Characterization of a human homolog (OVOL1) of the Drosophila ovo gene, which maps to chromosome 11q13

Dual role of Ovol2 on the germ cell lineage segregation during gastrulation in mouse embryogenesis

In mammals, primordial germ cells (PGCs), the origin of the germ line, are specified from the epiblast at the posterior region where gastrulation simultaneously occurs, yet the functional relationship between PGC specification and gastrulation remains unclear. Here, we show that OVOL2, a transcription factor conserved across the animal kingdom, balances these major developmental processes by repressing the epithelial-to-mesenchymal transition (EMT) that drives gastrulation and the upregulation of genes associated with PGC specification. Ovol2a, a splice variant encoding a repressor domain, directly regulates EMT-related genes and, consequently, induces re-acquisition of potential pluripotency during PGC specification, whereas Ovol2b, another splice variant missing the repressor domain, directly upregulates genes associated with PGC specification. Taken together, these results elucidate the molecular mechanism underlying allocation of the germ line among epiblast cells differentiating into somatic cells through gastrulation.

This article has an associated ‘The people behind the papers’ interview.

OVOL1/2: Drivers of Epithelial Differentiation in Development, Disease, and Reprogramming

OVOL proteins (OVOL1 and OVOL2), vertebrate homologs of Drosophila OVO, are critical regulators of epithelial lineage determination and differentiation during embryonic development in tissues such as kidney, skin, mammary epithelia, and testis. OVOL can inhibit epithelial-mesenchymal transition and/or can promote mesenchymal-epithelial transition. Moreover, they can regulate the stemness of cancer cells, thus playing an important role during cancer cell metastasis. Due to their central role in differentiation and maintenance of epithelial lineage, OVOL overexpression has been shown to be capable of reprogramming fibroblasts to epithelial cells. Here, we review the roles of OVOL-mediated epithelial differentiation across multiple contexts, including embryonic development, cancer progression, and cellular reprogramming.

Comparative transcriptomic analysis of silkworm Bmovo-1 and wild type silkworm ovary

The detailed molecular mechanism of Bmovo-1 regulation of ovary size is unclear. To uncover the mechanism of Bmovo-1 regulation of ovarian development and oogenesis using RNA-Seq, we compared the transcriptomes of wild type (WT) and Bmovo-1-overexpressing silkworm (silkworm^+Bmovo-1) ovaries. Using a pair-end Illumina Solexa sequencing strategy, 5,296,942 total reads were obtained from silkworm^+Bmovo-1 ovaries and 6,306,078 from WT ovaries. The average read length was about 100 bp. Clean read ratios were 98.79% for silkworm^+Bmovo-1 and 98.87% for WT silkworm ovaries. Comparative transcriptome analysis showed 123 upregulated and 111 downregulated genes in silkworm^+Bmovo-1 ovaries. These differentially expressed genes were enriched in the extracellular and extracellular spaces and involved in metabolism, genetic information processing, environmental information processing, cellular processes and organismal systems. Bmovo-1 overexpression in silkworm ovaries might promote anabolism for ovarian development and oogenesis and oocyte proliferation and transport of nutrients to ovaries by altering nutrient partitioning, which would support ovary development. Excessive consumption of nutrients for ovary development alters nutrient partitioning and deters silk protein synthesis.

OVO-like 1 regulates progenitor cell fate in human trophoblast development

Epithelial barrier integrity is dependent on progenitor cells that either divide to replenish themselves or differentiate into a specialized epithelium. This paradigm exists in human placenta, where cytotrophoblast cells either propagate or undergo a unique differentiation program: fusion into an overlying syncytiotrophoblast. Syncytiotrophoblast is the primary barrier regulating the exchange of nutrients and gases between maternal and fetal blood and is the principal site for synthesizing hormones vital for human pregnancy. How trophoblast cells regulate their differentiation into a syncytium is not well understood. In this study, we show that the transcription factor OVO-like 1 (OVOL1), a homolog of Drosophila ovo, regulates the transition from progenitor to differentiated trophoblast cells. OVOL1 is expressed in human placenta and was robustly induced following stimulation of trophoblast differentiation. Disruption of OVOL1 abrogated cytotrophoblast fusion and inhibited the expression of a broad set of genes required for trophoblast cell fusion and hormonogenesis. OVOL1 was required to suppress genes that maintain cytotrophoblast cells in a progenitor state, including MYC, ID1, TP63, and ASCL2, and bound specifically to regions upstream of each of these genes. Our results reveal an important function of OVOL1 as a regulator of trophoblast progenitor cell fate during human trophoblast development.

