Regulation of cell fate in Caenorhabditis elegans by a novel cytoplasmic polyadenylation element binding protein

Musashi: a translational regulator of cell fate

Transcription is thought to have a major role in the regulation of cell fate; the importance of translational regulation in this process has been less certain. Recent findings demonstrate that translational regulation contributes to cell-fate specification. The evolutionarily conserved, neural RNA-binding protein Musashi, for example, controls neural cell fate. The protein functions in maintenance of the stem-cell state, differentiation, and tumorigenesis by repressing translation of particular mRNAs. In mammals it might play an important role in activating Notch signalling by repressing translation of the Notch inhibitor m-Numb.

Turning clustering loops: sex determination in Caenorhabditis elegans

The nematode Caenorhabditis elegans has two sexes: males and hermaphrodites. Hermaphrodites are essentially female animals that produce sperm and oocytes. In the past few years tremendous progress has been made towards understanding how sexual identity is controlled in the worm. These analyses have revealed that the regulatory pathway controlling sexual development is far from linear and that it contains a number of loops and branches that play crucial roles in regulating sexual development. This review summarizes our current understanding of the mechanisms that regulate sexual cell fate in C. elegans.

In Caenorhabditis elegans, the RNA-binding domains of the cytoplasmic polyadenylation element binding protein FOG-1 are needed to regulate germ cell fates

FOG-1 controls germ cell fates in the nematode Caenorhabditis elegans. Sequence analyses revealed that FOG-1 is a cytoplasmic polyadenylation element binding (CPEB) protein; similar proteins from other species have been shown to bind messenger RNAs and regulate their translation. Our analyses of fog-1 mutations indicate that each of the three RNA-binding domains of FOG-1 is essential for activity. In addition, biochemical tests show that FOG-1 is capable of binding RNA sequences in the 3'-untranslated region of its own message. Finally, genetic assays reveal that fog-1 functions zygotically, that the small fog-1 transcript has no detectable function, and that missense mutations in fog-1 cause a dominant negative phenotype. This last observation suggests that FOG-1 acts in a complex, or as a multimer, to regulate translation. On the basis of these data, we propose that FOG-1 binds RNA to regulate germ cell fates and that it does so by controlling the translation of its targets. One of these targets might be the fog-1 transcript itself.

Specification of germ cell fates by FOG-3 has been conserved during nematode evolution

Rapid changes in sexual traits are ubiquitous in evolution. To analyze this phenomenon, we are studying species of the genus Caenorhabditis. These animals use one of two different mating systems-male/hermaphroditic, like the model organism Caenorhabditis elegans, or male/female, like C. remanei. Since hermaphrodites are essentially females that produce sperm for self-fertilization, elucidating the control of cell fate in the germ line in each species could provide the key to understanding how these mating systems evolved. In C. elegans, FOG-3 is required to specify that germ cells become sperm. Thus, we cloned its homologs from both C. remanei and C. briggsae. Each species produces a single homolog of FOG-3, and RNA-mediated interference indicates that FOG-3 functions in each species to specify that germ cells develop as sperm rather than as oocytes. What factors account for the different mating systems? Northern analyses and RT-PCR data reveal that the expression of fog-3 is always correlated with spermatogenesis. Since the promoters for all three fog-3 genes contain binding sites for the transcription factor TRA-1A and are capable of driving expression of fog-3 in C. elegans hermaphrodites, we propose that alterations in the upstream sex-determination pathway, perhaps acting through TRA-1A, allow spermatogenesis in C. elegans and C. briggsae XX larvae but not in C. remanei.

It ain't over till it's ova: germline sex determination in C. elegans

Sex determination in most organisms involves a simple binary fate choice between male or female development; the outcome of this decision has profound effects on organismal biology, biochemistry and behaviour. In the nematode C. elegans, there is also a binary choice, either male or hermaphrodite. In C. elegans, distinct genetic pathways control somatic and germline sexual cell fate. Both pathways share a common set of globally acting regulatory genes; however, germline-specific regulatory genes also participate in the decision to make male or female gametes. The determination of sexual fate in the germline of the facultative hermaphrodite poses a special problem, because first sperm then oocytes are produced. It has emerged that additional layers of post-transcriptional regulation have been imposed to modulate the activities of the global sex-determining genes, tra-2 and fem-3; the balance between these activities is crucial in controlling sexual cell fate in the hermaphrodite germline.