Biology:NOBOX

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Short description: Protein-coding gene in the species Homo sapiens


A representation of the 3D structure of the protein myoglobin showing turquoise α-helices.
Generic protein structure example

Homeobox protein NOBOX, also known as newborn ovary homeobox protein, is a protein that in humans is encoded by the NOBOX gene.[1][2][3] The official symbol (NOBOX) and the official full name (NOBOX oogenesis homeobox) are maintained by the HGNC. The NOBOX gene is conserved in chimpanzee, Rhesus monkey, cow, mouse, and rat. There are 175 organisms that have orthologs with human gene NOBOX. It is capable of regulating other genes that are important in the development of follicles. Follicles do not develop and oocytes decrease in its absence which lead to infertility.[4]

Discovery

NOBOX is an in silico subtraction discovery when Suzumori et al. searched for novel genes involved in early mammalian folliculogenesis in 2002. It is one of the several genes that appeared in the search in expressed sequence tag (EST) databases of mouse.[2] It was then cloned and characterised for its genomic structure.

Gene location

The human NOBOX is located in chromosome 7q35 while the mouse NOBOX is in proximal chromosome 6.

Protein structure

The human NOBOX is a 14 kb protein and encoded by 8 exons.[2] It has a proline rich C terminus and contains putative SH3 and WW domains.[5] This C terminus is believed to be critical in its transcriptional activities when bound to oocyte-specific genes.[6] NOBOX belongs to the family of proteins that contains homeodomain. Homeodomain is a stretch of 32 specific amino acids in primates downstream the NOBOX Arg303 residue and is very well-conserved among the species.[7] It contains an asparagine residue at position 51 which is important for its interactions with DNA base pairs.[8][9][10]

Function

NOBOX is a homeobox gene that is preferentially expressed in oocytes. In mice, it is essential for folliculogenesis and regulation of oocyte-specific genes.[3] Regulation of these oocyte-specific genes is thru direct binding of NOBOX to its promoter regions via the specific consensus sequences, the NOBOX DNA binding elements (NBEs). There are three NBEs that have been identified: 5'-TAATTG-3', 5'-TAGTTG-3', and 5'-TAATTA-3'.[6] Knockout study of NOBOX against wild-type ovaries in newborn female mice revealed that 74% (28/38 genes) were downregulated more than 5-fold and 15% (5/33 genes) were upregulated more than 5-fold.[11] However, microRNA population is not affected by NOBOX in newborn ovaries. NOBOX also plays an important role in the suppression of male-determining genes such as Dmrt1.[11] Its deficiency can cause rapid loss of postnatal oocytes and during its absence in female mice, follicles are replaced by fibrous tissue.[2] Recently, a new role of NOBOX in controlling the G2/M arrest was discovered.[12]

Mutations and clinical significance

A mutation in the NOBOX gene is associated with premature ovarian failure (POF), also known as premature ovarian insufficiency (POI).[13] It is a condition which ovaries loss its normal function before the age of 40. It is a heritable disease in up to 30% of patients which is characterised by secondary infertility, amenorrhea, hypoestrogenism, and elevated follicle-stimulating hormone levels in the serum (FSH>40IU/liter).[14][15] It affects ≈1% of women below 40 years old.[16] A study conducted on 96 white women with POF revealed one case of heterozygous mutation in the NOBOX homeodomain, p.Arg355His, in one patient.[13] This mutation was absent in the control population and significantly disrupts the binding of NOBOX to the NBE. Arg355 is critical to DNA binding and is conserved in the homeodomain of the NOBOX from zebrafish to humans. Moreover, its significant negative effect suggests that NOBOX homeodomain may function as a dimer but its rare occurrence suggests a low contribution to POF. Further investigations on POF were conducted on Caucasian, African, Chinese, and Japanese women diagnosed with POF. Several NOBOX loss-of-function mutations were observed in Caucasian and African women accounting to 6.2%, 5.6% and 6.4%.[7][17][18] These results suggest that NOBOX gene is a strong autosomal candidate for POF and its genetic mechanism involves haploinsufficiency. However, these mutations were not found in Chinese and Japanese women making it a less common explanation for POF in the region.[19][20]

The POF syndrome is a highly heterogenous clinical disorder but a recent study showed the first homozygous mutation associated with NOBOX loss-of-function.[12] One patient out of 96 population diagnosed with POF in China was found with one novel homozygous truncating variant in the NOBOX gene. This truncated variant caused a defective transcriptional activation of GDF9, a well-known target of NOBOX, which led to the lost ability of NOBOX to induce G2/M arrest. This finding disagrees that mutation is a less common explanation for POF in Asian population.