Bmovo-1 regulates ovary size in the silkworm, Bombyx mori

The regulation of antagonistic OVO isoforms is critical for germline formation and differentiation in Drosophila. However, little is known about genes related to ovary development. In this study, we cloned the Bombyx mori ovo gene and investigated its four alternatively spliced isoforms. BmOVO-1, BmOVO-2 and BmOVO-3 all had four C2H2 type zinc fingers, but differed at the N-terminal ends, while BmOVO-4 had a single zinc finger. Bmovo-1, Bmovo-2 and Bmovo-4 showed the highest levels of mRNA in ovaries, while Bmovo-3 was primarily expressed in testes. The mRNA expression pattern suggested that Bmovo expression was related to ovary development. RNAi and transgenic techniques were used to analyze the biological function of Bmovo. The results showed that when the Bmovo gene was downregulated, oviposition number decreased. Upregulation of Bmovo-1 in the gonads of transgenic silkworms increased oviposition number and elevated the trehalose contents of hemolymph and ovaries. We concluded that Bmovo-1 was involved in protein synthesis, contributing to the development of ovaries and oviposition number in silkworms.

Ovol2 suppresses cell cycling and terminal differentiation of keratinocytes by directly repressing c-Myc and Notch1

Ovol2 belongs to the Ovo family of evolutionarily conserved zinc finger transcription factors that act downstream of key developmental signaling pathways including Wg/Wnt and BMP/TGF-beta. We previously reported Ovol2 expression in the basal layer of epidermis, where epidermal stem/progenitor cells reside. In this work, we use HaCaT human keratinocytes to investigate the cellular and molecular functions of Ovol2. We show that depletion of Ovol2 leads to transient cell expansion but a loss of cells with long term proliferation potential. Mathematical modeling and experimental findings suggest that both faster cycling and precocious withdrawal from the cell cycle underlie this phenotype. Ovol2 depletion also accelerates extracellular signal-induced terminal differentiation in two- and three-dimensional culture models. By chromatin immunoprecipitation, luciferase reporter, and functional rescue assays, we demonstrate that Ovol2 directly represses two critical downstream targets, c-Myc and Notch1, thereby suppressing keratinocyte transient proliferation and terminal differentiation, respectively. These findings shed light on how an epidermal cell maintains a proliferation-competent and differentiation-resistant state.

C2H2 zinc finger genes of the Gli, Zic, KLF, SP, Wilms' tumour, Huckebein, Snail, Ovo, Spalt, Odd, Blimp-1, Fez and related gene families from Branchiostoma floridae

The C2H2 zinc finger is one of the most common domains encoded by animal genomes and has been implicated in DNA binding as well as protein-protein interactions and RNA binding. Genes encoding C2H2 zinc finger domains include not only well-studied conserved transcription factors such as Gli and Snail but also include a large diversity of more rapidly evolving genes. Here, I focus on the description of amphioxus members of families and super-families of C2H2 zinc finger genes that have been the subject of functional studies in other species, specifically the Gli, Zic, Glis, Snail, Scratch, Krox, Wilms' tumour, Huckebein, SP, KLF, Ovo, Spalt, Blimp-1, Odd and Fez genes. Surveys of the Branchiostoma floridae genome reveal members of all of these groups of genes. Genes are named according to molecular phylogenetic analyses, such that the nomenclature reflects pre-existing gene names in the context of gene families that have descended from a single common ancestral gene in the common ancestor of chordates and insects. In total, this comprises 28 B. floridae C2H2 zinc finger genes, representing at least 15 gene families. For 17 of these genes, expressed sequence tag clusters and associated clone identification codes relating to the B. floridae gene collection are given.

The dual function of ovo/shavenbaby in germline and epidermis differentiation is conserved between Drosophila melanogaster and the olive fruit fly Bactrocera oleae

The olive fruit fly Bactrocera oleae (B. oleae) is a major olive damaging pest in the Mediterranean area. As a first molecular analysis of a developmental gene in this insect, we characterised the ovo/shavenbaby (ovo/svb) gene. In Drosophila, ovo/svb encodes a family of transcription regulators with two distinct functions: ovo is required for female germline differentiation and svb controls morphogenesis of epidermal cells. Here, we report the cloning and characterisation of ovo/svb in B. oleae, showing that the ovo genomic organisation and complex pattern of germline transcription have been conserved between distantly related Dipterae. We further show that B. oleae svb embryonic expression precisely prefigures the pattern of larval trichomes, supporting the conclusion that regulatory changes in svb transcription underlie evolutionary diversification of trichome patterns seen among Dipterae.

