Hormone receptor 3: Biological Overview | Evolutionary Homologs | Regulation | Developmental Biology | Effects of Mutation | References

Gene name - Hormone receptor 3

Synonyms -Hormone receptor-like in 46

Cytological map position - 46F1--46F11

Function - Transcription factor

Keywords - molting, imaginal discs, gut, salivary gland, epidermis

Symbol - Hr3

FlyBase ID: FBgn0000448

Genetic map position - 2-[59]

Classification - nuclear receptor superfamily ROR homolog

Cellular location - nuclear

NCBI link: Entrez Gene
Hr3 orthologs: Biolitmine
Recent literature
Wang, X., Wang, H., Liu, L., Li, S., Emery, G. and Chen, J. (2020). Temporal Coordination of Collective Migration and Lumen Formation by Antagonism between Two Nuclear Receptors. iScience 23(7): 101335. PubMed ID: 32682323
During development, cells undergo multiple, distinct morphogenetic processes to form a tissue or organ, but how their temporal order and time interval are determined remain poorly understood. This study shows that the nuclear receptors E75 and DHR3 regulate the temporal order and time interval between the collective migration and lumen formation of a coherent group of cells named border cells during Drosophila oogenesis. E75, in response to ecdysone signaling, antagonizes the activity of DHR3 during border cell migration, and DHR3 is necessary and sufficient for the subsequent lumen formation that is critical for micropyle morphogenesis. DHR3's lumen-inducing function is mainly mediated through βFtz-f1, another nuclear receptor and transcription factor. Furthermore, both DHR3 and βFtz-f1 are required for chitin secretion into the lumen, whereas DHR3 is sufficient for chitin secretion. Lastly, DHR3 and βFtz-f1 suppress JNK signaling in the border cells to downregulate cell adhesion during lumen formation.
Lama, C., Love, C. R., Le, H. N., Waqar, M., Reeve, J. L., Lama, J. and Dauwalder, B. (2022). The nuclear receptor Hr46/Hr3 is required in the blood brain barrier of mature males for courtship. PLoS Genet 18(1): e1009519. PubMed ID: 35077443
The blood brain barrier (BBB) forms a stringent barrier that protects the brain from components in the circulation that could interfere with neuronal function. At the same time, the BBB enables selective transport of critical nutrients and other chemicals to the brain. Beyond these functions, another recently recognized function is even less characterized, specifically the role of the BBB in modulating behavior by affecting neuronal function in a sex-dependent manner. Notably, signaling in the adult Drosophila BBB is required for normal male courtship behavior. Courtship regulation also relies on male-specific molecules in the BBB. Previous studies have demonstrated that adult feminization of these cells in males significantly lowered courtship. In this study microarray analysis was carried out of BBB cells isolated from males and females. Findings revealed that these cells contain male- and female-enriched transcripts, respectively. Among these transcripts, nuclear receptor Hr46/Hr3 was identified as a male-enriched BBB transcript. Hr46/Hr3 is best known for its essential roles in the ecdysone response during development and metamorphosis. This study demonstrated that Hr46/Hr3 is specifically required in the BBB cells for courtship behavior in mature males. The protein is localized in the nuclei of sub-perineurial glial cells (SPG), indicating that it might act as a transcriptional regulator. These data provide a catalogue of sexually dimorphic BBB transcripts and demonstrate a physiological adult role for the nuclear receptor Hr46/Hr3 in the regulation of male courtship, a novel function that is independent of its developmental role.
Bunker, J., Bashir, M., Bailey, S., Boodram, P., Perry, A., Delaney, R., Tsachaki, M., Sprecher, S. G., Nelson, E., Call, G. B. and Rister, J. (2023). Blimp-1/PRDM1 and Hr3/RORβ specify the blue-sensitive photoreceptor subtype in Drosophila by repressing the hippo pathway. Front Cell Dev Biol 11: 1058961. PubMed ID: 36960411
During terminal differentiation of the mammalian retina, transcription factors control binary cell fate decisions that generate functionally distinct subtypes of photoreceptor neurons. For instance, Otx2 and RORβ activate the expression of the transcriptional repressor Blimp-1/PRDM1 that represses bipolar interneuron fate and promotes rod photoreceptor fate. Moreover, Otx2 and Crx promote expression of the nuclear receptor Nrl that promotes rod photoreceptor fate and represses cone photoreceptor fate. Mutations in these four transcription factors cause severe eye diseases such as retinitis pigmentosa. This study shows that a post-mitotic binary fate decision in Drosophila color photoreceptor subtype specification requires ecdysone signaling and involves orthologs of these transcription factors: Drosophila Blimp-1/PRDM1 and Hr3/RORβ promote blue-sensitive (Rh5) photoreceptor fate and repress green-sensitive (Rh6) photoreceptor fate through the transcriptional repression of warts/LATS, the nexus of the phylogenetically conserved Hippo tumor suppressor pathway. Moreover, a novel interaction was identified between Blimp-1 and warts, whereby Blimp-1 represses a warts intronic enhancer in blue-sensitive photoreceptors and thereby gives rise to specific expression of warts in green-sensitive photoreceptors. Together, these results reveal that conserved transcriptional regulators play key roles in terminal cell fate decisions in both the Drosophila and the mammalian retina, and the mechanistic insights further deepen understanding of how Hippo pathway signaling is repurposed to control photoreceptor fates for Drosophila color vision.

