piwi encodes a product involved in stem cell renewal. The piwi function is required both to maintain germline stem cells and subsequently for the division and differentiation of the stem cell progeny in both sexes. piwi has a cell autonomous function in promoting stem cell division in the germline. piwi gene product affects the asymmetric division of the male and female germline stem cell (GSC).
piwi mediates a somatic signaling mechanism required for the asymmetric division of germ-line stem cells to produce and maintain a daughter germ-line stem cell but is not essential for the further differentiation of the committed daughter cell. Cox et al(1998) . piwi has a cell autonomous function in promoting stem cell division in the germline. Cox et al(2000) .
piwi belongs to a gene family with members required for RNAiPal-Bhadra et al (2002).
NCBI Summary:
This gene encodes a member of the PIWI subfamily of Argonaute proteins, evolutionarily conserved proteins containing both PAZ and Piwi motifs that play important roles in stem cell self-renewal, RNA silencing, and translational regulation in diverse organisms. The encoded protein may play a role as an intrinsic regulator of the self-renewal capacity of germline and hematopoietic stem cells. Alternatively spliced transcript variants encoding different isoforms have been found for this gene. [provided by RefSeq, Jul 2010]
PAZ domain
Piwi domain
belongs to a gene family with members required for RNAiPal-Bhadra et al (2002).
Cellular localization
Nuclear
Comment
Ovarian function
Oogenesis, stem cell renewal, cyst formation
Comment
Expression regulated by
Comment
Ovarian localization
Oocyte, stem cells, cytoblast, cyst
Comment
Piwi Proteins and piRNAs in Mammalian Oocytes and Early Embryos. Roovers EF et al. (2015) Germ cells of most animals critically depend on piRNAs and Piwi proteins. Surprisingly, piRNAs in mouse oocytes are relatively rare and dispensable. We present compelling evidence for strong Piwi and piRNA expression in oocytes of other mammals. Human fetal oocytes express PIWIL2 and transposon-enriched piRNAs. Oocytes in adult human ovary express PIWIL1 and PIWIL2, whereas those in bovine ovary only express PIWIL1. In human, macaque, and bovine ovaries, we find piRNAs that resemble testis-borne pachytene piRNAs. Isolated bovine follicular oocytes were shown to contain abundant, relatively short piRNAs that preferentially target transposable elements. Using label-free quantitative proteome analysis, we show that these maturing oocytes strongly and specifically express the PIWIL3 protein, alongside other, known piRNA-pathway components. A piRNA pool is still present in early bovine embryos, revealing a potential impact of piRNAs on mammalian embryogenesis. Our results reveal that there are highly dynamic piRNA pathways in mammalian oocytes and early embryos./////////////////Identification of PIWIL1 Isoforms and Their Expression in Bovine Testes, Oocytes, and Early Embryos. Russell SJ et al. (2016) PIWI proteins are members of the larger Argonaute family and bind to specific 24-32 nucleotide (nt) RNAs called PIWI-interacting RNAs (piRNAs). piRNAs direct PIWI-mediated suppression of retrotransposon expression in the male germline in humans and mice but their roles in bovine reproduction and embryogenesis are unknown. Although the majority of research in mammals has focused on the functions of PIWI proteins during spermatogenesis, this family of proteins and their associated piRNAs have recently been identified in early embryos. The goals of this study were to characterize the expression of PIWIL1 in bovine testis, oocytes and early embryos. A full-length PIWIL1 transcript and protein was found in the testis, specifically in the germs cells of mature seminiferous tubules. RNA-immunoprecipitation demonstrated the presence of putative piRNAs with a mean length of 30 nt bound to PIWIL1 in testes. 3'RACE analysis of PIWIL1 transcripts in testes and oocytes revealed two shorter isoforms in addition to the full-length transcript which was only present in testes. Truncated PIWIL1 isoforms in oocytes and testes were confirmed through amplification of their unique intronic fragments. Expression profiling of PIWIL1 through early embryogenesis demonstrated peak mRNA expression at the 2-cell stage with decreasing levels through to the blastocyst. PIWIL1-YFP fusion plasmids were produced for each isoform and expressed in HEK 293 cells, demonstrating nuclear exclusion and size specific banding of the different isoforms. These data represent the first comprehensive characterization of PIWIL1 in the bovine, reveal the functional similarities with PIWIL1 in other species and suggest tissue specific expression of several isoforms.//////////////////
Follicle stages
oogenesis, cyst
Comment
Phenotypes
Mutations
2 mutations
Species: D. melanogaster
Mutation name: None
type: None fertility: infertile - ovarian defect Comment: Mutant males show severe defects in spermatogenesis. In female mutant, ovarioles are almost completely devoid of germline cells. Female germ-line stem cells are of normal number but are mispositioned in third instar ovaries. Number of ovariole in most adult ovaries is within the normal range. Germ line stem cells differentiate without self-renewing divisions immediately following the initiation of oogenesis. Germ line stem cells and cystoblasts are undetectable in mutant ovaries, as indicated by the absence of spectrosome-containing germ cells. Most ovaries contain differentiated germ-line cysts whose number approximately equals that of the germ line stem cells. Cysts are much larger in size and contain two- to multicell stage fusomes, indicating their differentiated state. Adult ovaries contain only 2 normal or abnormal egg chambers connected to a germarium lacking other germ line cells.Somatic clonal analysis reveals that piwi function is not required in follicle cells for egg chamber development. Cox et al(1998)
Homozygous females do not lay eggs. The small number of eggs that they do produce are retained in the ovary and eventually atrophy. Homozygous germline stem cells (GSCs) (induced by mitotic recombination immediately prior to oogenesis) are present three weeks following oogenesis. The homozygous GSCs divide four-fold slower than their wild-type counterparts.
Species: other
Mutation name: type: null mutation fertility: infertile - ovarian defect Comment: A Role for Piwi and piRNAs in Germ Cell Maintenance and Transposon Silencing in Zebrafish. Houwing S et al. Piwi proteins specify an animal-specific subclass of the Argonaute family that, in vertebrates, is specifically expressed in germ cells. We demonstrate that zebrafish Piwi (Ziwi) is expressed in both the male and the female gonad and is a component of a germline-specifying structure called nuage. Loss of Ziwi function results in a progressive loss of germ cells due to apoptosis during larval development. In animals that have reduced Ziwi function, germ cells are maintained but display abnormal levels of apoptosis in adults. In mammals, Piwi proteins associate with approximately 29-nucleotide-long, testis-specific RNA molecules called piRNAs. Here we show that zebrafish piRNAs are present in both ovary and testis. Many of these are derived from transposons, implicating a role for piRNAs in the silencing of repetitive elements in vertebrates. Furthermore, we show that piRNAs are Dicer independent and that their 3' end likely carries a 2'O-Methyl modification.