Ovol2, a mammalian homolog of Drosophila ovo: gene structure, chromosomal mapping, and aberrant expression in blind-sterile mice

The ovo gene family consists of evolutionarily conserved genes including those cloned from Caenorhabditis elegans, Drosophila melanogaster, mouse, and human. Here we report the isolation and characterization of mouse Ovol2 (also known as movol2 or movo2) and provide evidence supporting the existence of multiple Ovol2 transcripts. These transcripts are produced by alternative promoter usage and alternative splicing and encode long and short OVOL2 protein isoforms, whose sequences differ from those previously reported. Mouse and human OVOL2 genes are expressed in overlapping tissues including testis, where Ovol2 expression is developmentally regulated and correlates with the meiotic/postmeiotic stages of spermatogenesis. Mouse Ovol2 maps to chromosome 2 in a region containing blind-sterile (bs), a spontaneous mutation that causes spermatogenic defects and germ cell loss. No mutation has been detected in the coding region of Ovol2 from bs mice, but Ovol2 transcription was dramatically reduced in testes from these mice, suggesting that Ovol2 is expressed in male germ cells.

A germline-specific splicing generates an extended ovo protein isoform required for Drosophila oogenesis

Most regulatory genes are employed multiple times to control different processes during development. The Drosophila Ovo/Shavenbaby (Svb) transcription factor is required both for germline and epidermal differentiation, two roles also found for its ortholog m-ovo1 in mice. In Drosophila, these two distinct functions are contributed by separate control regions directing the expression of Ovo/Svb in the germline (ovo) and soma (svb), respectively. We report here that alternative splicing represents an additional level of the regulation of Ovo/Svb functional specificity. Characterization of the ovo(D1rv23) mutation revealed that the intragenic insertion of a novel retrotransposon, romano, inactivates ovo without altering svb. We provide evidence that this insertion disrupts a germline-specific alternative exon, exon 2b, which encodes a 178-amino-acid internal extension (2B). While both isoforms, Ovo+2B and Ovo-2B, accumulate during oogenesis, only Ovo+2B is able to fulfill germinal ovo functions. Ovo-2B is unable, even when overexpressed, to fully rescue oogenic defects resulting from the absence of wild type ovo product. By contrast, either Ovo+2B or Ovo-2B germline protein can substitute for Svb in the epidermis. Our results emphasize the specific features of splicing in the germline, and reveal its functional importance for the control of ovo/svb-dependent ovarian and epidermal differentiation.

The LEF1/beta -catenin complex activates movo1, a mouse homolog of Drosophila ovo required for epidermal appendage differentiation

Drosophila ovo/svb (dovo) is required for epidermal cuticle/denticle differentiation and is genetically downstream of the wg signaling pathway. Similarly, a mouse homolog of dovo, movo1, is required for the proper formation of hair, a mammalian epidermal appendage. Here, we provide biochemical evidence that movo1 encodes a nuclear DNA binding protein (mOvo1a) that binds to DNA sequences similar to those that dOvo binds to, further supporting the notion that mOvo1a and dOvo are genetically and biochemically homologous proteins. Additionally, we show that the movo1 promoter is activated by the lymphoid enhancer factor 1 (LEF1)/beta-catenin complex, a transducer of wnt signaling. Collectively, our findings suggest that movo1 is a developmental target of wnt signaling during hair morphogenesis in mice, and that the wg/wnt-ovo link in epidermal appendage regulatory pathways has been conserved between mice and flies.

Drosophila OVO regulates ovarian tumor transcription by binding unusually near the transcription start site

Evolutionarily conserved ovo loci encode developmentally regulated, sequence-specific, DNA-binding, C(2)H(2)-zinc-finger proteins required in the germline and epidermal cells of flies and mice. The direct targets of OVO activity are not known. Genetic experiments suggest that ovo acts in the same regulatory network as ovarian tumor (otu), but the relative position of these genes in the pathway is controversial. Three OVO-binding sites exist in a compact regulatory region that controls germline expression of the otu gene. Interestingly, the strongest OVO-binding site is very near the otu transcription start, where basal transcriptional complexes must function. Loss-of-function, gain-of-function and promoter swapping constructs demonstrate that OVO binding near the transcription start site is required for OVO-dependent otu transcription in vivo. These data unambiguously identify otu as a direct OVO target gene and raise the tantalizing possibility that an OVO site, at the location normally occupied by basal components, functions as part of a specialized core promoter.

