Transcription factor, which binds preferentially the consensus sequence 5'-TAAGT[AG]-3' and can behave as a transcriptional repressor (By similarity). Plays an important role in normal prostate development, regulating proliferation of glandular epithelium and in the formation of ducts in prostate (PubMed:10215624). Acts as a tumor suppressor controlling prostate carcinogenesis, as shown by the ability to suppress growth and tumorigenicity of prostate carcinoma cells (PubMed:12036903). Plays a role in the formation of minor salivary glands (particularly palatine and lingual glands) (PubMed:10906459). Interacts with serum response factor (SRF) (PubMed:16814806). Interacts with SPDEF. Interacts with WDR77. Interacts with TOPORS which polyubiquitinates NKX3-1 and induces its proteasomal degradation (By similarity). Interacts with FEM1B (PubMed:18816836). Expressed mostly in the male urogenital tract, with highest expression in the epithelial cells lining the ducts of anterior, dorsolateral and ventral prostate and in the bulbourethral gland, and much lower in the seminal vesicle and the testis (PubMed:8943214, PubMed:9142502, PubMed:10215624). Expression in the prostate increases during sexual maturation and is drastically reduced following castration. Expressed also in brain (hippocampus and external granular layer of the cerebral cortex), kidney (intralobular arteries), thymus and adrenal and salivary glands (PubMed:8943214, PubMed:9142502). Early marker of the sclerotome and of a subset of vascular smooth muscle cells, expressed also in outgrowths of epithelial cells, in ectodermal epithelial cells and in restricted regions of the central nervous system. Detected first at 7.5 dpc in the paraxial mesoderm adjacent to the neural fold. At 8.5 dpc, segmental expression in the first 8 or 9 somites. Expression proceeds caudally in parallel with somite maturation and is restricted to the sclerotome. As the somites mature, expression moves away from the axial structures, becomes transiently restricted to a subset of early myotomal cells at the dorsal medial lip and is subsequently down-regulated. At 10.5 dpc, expressed only in the most caudal immature somites. At 9.5 dpc, present in the dorsal aorta. At 11.5 dpc, restricted to the vascular smooth muscle cells of caudal region of the dorsal aorta. At 12.5 dpc, expressed in the distal epithelium of the tongue and in Rathke pouch (anterior pituitary). By 13.5 dpc, also detected in tooth buds. Expression in the abdominal aorta continues through 11.5 to 15.5 dpc. Detected in the vertebral vessels at 12.5 dpc, in the carotid vessel at 13.5 dpc and in arcuate and interlobular arteries of the kidney at 15.5 dpc. In neonates, present in palatine glands, epithelial root sheath of the tooth and epithelial hair sheath. In the nervous system of neonates, expressed in the olfactory lobe, olfactory epithelial cells and cerebellar cortex. Expressed in the male urogenital system during late embryogenesis: at day 14.5, expressed in the outbuddings of the pelvic region of the urogenital sinus, and, at lower levels, in the prospective urethra. Expression is confined to the epithelial cells that are invaginating into the surrounding mesenchyme, with highest levels at the leading edge. At 17.5 dpc, present in the developing ventral, dorsolateral and anterior prostatic buds, in the nascent bulbourethral glands, as well as in the epithelial ducts that join the glands to the prospective urethra. During postnatal growth and morphogenesis of the prostate, high expression is maintain at sites of ductal outgrowth and branching. In the developing testis, detected at 14.5 and 17.5 dpc in the medullary cords, which form seminiferous tubules. By androgens (PubMed:8943214). During embryonic development, induced and maintained by sonic hedgehog in pre-somitic mesoderm, in immature somites and in urogenital sinus, but not in the other expression domains (PubMed:10906459). Ubiquitinated by TOPORS; monoubiquitinated at several residues and also polyubiquitinated on single residues. Defects in prostate ductal morphogenesis and secretory protein production (PubMed:10215624, PubMed:10906459). The bulbourethral gland displays prostatic epithelial hyperplasia, which increases in severity with age (PubMed:10215624, PubMed:10906459). Mice also display morphogenetic defects of minor salivary glands, which are reduced in size and exhibit severely altered duct morphology (PubMed:10906459). Belongs to the NK-3 homeobox family.