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Cell-type specific light-mediated transcript regulation in the multicellular alga Volvox carteri.

ABSTRACT: BACKGROUND: The multicellular green alga Volvox carteri makes use of none less than 13 photoreceptors, which are mostly expressed in a cell-type specific manner. This gives reason to believe that trasncriptome pattern of each cell type could change differentially in response to environmental light. Here, the cell-type specific changes of various transcripts from different pathways in response to blue, red and far-red light were analyzed. RESULTS: In response to different light qualities, distinct changes in transcript accumulation of genes encoding proteins involved in chlorophyll and carotenoid biosynthesis, light-harvesting complexes, circadian clock and cell cycle control were observed. Namely, blue light tends to be effective to accumulate transcripts in the somatic cells; while red light leads to accumulate transcripts predominantly in the reproductive cells. Blue light also induced marked accumulation of two components of circadian rhythms only in the somatic cells, indicating that these clock-relevant components are affected by blue light in a cell-type specific manner. Further, we show that photosynthetic associated genes are regulated distinctly among cell types by different light qualities. CONCLUSION: Our results suggest that Volvox uses different sophisticated cell-type specific light signaling pathways to modulate expression of genes involved in various cellular and metabolic pathways including circadian rhythms and photosynthesis in response to environmental light.

SUBMITTER: Kianianmomeni A

PROVIDER: S-EPMC4167131 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature

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Project description:Germ-soma differentiation is a hallmark of complex multicellular organisms, yet its origins are not well understood. Volvox carteri is a simple multicellular green alga that has recently evolved a simple germ-soma dichotomy with only two cell-types: large germ cells called gonidia and small terminally differentiated somatic cells. Here, we provide a comprehensive characterization of the gonidial and somatic transcriptomes of V. carteri to uncover fundamental differences between the molecular and metabolic programming of these cell-types. We found extensive transcriptome differentiation between cell-types, with somatic cells expressing a more specialized program overrepresented in younger, lineage-specific genes, and gonidial cells expressing a more generalist program overrepresented in more ancient genes that shared striking overlap with stem cell-specific genes from animals and land plants. Directed analyses of different pathways revealed a strong dichotomy between cell-types with gonidial cells expressing growth-related genes and somatic cells expressing an altruistic metabolic program geared toward the assembly of flagella, which support organismal motility, and the conversion of storage carbon to sugars, which act as donors for production of extracellular matrix (ECM) glycoproteins whose secretion enables massive organismal expansion. V. carteri orthologs of diurnally controlled genes from C. reinhardtii, a single-celled relative, were analyzed for cell-type distribution and found to be strongly partitioned, with expression of dark-phase genes overrepresented in somatic cells and light-phase genes overrepresented in gonidial cells- a result that is consistent with cell-type programs in V. carteri arising by cooption of temporal regulons in a unicellular ancestor. Together, our findings reveal fundamental molecular, metabolic, and evolutionary mechanisms that underlie the origins of germ-soma differentiation in V. carteri and provide a template for understanding the acquisition of germ-soma differentiation in other multicellular lineages.

Project description:Germ-soma differentiation is a hallmark of complex multicellular organisms, yet its origins are not well understood. Volvox carteri is a simple multicellular green alga that has recently evolved a simple germ-soma dichotomy with only two cell types: large germ cells called gonidia and small terminally differentiated somatic cells. Here, we provide a comprehensive characterization of the gonidial and somatic transcriptomes of Volvox to uncover fundamental differences between the molecular and metabolic programming of these cell types. We found extensive transcriptome differentiation between cell types, with somatic cells expressing a more specialized program overrepresented in younger, lineage-specific genes and gonidial cells expressing a more generalist program overrepresented in more ancient genes that shared striking overlap with metazoan stem-cell-specific genes. Directed analyses of metabolic pathways revealed a strong dichotomy between cell types with gonidial cells expressing growth-related genes and somatic cells expressing an altruistic metabolic program geared towards the assembly of flagella, which support organismal motility, and the conversion of storage carbon to sugars, which act as donors of extracellular matrix glycoproteins whose secretion enables massive organismal expansion. Volvox orthologs of Chlamydomonas diurnally regulated genes were analyzed for cell-type distribution and found to be strongly partitioned, with expression of dark-phase genes overrepresented in somatic cells and light-phase genes overrepresented in gonidial cells, a result that is consistent with cell type programs in Volvox arising by cooption of temporal regulons in a unicellular ancestor. Together our findings reveal fundamental molecular, metabolic, and evolutionary mechanisms that underlie the origins of germ-soma differentiation in Volvox and provide a template for understanding the acquisition of germ-soma differentiation in other multicellular lineages.

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Cell-type specific light-mediated transcript regulation in the multicellular alga Volvox carteri.

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