Sp (specificity protein) transcription factors are important regulators of many cellular processes, such as cell cycle, metabolism and morphogenesis. The Sp family is united by a specific combination of three conserved Cys2His2 zinc fingers that form the DNA-binding domain and a Buttonhead (BTD) box CXCPXC, just N-terminal to the zinc fingers. There are nine Sp genes both in humans and in mice. C. elegans has three Sp-related transcription factors:
sptf-1,
sptf-2 and
sptf-3. Our aim is to characterize the functions of these three transcription factors and to find some of their interacting partners. Therefore we have made GFP fusion constructs to determine their expression patterns and we set out to analyze the phenotypes of knockout, knockdown and transgenic animals carrying additional copies of a particular sptf-gene. The gene structure of
spft-1 has been confirmed previously.
sptf-1::GFP expression is first observed in late embryos; from L1 to adult GFP is expressed in the intestine, rectum, 3 neurons in the head and from L3 onwards in the vulva.
sptf-1(
tm784) knockout animals are homozygous viable, but with a low rate of survival until adulthood. We rescued the phenotype in knockout animals by injecting a low dose of
sptf-1. RNAi experiments show no obvious phenotype. High level of overexpression of
sptf-1, sptf-1XS, caused effects on movement and body morphology.
sptf-2 gene structure has been confirmed.
sptf-2 is expressed post embryonically in the intestine, body muscles, and two neurons in the head.
sptf-2(
tm1130) knockouts are viable, no obvious phenotype was observed. RNAi experiments show no obvious phenotype. High levels of
sptf-2 overexpression is probably lethal since F1 sptf-2XS animals did not produce viable transgenic progeny. We have identified two splice forms of
sptf-3, one confirms the prediction, the second splice variant has three additional upstream exons.
sptf-3::GFP is expressed ubiquitously in early embryos and at the comma stage; from late embryos to adults GFP is restricted to the intestine, neurons of the ventral and dorsal nerve cords as well as two neurons in the head close to the posterior pharyngeal bulb.
sptf-3(
tm607) knockout animals are lethal, 20% embryonically, 77% as L1, 3% as L2. RNAi screens of
sptf-3 show a spectrum of mutant phenotypes, comprising embryonic lethality, maternal sterility, abnormal both body morphology and locomotory behaviour. We have observed growth defects in sptf-3XS transgenic animals. Currently we are setting up a screen to identify suppressors of sptf-induced lethality.