The heterochronic gene lin-29 encodes a zinc finger protein that controls a terminal differentiation event in Caenorhabditis elegans

Heterochronic genes control cell cycle progress and developmental competence of C. elegans vulva precursor cells

Heterochronic genes control the timing of vulval development in the C. elegans hermaphrodite. lin-14 or lin-28 loss-of-function mutations cause the vulval precursor cells (VPCs) to enter S phase and to divide one larval stage earlier than in the wild type. A precocious vulva is formed by essentially normal cell lineage patterns, governed by the same intercellular signals as in the wild type. Mutations that prevent the normal developmental down-regulation of lin-14, activity delay or block VPC division and prevent vulval differentiation. A genetic pathway that includes lin-4, lin-14, and lin-28 controls when VPCs complete G1 and also controls when VPCs acquire the competence to respond to the intercellular patterning signals and express vulval fates.

Vertebrate neural progenitor cells: subtypes and regulation

Several advances have been made recently in characterizing neural progenitor cells. In vertebrates, multipotential stem cells have been demonstrated in the developing forebrain both in vitro and in vivo, and a class of stem cells has been identified in the adult CNS. Factors that regulate the proliferation and differentiation of subtypes of neural progenitor cells have also been described. In invertebrates, progress has been made in identifying genes involved in neural progenitor cell specification, cell-fate choices and regulation.

The Caenorhabditis elegans heterochronic gene pathway controls stage-specific transcription of collagen genes

In Caenorhabditis elegans, the terminal differentiation of the hypodermal cells occurs at the larval-to-adult molt, and is characterized in part by the formation of a morphologically distinct adult cuticle. The timing of this event is controlled by a pathway of heterochronic genes that includes the relatively direct regulatory gene, lin-29, and upstream genes lin-4, lin-14 and lin-28. Using northern analysis to detect endogenous collagen mRNA levels and collagen/lacZ reporter constructs to monitor collagen transcriptional activity, we show that the stage-specific switch from larval cuticle to adult cuticle correlates with the transcriptional activation of adult-specific collagen genes and repression of larval-specific collagen genes. Heterochronic mutations that cause precocious formation of adult cuticle also cause precocious transcription of the adult-specific collagen genes, col-7 and col-19; heterochronic mutations that prevent the switch to adult cuticle cause continued expression of the larval collagen gene, col-17, in adults and prevent adult-specific activation of col-7 or col-19. A 235 bp segment of col-19 5′ sequences is sufficient to direct the adult-specific expression of a col-19/lacZ reporter gene in hypodermal cells. These findings indicate that the heterochronic gene pathway regulates the timing of hypodermal cell terminal differentiation by regulating larval- and adult-specific gene expression, perhaps by the direct action of lin-29.