Mutations in the human SIX3 gene in holoprosencephaly are loss of function.
Holoprosencephaly (HPE) is the most common developmental anomaly of the human forebrain; however, the genetics of this heterogeneous and etiologically complex malformation is incompletely understood. Heterozygous mutations in SIX3, a transcription factor gene expressed in the anterior forebrain and eyes during early vertebrate development, have been frequently detected in human HPE cases. However, only a few mutations have been investigated with limited functional studies that would confirm a role in HPE pathogenesis. Here, we report the development of a set of robust and sensitive assays of human SIX3 function in zebrafish and apply these to the analysis of a total of 46 distinct mutations (19 previously published and 27 novel) located throughout the entire SIX3 gene. We can now confirm that 89% of these putative deleterious mutations are significant loss-of-function alleles. Since disease-associated single point mutations in the Groucho-binding eh1-like motif decreases the function in all assays, we can also confirm that this interaction is essential for human SIX3 co-repressor activity; we infer, in turn, that this function is important in HPE causation. We also unexpectedly detected truncated versions with partial function, yet missing a SIX3-encoded homeodomain. Our data indicate that SIX3 is a frequent target in the pathogenesis of HPE and demonstrate how this can inform the genetic counseling of families.
Domené
Sabina
S
1Medical Genetics Branch, National Human Genome Research Institute, Bethesda, MD 20892, USA.
Roessler
Erich
E
El-Jaick
Kenia B
KB
Snir
Mirit
M
Brown
Jamie L
JL
Vélez
Jorge I
JI
Bale
Sherri
S
Lacbawan
Felicitas
F
Muenke
Maximilian
M
Feldman
Benjamin
B
D000483:Alleles; D020816:Amino Acid Motifs / Q000235:genetics; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D004252:DNA Mutational Analysis; D005136:Eye Proteins / Q000235:genetics* / Q000502:physiology; D016142:Holoprosencephaly / Q000209:etiology / Q000235:genetics* / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000235:genetics* / Q000502:physiology; D006801:Humans; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000502:physiology; D017354:Point Mutation / Q000235:genetics*; D015027:Zebrafish / Q000196:embryology / Q000235:genetics / Q000378:metabolism; D000097607:Homeobox Protein SIX3
D005136:Eye Proteins; D018398:Homeodomain Proteins; D009419:Nerve Tissue Proteins; D000097607:Homeobox Protein SIX3
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