In a microarray-based gene profiling analysis of Mü ller glia-derived retinal stem cells in light-damaged retinas from adult zebrafish, we found that 2 genes required for regeneration of fin and heart tissues in zebrafish, hspd1 (heat shock 60-kDa protein 1) and mps1 (monopolar spindle 1), were up-regulated. Expression of both genes in the neurogenic Mü ller glia and progenitors was independently verified by quantitative reverse transcriptase PCR and in situ hybridization. Functional analysis of temperature-sensitive mutants of hspd1 and mps1 revealed that both are necessary for Mü ller glia-based cone photoreceptor regeneration in adult zebrafish retina. In the amputated fin, hspd1 is required for the induction of mesenchymal stem cells and blastema formation, whereas mps1 is required at a later step for rapid cell proliferation and outgrowth. This temporal sequence of hspd1 and mps1 function is conserved in the regenerating retina. Comparison of gene expression profiles from regenerating zebrafish retina, caudal fin, and heart muscle revealed additional candidate genes potentially implicated in injury-induced epimorphic regeneration in diverse zebrafish tissues.T he study of regeneration has long fascinated biologists and has lately experienced a renaissance associated with growing interest in regenerative medicine and the therapeutic potential of stem cells. Zebrafish (Danio rerio) are an ideal genetic model for studying regeneration in vertebrates (1) because they have remarkable capabilities to regenerate fins (2), heart muscle (3), and nervous tissues (4-7) following injury. A forward mutagenesis screen for temperature-sensitive mutations that interfere with regeneration of amputated caudal fin identified several genes whose functions are critical for specific steps in fin regeneration, including mps1 (monopolar spindle 1, also called ttk, a kinase required for mitotic checkpoint regulation), hspd1 (heat shock 60-kDa protein 1, a mitochondrial chaperone), and fgf20 (fibroblast growth factor 20) (8-10). In addition, gene profiling analysis of regenerating tissues has provided lists of candidate genes associated with regeneration in fin (11), heart (12), and neural retina (13-15).The regeneration of retinal neurons in adult zebrafish is an especially powerful model for studying regeneration of neuronal tissues; laminar retinal architecture and visual function are restored following damage inflicted by surgical lesions, neurotoxins, and laser or photic lesions of retina (16). The neural stem cells in the retina arise from differentiated Müller glia, which respond to local retinal injuries by dedifferentiation, proliferation, and production of multipotent neuronal progenitors (retinal stem cells) that can regenerate all types of retinal neurons (17-19). To discover genes expressed in injury-activated neurogenic Müller glial cells that activate stem cell properties and trigger a neurogenic program, we generated transcriptional profiles of isolated fluorescent-tagged Müller glial cells from light-lesioned adult ...

Müller glia are the resident radial glia in the vertebrate retina. The response of mammalian Müller glia to retinal damage often results in a glial scar and no functional replacement of lost neurons. Adult zebrafish Müller glia, in contrast, are considered tissue-specific stem cells that can self-renew and generate neurogenic progenitors to regenerate all retinal neurons after damage. Here, we demonstrate that regulation of TGFβ signaling by the corepressors Tgif1 and Six3b is critical for the proliferative response to photoreceptor destruction in the adult zebrafish retina. When function of these corepressors is disrupted, Müller glia and their progeny proliferate less, leading to a significant reduction in photoreceptor regeneration. Tgif1 expression and regulation of TGFβ signaling are implicated in the function of several types of stem cells, but this is the first demonstration that this regulatory network is necessary for regeneration of neurons.

Stem cells maintain tissues and organs over the lifespan of individuals. How aging influences this process is unclear. Here we investigate the effects of aging on C. elegans germline stem/progenitor cells and show that the progenitor pool is depleted over time in a manner dependent on inhibition of DAF-16/FOXO by insulin/IGF-1 signalling (IIS). Our data indicate that DAF-16/FOXO activity in certain somatic gonad cells is required for germline progenitor maintenance, and that this role is separable from the effect of DAF-16/FOXO on organismal aging. In addition, blocking germ cell flux, similar to reducing IIS, maintains germline progenitors. This effect is partially dependent on gonadal DAF-16/FOXO activity. Our results imply that (1) longevity pathways can regulate aging stem cells through anatomically separable mechanisms, (2) stem cell maintenance is not necessarily prioritized and (3) stem cell regulation can occur at the level of an entire organ system such as the reproductive system.

Fgf signaling is required for many biological processes involving the regulation of cell proliferation and maintenance, including embryonic patterning, tissue homeostasis, wound healing, and cancer progression. Although the function of Fgf signaling is suggested in several different regeneration models, including appendage regeneration in amphibians and fin and heart regeneration in zebrafish, it has not yet been studied during zebrafish photoreceptor cell regeneration. Here we demonstrate that intravitreal injections of FGF-2 induced rod precursor cell proliferation and photoreceptor cell neuroprotection during intense light damage. Using the dominant-negative Tg(hsp70:dn-fgfr1) transgenic line, we found that Fgf signaling was required for homeostasis of rod, but not cone, photoreceptors. Even though fgfr1 is expressed in both rod and cone photoreceptors, we found that Fgf signaling differentially affected the regeneration of cone and rod photoreceptors in the light-damaged retina, with the dominant-negative hsp70:dn-fgfr1 transgene significantly repressing rod photoreceptor regeneration without affecting cone photoreceptors. These data suggest that rod photoreceptor homeostasis and regeneration is Fgf-dependent and that rod and cone photoreceptors in adult zebrafish are regulated by different signaling pathways.

The Caenorhabditis elegans germ line is an outstanding model system in which to study the control of cell division and differentiation. Although many of the molecules that regulate germ cell proliferation and fate decisions have been identified, how these signals interact with cellular dynamics and physical forces within the gonad remains poorly understood. We therefore developed a dynamic, 3D in silico model of the C. elegans germ line, incorporating both the mechanical interactions between cells and the decision-making processes within cells. Our model successfully reproduces key features of the germ line during development and adulthood, including a reasonable ovulation rate, correct sperm count, and appropriate organization of the germ line into stably maintained zones. The model highlights a previously overlooked way in which germ cell pressure may influence gonadogenesis, and also predicts that adult germ cells might be subject to mechanical feedback on the cell cycle akin to contact inhibition. We provide experimental data consistent with the latter hypothesis. Finally, we present cell trajectories and ancestry recorded over the course of a simulation. The novel approaches and software described here link mechanics and cellular decision-making, and are applicable to modeling other developmental and stem cell systems.