OVO transcription factors function antagonistically in the Drosophila female germline

OVO controls germline and epidermis differentiation in flies and mice. In the Drosophila germline, alternative OVO-B and OVO-A isoforms have a common DNA-binding domain, but different N-termini. We show that these isoforms are transcription factors with opposite regulatory activities. Using yeast one-hybrid assays, we identified a strong activation domain within a common region and a counteracting repression domain within the OVO-A-specific region. In flies, OVO-B positively regulated the ovarian tumor promoter, while OVO-A was a negative regulator of the ovarian tumor and ovo promoters. OVO-B isoforms supplied ovo(+) function in the female germline and epidermis, while OVO-A isoforms had dominant-negative activity in both tissues. Moreover, elevated expression of OVO-A resulted in maternal-effect lethality while the absence of OVO-A resulted in maternal-effect sterility. Our data indicate that tight regulation of antagonistic OVO-B and OVO-A isoforms is critical for germline formation and differentiation.

Characterization of Drosophila OVO protein DNA binding specificity using random DNA oligomer selection suggests zinc finger degeneration

The Drosophila melanogaster ovo locus codes for several tissue- and stage-specific proteins that all possess a common C-terminal array of four C(2)H(2)zinc fingers. Three fingers conform to the motif framework and are evolutionarily conserved; the fourth diverges considerably. The ovo genetic function affects germ cell viability, sex identity and oogenesis, while the overlapping svb function is a key selector for epidermal structures under the control of wnt and EGF receptor signaling. We isolated synthetic DNA oligomers bound by the OVO zinc finger array from a high complexity starting population and derived a statistically significant 9 bp long DNA consensus sequence, which is nearly identical to a consensus derived from several Drosophila genes known or suspected of being regulated by the ovo function in vivo. The DNA consensus recognized by Drosophila OVO protein is atypical for zinc finger proteins in that it does not conform to many of the 'rules' for the interaction of amino acid contact residues and DNA bases. Additionally, our results suggest that only three of the OVO zinc fingers contribute to DNA-binding specificity.

The ovo gene required for cuticle formation and oogenesis in flies is involved in hair formation and spermatogenesis in mice

The Drosophila svb/ovo gene gives rise to differentially expressed transcripts encoding a zinc finger protein. svb/ovo has two distinct genetic functions: shavenbaby (svb) is required for proper formation of extracellular projections that are produced by certain epidermal cells in late-stage differentiation; ovo is required for survival and differentiation of female germ cells. We cloned a mouse gene, movo1 encoding a nuclear transcription factor that is highly similar to its fly counterpart in its zinc-finger sequences. In mice, the gene is expressed in skin, where it localizes to the differentiating cells of epidermis and hair follicles, and in testes, where it is present in spermatocytes and spermatids. Using gene targeting, we show that movo1 is required for proper development of both hair and sperm. movo1(-/-) mice are small, produce aberrant hairs, and display hypogenitalism, with a reduced ability to reproduce. These mice also develop abnormalities in kidney, where movo1 is also expressed. Our findings reveal remarkable parallels between mice and flies in epidermal appendage formation and in germ-cell maturation. Furthermore, they uncover a phenotype similar to that of Bardet-Biedl syndrome, a human disorder that maps to the same locus as human ovo1.

Identification and characterization of the multiple endocrine neoplasia type 1 (MEN1) gene

For nearly a decade since the mapping of the multiple endocrine neoplasia type 1 (MEN1) locus to 11q13 and the suggestion that it is a tumour suppressor gene, efforts have been made to identify the gene responsible for this familial cancer syndrome. Recently, we have identified the MEN1 gene by the positional cloning approach. This effort involved construction of a 2.8-Mb physical map (D11S480-D11S913) based primarily on a bacterial clone contig. Using these resources, 20 new polymorphic markers were isolated which helped to reduce the interval for candidate genes by haplotype analysis in families and by loss of heterozygosity (LOH) studies in approximately 200 tumours, utilizing laser-assisted microdissection to obtain tumour cells with minimal or no admixture by normal cells. The interval was narrowed by LOH to only 300 kb, and nearly 20 new transcripts that map to this region of 11q13 were isolated and characterized. One of the transcripts was found by dideoxyfingerprinting and cycle sequencing to harbour deleterious germline mutations in affected individuals from MEN-1 kindreds and therefore identified as the MEN1 gene. The type of germline mutations and the identification of mutations in sporadic tumours support the Knudson's two-hit model of tumorigenesis for MEN-1. Efforts are being made to identify the function of the MEN1 gene-encoded protein, menin, and to study its role in tumorigenesis.