Development of the Drosophila R7 photoreceptor is dependent on the 'seven in absentia' (sina)
gene. Hu et al. (1997) characterized 2 highly conserved human homologs of sina, termed SIAH1 and SIAH2. Independent
studies have shown that Sina and its highly related mammalian homologues Siah-1
and Siah-2 bind to the DCC (deleted in colorectal cancer) protein and promote its
proteolysis via the ubiquitin-proteasome pathway.(Hu et al 1999) .
The sina protein is nuclear localizing and required downstream of
Ras1, Raf and the tyrosine kinase sevenless in Drosophila. Recent results have demonstrated a high degree of functional conservation between vertebrate and
insect tyrosine kinase signalling pathways, involving such proteins as Son of sevenless, Grb2 and GAP. These findings, together with the high degree of
sequence conservation between the Siah proteins and sina, suggest that the
mammalian Siah proteins may also participate in signal transduction by some
tyrosine kinases.
Cellular localization
Cytoplasmic, Nuclear
Comment
Ovarian function
Oogenesis
Comment
Expression regulated by
Comment
Ovarian localization
Oocyte
Comment
Follicle stages
Primary, Secondary, Antral, Preovulatory
Comment
Della NG, et al 1995 reported the expression of Siah-2, a vertebrate homologue of Drosophila sina,
in germ cells of the mouse ovary and testis.
Siah-2 is one of three murine homologues of the Drosophila gene seven in
absentia (sina). They report a high level of expression of Siah-2 in a specific
population of germ cells within both the mouse ovary and testis. Siah-2 expression
was absent in primordial oocytes but was detected in all growing oocytes,
coincident with their recruitment from the pool of quiescent cells. The level of
Siah-2 mRNA increased as the oocytes matured and was readily detectable in
Graafian follicles and in fertilized zygotes up until the two cell stage, a time of
extensive maternal transcript degradation and zygotic gene activation. The expression pattern of Siah-2 in germ cells
was similar to that described for the proto-oncogene c-mos.