The Drosophila gene Hormone receptor-like in 46 (Hr46), previously known as DHR3, is an orphan nuclear receptor. The designation "orphan" refers to the fact that unlike other nuclear receptors whose ligands are known, the ligand activating Hr46 is not known, nor is it even certain that a ligand for this protein even exists. Hr46 is homologous to the mammalian orphan nuclear receptor RORalpha (Giguere, 1995).

Before delving into the biology of Hr46 function, a few words about Drosophila nuclear receptors are in order. One might ask, why should biologists interested in human development study Drosophila molting hormones? After all, humans do not molt, leaving Drosophila molting hormones an audience limited to those investigating amphibian or reptilian molting, for example. Studies in these areas might look to the Drosophila molting heirarchy as a model system, but why would anyone else bother? This narrow viewpoint is fallacious as well, when examined in terms of current understanding of the roles played by nuclear hormones in mammalian development.

Perhaps the most well documented involvement of nuclear hormone receptors in mammalian development has to do with the regulation of Hox cluster genes. Hoxa-1 and Hoxa-2 are homologs of Drosophila genes labial and proboscipedia, respectively. In both mouse and Drosophila, these genes have been shown to play a critical role in head development. One enhancer regulating Hoxa-1 and Hoxa-2 expression contains a retinoic acid response element. Point mutations within the retinoic acid response element abolish expression in neuroepithelium caudal to rhombomere 4, supporting a natural role for retinoid responsive nuclear receptors in patterning of the hindbrain and spinal cord. Analysis of the murine Hoxa-2 rhombomere 2-specific enhancer in Drosophila embryos reveals a distinct expression domain within the fly head segments, which parallels the expression domain of proboscipedia. These results suggest an evolutionary conservation between HOM-C/Hox family members, including a conservation of certain DNA regulatory elements and possible regulatory cascades involving nuclear hormone receptors (Frasch, 1995).

Thus it is clear that aspects of a molting hierarchy, at least as far as nuclear hormone receptors, are conserved in mammals. What is this pathway and how does it function in development? The answer to this question is unexpected, and not by any means complete. In Drosophila, the source of molting hormone is the prothoracic gland. In humans, although the genes regulate growth as though there were a central source of the hormone retinoic acid, such a source might not function in hindbrain and spinal cord segmentation. Retinaldehyde dehydrogenase type 2, a major retinoic acid generating enzyme in the early embryo is expressed in mesoderm in the entire posterior part of the embryo up to the base of the headfolds, while there is no more rostral (towards the head) expression (Niederreither, 1997). Perhaps, Hox genes are regulated by nuclear hormone receptors based on intracellular signals modulated as if there were a central source of hormone. The nuclear receptors follow a similar dynamic to that found in flies and frogs, but the response may be cell autonomous and not regulated by exogenously supplied hormone. It could be that the pathway has been evolutionarily conserved, but that the external regulation has been lost. A definitive confirmation of this conclusion awaits more detailed examination of the distribution of retinoids in mammals.

