Y Chromosome
Introduction
Humans have 23 pairs of chromosomes, 22 autosomes and a pair of sex chromosomes. Males have one X and one Y chromosomes (46, XY) and females have a pair of X chromosomes (46, XX). The Y chromosome is much smaller than the X chromosome and contains 50 million base pairs encoding approximately 200+ genes. The Sry gene, found in 1990, encodes is responsible for male sex determination. SRY mutations lead to XY sex reversal in humans, and XX mice with an SRY transgene develop as fertile males. Interestingly, the laboratory rat, Rattus norvegicus, has at least 6 full length copies of the Sry gene.[1]
The male-specific region of the human Y chromosome was originally called the non-recombining portion of the Y chromosome (NRY). This region consists of three different classes of euchromatic sequences:
- X-transposed
- X-degenerate
- ampliconic sequences
Some Recent Findings
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Male Sex Determination
Sry (sex-determining region on the Y chromosome) gene was found in 1990 on the Y chromosome and the first Sox gene identified, the sry gene encodes a "testis-determining factor" a 204aa protein (Mr 23884 Da).
Sry acts as a transcriptional activator (HMG type-high mobility group) binding to DNA and initiating male sex determination then regulating male development. The protein sequence is shown on this current page and the full genebank entry can also be seen. The sry protein has a HMG box that binds DNA by intercalating in the minor groove. Read about the mapping of the testis determining factor which is SRY.
The actual gene targets of SRY are still being determined but at least one downstream gene Sox9 has been identified. Another gene Dax1 (nuclear hormone-receptor superfamily member) when expressed as a transgene will antagonize Sry and also force dosage-sensitive sex reversal.
Sox
Sox is an acronym of "Sry-related HMG box" and there have now been identified at least eight groups of genes that belong to this family with different functions. (for review see[2]) The "HMG box" is a region that functions for DNA binding, DNA bending, protein interactions, and nuclear import or export.
The high mobility group (HMG) domain is a 79 amino acid protein region.
SRY Nuclear Import
A model for nuclear import of SRY from normal males and XY females. [3]
The distinct nuclear localization signals (NLSs) of SRY use different import pathways.
- cNLS - recognized by IMPβ, docks the transport complex at the nuclear pore complex (NPC) and is then translocation through. After nuclear entry of the complex, RanGTP binds to IMPβ to trigger release of SRY; DNA binding by SRY may also facilitate the release process.
- nNLS - mediates nuclear import through a novel pathway not utilizing conventional nuclear import factors such as IMPs but an unidentified "transport factor" (TF) suggested to be calcium-calmodulin.
Sry Target Genes
Cerebellin 4 precursor (Cbln4) - encodes a secreted protein expressed in Sertoli cells in the developing gonad.[4]
Testis-specific Protein Y Chromosome
Testis-specific Protein Y Chromosome (TSPY) is an ampliconic gene on the Y chromosome with an unknown function, though the protein that has been shown to interact with gonadoblastoma. A recent study suggests that TSPY serves as a repressor in androgen-induced tumor development in testicular germ-cell tumours (TGCTs).[5]
Pseudoautosomal Regions
These are two intervals of sequence identity at the tips of both the Y and X chromosomes, the human pseudoautosomal regions PAR1 and PAR2.[6] Loss of PAR1 has been associated with male sterility. |
References
- ↑ <pubmed>17408480</pubmed>| PMC1852568 | BMC Genet.
- ↑ <pubmed>17625949</pubmed>
- ↑ <pubmed>12764225</pubmed>| PMC165827 | Proc Natl Acad Sci U S A.
- ↑ <pubmed>19211811</pubmed>| PMC2804802 | Biol Reprod.
- ↑ <pubmed>21041627</pubmed>
- ↑ <pubmed>18398439</pubmed>
Online Textbooks
Search NLM Online Textbooks "Y chromosome" : Developmental Biology | Endocrinology | Molecular Biology of the Cell | The Cell- A molecular Approach
Reviews
<pubmed>20005972</pubmed> <pubmed>19699459</pubmed> <pubmed>18062864</pubmed> <pubmed>17237341</pubmed> <pubmed>15949865</pubmed>
Articles
<pubmed>21039604</pubmed> <pubmed>2030730</pubmed> <pubmed>1695712</pubmed>
Search PubMed
Search November 2010 "Y Chromosome" - All (11590) Review (1052) Free Full Text (2688)
Search Pubmed: Y Chromosome | SRY
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Cite this page: Hill, M.A. (2024, June 15) Embryology Y Chromosome. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Y_Chromosome
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G