouse line, in which the eGFP and Cre fusion gene (GC) replaces and fully recapitulates the endogenous Six2 gene expression pattern. Analysis of kidneys at embryonic day (E) 19.5 and newborn (P0) showed that Six2 heterozygous (Six2
GC
) together with three alleles knockout of
Hdac1/2
resulted in severely hypoplastic kidneys, while three alleles knockout of
Hdac1/2
by transgenic Six2-Cre only led to very subtle phenotypes. Immunostaining at E 19.5 and P0 revealed about 50% reduction of Six2 level in the kidney of Six2
GC
only and Six2
GC
together with three alleles knockout of
Hdac1/2
mice. In the kidneys of Six2 heterozygous mice, no change was observed for most of the NPC identity makers for self-renewal, including the three Six2 targets, Pax2, Sall1 and WT1. However, sequential removal of three alleles of
Hdac1/2
of Six2
GC
mice did not change Six2 protein level but significantly decreased the expression of Pax2, Sall1 and WT1, suggesting the requirement of Hdac1/2 for Six2’s function to transcriptionally activate the expression of its target genes. We also observed the premature differentiation and decreased nephron formation in mutant kidneys. Therefore, we conclude that Hdac1/2 are required for Six2’s function to promote NPC self-renewal and repress premature differentiation during nephrogenesis.
Concurrent BMP7 and FGF9 signalling governs AP-1 function to promote self-renewal of nephron progenitor cells