The retinoid responsive nuclear receptors in mammals involved in Hox cluster regulation are only distantly related to Drosophila Ecdysone receptor. EcR is most closely related to the vertebrate Farnesoid X receptor (Mangelsdorf, 1995). Ultraspiracle, a closer homolog of mammalian retinoic acid RXR receptor, functions in Drosophila as a dimerization partner with Ecdysone receptor, the central regulator of the molting process. Perhaps a better analogy than the one given above involving molting would be the mammalian response to thyroid hormone. In this case the response is to an exogenous hormone (thyroxin). The transcription factor components are similar; thyroxin receptor (TR) plays a homologous role to the Ecdysone receptor, and RXR, the partner of TR, plays a homologous role to Ultraspiracle (Collingwood, 1997).

Hr46 represents a second tier regulator, one that acts negatively on Ecdysone receptor. Thus Hr46 plays a direct role in regulating the nuclear receptor hormones involved in Drosophila molting and whose cell autonomous regulation in mammals remains somewhat a mystery. Hr46 acts negatively on Ecdysone receptor and postively on genes expressed subsequently in the molting hierarchy. Perhaps by understanding the gene and protein interactions in Drosophila molting, clues can be discovered as to the roles of nuclear receptors in mammalian development (White, 1997).

Hr46 is termed a early-late gene. This means that it is expressed after early genes such as Ecdysone receptor and before the late hormones involved in metamorphosis. In the early stages of Drosophila metamorphosis, during the formation of pupa (the process of pupariation), prior to metamorphosis into the adult, Hr46 represses the ecdysone induction of early genes turned on by the pulse of ecdysone that triggers pupariation. Hr46 is shown to interact directly with the Ecdysone receptor. The mechanism of Hr46 repression may involve an interaction between the Hr46 and Ecdysone receptor ligand binding domains. Thus the repressive function of Hr46 does not involve binding to DNA but instead involves physical interaction with the Ecdysone receptor (White, 1997).

Hr46 also induces ßFTZF1, an orphan nuclear receptor that is essential for the appropriate response to the subsequent prepupal pulse of ecdysone. This induction requires binding of Hr46 to DNA. The DNA binding domain of Hr46 is necessary for the activating function of Hr46. Another nuclear receptor, the E75B receptor, classified as an early gene, regulates Hr46. E75B lacks a complete DNA binding domain, and inhibits the inductive function of Hr46 by forming a complex with Hr46 on the ßFTZF1 promoter, thereby providing a timing mechanism for ßFTZF1 induction that is dependent on the disappearance of E75B. Hr46 appears to bind the ßFTZF1 promoter as a monomer, since sequencing and footprinting analysis have uncovered single consensus Hr46 sites at each of these DNA sites. E75B fails to bind DNA in the absence of Hr46. Thus E75B acts like a co-repressor with Hr46, rather than as a competitor with Hr46 for DNA binding. The restricted temporal expression of E75B apparently acts as a precise timer for the onset of ßFTZF1 expression (White, 1997).

Hr46 targets a number of proteins besides EcR and ßFTZF1. Hr46 is sufficient to repress BR-C, E74A, E75A and E78B transcription. BR-C, E74A, E75A and E78B are considered early genes that are induced by ecdysone. In the repressive function Hr46 is likely to act through the Ecdysone receptor. In addition, however, direct interaction with the promoters of these genes is likely, as Hr46 is found associated with their salivary gland puffs (Lam, 1997). Hr46 thus appears to function as a switch that defines the larval-prepupal transition by arresting the early regulatory response to ecdysone at puparium formation and facilitating the induction of the betaFTZ-F1 competence factor in mid-prepupae (Lam, 1997).