Understanding the mutations in NOBOX homeodomain is important to researchers and clinicians to develop diagnostic and therapeutic approaches for POF such as genetic control of mammalian reproductive life-span, regulation of fertility, and generation of mature eggs in the lab.[4]

Interactions

  1. GDF9[6][21]
  2. POU5F1[2][6][4]
  3. DNMT10[4]
  4. FOXL2[22]
  5. FIGLA[4]
  6. RSPO2[23]
  7. DMRT1[15]

References

  1. ↑ "Entrez Gene: NOBOX oogenesis homeobox". https://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=135935. 
  2. ↑ 2.0 2.1 2.2 2.3 2.4 "Nobox is a homeobox-encoding gene preferentially expressed in primordial and growing oocytes". Mechanisms of Development 111 (1–2): 137–41. February 2002. doi:10.1016/S0925-4773(01)00620-7. PMID 11804785. 
  3. ↑ 3.0 3.1 "cDNA cloning and expression of the human NOBOX gene in oocytes and ovarian follicles". Molecular Human Reproduction 12 (5): 283–9. May 2006. doi:10.1093/molehr/gal035. PMID 16597639. 
  4. ↑ 4.0 4.1 4.2 4.3 4.4 "NOBOX deficiency disrupts early folliculogenesis and oocyte-specific gene expression". Science 305 (5687): 1157–9. August 2004. doi:10.1126/science.1099755. PMID 15326356. Bibcode: 2004Sci...305.1157R. 
  5. ↑ "The importance of being proline: the interaction of proline-rich motifs in signaling proteins with their cognate domains". FASEB Journal 14 (2): 231–41. February 2000. doi:10.1096/fasebj.14.2.231. PMID 10657980. 
  6. ↑ 6.0 6.1 6.2 6.3 "Characterization of NOBOX DNA binding specificity and its regulation of Gdf9 and Pou5f1 promoters". The Journal of Biological Chemistry 281 (47): 35747–56. November 2006. doi:10.1074/jbc.M604008200. PMID 16997917. 
  7. ↑ 7.0 7.1 "Novel NOBOX loss-of-function mutations account for 6.2% of cases in a large primary ovarian insufficiency cohort". Human Mutation 32 (10): 1108–13. October 2011. doi:10.1002/humu.21543. PMID 21837770. 
  8. ↑ "DNA binding specificity of homeodomains" (in EN). Biochemistry 30 (48): 11357–67. December 1991. doi:10.1021/bi00112a001. PMID 1742275. 
  9. ↑ "Comparison of X-ray and NMR structures for the Antennapedia homeodomain-DNA complex". Nature Structural Biology 5 (8): 692–7. August 1998. doi:10.1038/1382. PMID 9699632. 
  10. ↑ "Crystal structure of an engrailed homeodomain-DNA complex at 2.8 A resolution: a framework for understanding homeodomain-DNA interactions". Cell 63 (3): 579–90. November 1990. doi:10.1016/0092-8674(90)90453-l. PMID 1977522. 
  11. ↑ 11.0 11.1 "Microarray analyses of newborn mouse ovaries lacking Nobox". Biology of Reproduction 77 (2): 312–9. August 2007. doi:10.1095/biolreprod.107.060459. PMID 17494914. 
  12. ↑ 12.0 12.1 "A homozygous NOBOX truncating variant causes defective transcriptional activation and leads to primary ovarian insufficiency". Human Reproduction 32 (1): 248–255. January 2017. doi:10.1093/humrep/dew271. PMID 27836978. 
  13. ↑ 13.0 13.1 "NOBOX homeobox mutation causes premature ovarian failure". American Journal of Human Genetics 81 (3): 576–81. September 2007. doi:10.1086/519496. PMID 17701902. 
  14. ↑ "Inheritance in idiopathic premature ovarian failure: analysis of 71 cases". Human Reproduction 13 (7): 1796–800. July 1998. doi:10.1093/humrep/13.7.1796. PMID 9740426. 
  15. ↑ 15.0 15.1 "Incidence of premature ovarian failure". Obstetrics and Gynecology 67 (4): 604–6. April 1986. PMID 3960433. 
  16. ↑ "Primary ovarian insufficiency". Lancet 376 (9744): 911–21. September 2010. doi:10.1016/S0140-6736(10)60355-8. PMID 20708256. 
  17. ↑ "New NOBOX mutations identified in a large cohort of women with primary ovarian insufficiency decrease KIT-L expression". The Journal of Clinical Endocrinology and Metabolism 100 (3): 994–1001. March 2015. doi:10.1210/jc.2014-2761. PMID 25514101. 
  18. ↑ "NOBOX is a strong autosomal candidate gene in Tunisian patients with primary ovarian insufficiency". Clinical Genetics 89 (5): 608–13. May 2016. doi:10.1111/cge.12750. PMID 26848058. 
  19. ↑ "Mutation analysis of NOBOX homeodomain in Chinese women with premature ovarian failure". Fertility and Sterility 91 (4 Suppl): 1507–9. April 2009. doi:10.1016/j.fertnstert.2008.08.020. PMID 18930203. 
  20. ↑ "Mutational analysis of the homeobox region of the human NOBOX gene in Japanese women who exhibit premature ovarian failure" (in en). Fertility and Sterility 83 (6): 1843–4. June 2005. doi:10.1016/j.fertnstert.2004.12.031. PMID 15950662. 
  21. ↑ "GDF9 is transiently expressed in oocytes before follicle formation in the human fetal ovary and is regulated by a novel NOBOX transcript". PLOS ONE 10 (3): e0119819. 2015-03-19. doi:10.1371/journal.pone.0119819. PMID 25790371. Bibcode: 2015PLoSO..1019819B. 
  22. ↑ "NOBOX is a key FOXL2 partner involved in ovarian folliculogenesis". Journal of Molecular Cell Biology 6 (2): 175–7. April 2014. doi:10.1093/jmcb/mju006. PMID 24620032. 
  23. ↑ "R-spondin2, a novel target of NOBOX: identification of variants in a cohort of women with primary ovarian insufficiency". Journal of Ovarian Research 10 (1): 51. July 2017. doi:10.1186/s13048-017-0345-0. PMID 28743298. 

Further reading



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