At least three Hr46 transcripts of approximately 5.5, 7, and 9 kb are detected, of which the 9-kb transcript is observed only during pupal development (Koelle, 1992).

Genomic length - 18 kb

Bases in 5' UTR - 227

Exons - 9

Bases in 3' UTR - 2.5 kb


Amino Acids - 487

Structural Domains

Hr46 contains two conserved domains characteristic of steroid receptor superfamily members. The more N-terminal and the more C-terminal of these conserved domains are referred to as the C and E regions respectively. The C regions is a 67 amino acid sequence that has been shown to function as a Zn finger DNA binding domain. The E region is an 225 amino acid domain that functions as a hormone binding domain in vertebrate receptors. Knirps, Knirps-related and Egon proteins show homology to the C but not the E region (Koelle, 1992).

ROR alpha isoforms bind to response elements consisting of a single copy of the core recognition sequence AGGTCA preceded by a 6-bp A/T-rich sequence; the distinct amino-terminal domains of each isoform influence DNA-binding specificity. ROR alpha 1 presumably binds along one face of the DNA helix as a monomer. By analogy to previous studies of the orphan receptors NGFI-B and FTZ-F1, extensive mutational analysis of the ROR alpha 1 protein shows that a domain extending from the carboxy-terminal end of the second conserved zinc-binding motif is required for specific DNA recognition. However, point mutations and domain swap experiments between ROR alpha 1 and NGFI-B demonstrate that sequence-specific recognition dictated by the carboxy-terminal extension is determined by distinct subdomains in the two receptors. These results demonstrate that monomeric nuclear receptors utilize diverse mechanisms to achieve high-affinity and specific DNA binding and that ROR alpha 1 represents the prototype for a distinct subfamily of monomeric orphan nuclear receptors (Giguere, 1995).

ROR alpha 1 and ROR alpha 2 bind as monomers to a DNA recognition sequence composed of two distinct moieties, a 3' nuclear receptor core half-site AGGTCA preceded by a 5' AT-rich sequence. Recognition of this bipartite hormone response element (RORE) requires both the zinc-binding motifs and a group of amino acid residues located at the carboxy-terminal end of the DNA-binding domain (DBD) which is referred to here as the carboxy-terminal extension. Binding of ROR alpha 1 and ROR alpha 2 to the RORE induces a large DNA bend of approximately 130 degrees that may be important for receptor function. The overall direction of the DNA bend is towards the major groove at the center of the 3' AGGTCA half-site. The presence of the nonconserved hinge region, located between the DBD and the putative ligand-binding domain (LBD) of ROR alpha, is required for maximal DNA bending. Deletion of a large portion of the amino-terminal domain (NTD) of the ROR alpha protein does not alter the DNA bend angle but shifts the DNA bend center 5' relative to the bend induced by intact ROR alpha. Methylation interference studies using the NTD-deleted ROR alpha 1 mutant indicate that some DNA contacts in the 5' AT-rich half of the RORE are also shifted 5', while those in the 3' AGGTCA half-site are unaffected. These results are consistent with a model in which the ROR alpha NTD and the nonconserved hinge region orient the zinc-binding motifs and the carboxy-terminal extension of the ROR alpha DBD relative to each other in order to achieve proper interactions with the two halves of its recognition site. Transactivation studies suggest that both protein-induced DNA bending and protein-protein interactions are important for receptor function (McBroom, 1995).

Hormone receptor-like in 46: Evolutionary Homologs | Regulation | Developmental Biology | Effects of Mutation | References

date revised: 22 March 2022  

Home page: The Interactive Fly © 1995, 1996 Thomas B. Brody, Ph.D.

The Interactive Fly resides on the
Society for Developmental Biology's Web server.