Chicken spindlin genes on W and Z chromosomes: transcriptional expression of both genes and dynamic behavior of spindlin in interphase and mitotic cells

Simple, sensitive and robust chicken specific sexing assays, compliant with large scale analysis

Chicken meat and eggs are important sources of food for the world population. The significant increase in food demand has pushed the food industry toward a rapid non-expensive production which in turn raises ethical issues. How chicken are cultivated and processed in food industry is no longer acceptable. Ethical and economical concerns emerging from chicken culling need to be solved in the near future. Indeed, in egg production industry, male chicken are killed at the age of 1-day post-hatching since they are not egg producers. A number of laboratory all over the world are looking for innovative non-invasive sexing methods to determine the sex of chicken in the early stages of the development before hatching. It will allow males' chicken elimination before the pain-feeling stages. In order to evaluate the efficiency of these methods, the scientific community need a reliable, easy to use and cost-effective in-ovo invasive sexing method. In this report, we developed two new invasive assays based on PCR and Q-PCR techniques respectively, which fulfil the above mentioned requirements. In the same line with other groups, we exploited the differences betweed males (ZZ) and females (ZW) chicken sexual chromosomes. We identified two genes, SWIM and Xho-I, on chromosome W and DMRT gene on chromosome Z allowing a clear discrimination between the two sexes using PCR and qPCR respectively. These two new genomic markers and their corresponding methods not only increase the accuracy but also reduce time and cost of the test compared to previously developed sexing methods. Depending on the technology available in the lab, one can choose between the two techniques requiring different machines and expertise.

A new marker based on the avian spindlin gene that is able to sex most birds, including species problematic to sex with CHD markers

We have developed a new marker (Z43B) that can be successfully used to identify the sex of most birds (69%), including species difficult or impossible to sex with other markers. We utilized the zebra finch Taeniopygia guttata EST microsatellite sequence (CK309496) which displays sequence homology to the 5' untranslated region (UTR) of the avian spindlin gene. This gene is known to be present on the Z and W chromosomes. To maximize cross-species utility, the primer set was designed from a consensus sequence created from homologs of CK309496 that were isolated from multiple distantly related species. Both the forward and reverse primer sequences were 100% identical to 14 avian species, including the Z chromosome of eight species and the chicken Gallus gallus W chromosome, as well as the saltwater crocodile Crocodylus porosus. The Z43B primer set was assessed by genotyping individuals of known sex belonging to 61 non-ratite species and a single ratite. The Z and W amplicons differed in size making it possible to distinguish between males (ZZ) and females (ZW) for the majority (69%) of non-ratite species tested, comprising 10 orders of birds. We predict that this marker will be useful for obtaining sex-typing data for ca 6,869 species of birds (69% of non-ratites but not galliforms). A wide range of species could be sex-typed including passerines, shorebirds, eagles, falcons, bee-eaters, cranes, shags, parrots, penguins, ducks, and a ratite species, the brown kiwi, Apteryx australis. Those species sexed include species impossible or problematic to sex-type with other markers (magpie, albatross, petrel, eagle, falcon, crane, and penguin species). Zoo Biol. 35:533-545, 2016. © 2016 The Authors. Zoo Biology published by Wiley Periodicals, Inc.

The Tudor domain protein Spindlin1 is involved in intrinsic antiviral defense against incoming hepatitis B Virus and herpes simplex virus type 1

Hepatitis B virus infection (HBV) is a major risk factor for the development of hepatocellular carcinoma. HBV replicates from a covalently closed circular DNA (cccDNA) that remains as an episome within the nucleus of infected cells and serves as a template for the transcription of HBV RNAs. The regulatory protein HBx has been shown to be essential for cccDNA transcription in the context of infection. Here we identified Spindlin1, a cellular Tudor-domain protein, as an HBx interacting partner. We further demonstrated that Spindlin1 is recruited to the cccDNA and inhibits its transcription in the context of infection. Spindlin1 knockdown induced an increase in HBV transcription and in histone H4K4 trimethylation at the cccDNA, suggesting that Spindlin1 impacts on epigenetic regulation. Spindlin1-induced transcriptional inhibition was greater for the HBV virus deficient for the expression of HBx than for the HBV WT virus, suggesting that HBx counteracts Spindlin1 repression. Importantly, we showed that the repressive role of Spindlin1 is not limited to HBV transcription but also extends to other DNA virus that replicate within the nucleus such as Herpes Simplex Virus type 1 (HSV-1). Taken together our results identify Spindlin1 as a critical component of the intrinsic antiviral defense and shed new light on the function of HBx in HBV infection.

Identification of avian W-linked contigs by short-read sequencing

Background

The female-specific W chromosomes and male-specific Y chromosomes have proven difficult to assemble with whole-genome shotgun methods, creating a demand for new approaches to identify sequence contigs specific to these sex chromosomes. Here, we develop and apply a novel method for identifying sequences that are W-specific.

Results

Using the Illumina Genome Analyzer, we generated sequence reads from a male domestic chicken (ZZ) and mapped them to the existing female (ZW) genome sequence. This method allowed us to identify segments of the female genome that are underrepresented in the male genome and are therefore likely to be female specific. We developed a Bayesian classifier to automate the calling of W-linked contigs and successfully identified more than 60 novel W-specific sequences.

Conclusions

Our classifier can be applied to improve heterogametic whole-genome shotgun assemblies of the W or Y chromosome of any organism. This study greatly improves our knowledge of the W chromosome and will enhance future studies of avian sex determination and sex chromosome evolution.

Dynamic distribution of spindlin in nucleoli, nucleoplasm and spindle from primary oocytes to mature eggs and its critical function for oocyte-to-embryo transition in gibel carp

Spindlin (Spin) was thought as a maternal-effect factor associated with meiotic spindle. Its role for the oocyte-to-embryo transition was suggested in mouse, but its direct evidence for the function had been not obtained in other vertebrates. In this study, we used the CagSpin-specific antibody to investigate CagSpin expression pattern and distribution during oogenesis of gibel carp (Carassius auratus gibelio). First, the oocyte-specific expression pattern and dynamic distribution was revealed in nucleoli, nucleoplasm, and spindle from primary oocytes to mature eggs by immunofluorescence localization. In primary oocytes and growth stage oocytes, CagSpin accumulates in nucleoli in increasing numbers along with the oocyte growth, and its disassembly occurs in vitellogenic oocytes, which implicates that CagSpin may be a major component of a large number of nucleoli in fish growth oocytes. Then, co-localization of CagSpin and β-tubulin was revealed in meiotic spindle of mature egg, indicating that CagSpin is one spindle-associated factor. Moreover, microinjection of CagSpin-specific antibody into the fertilized eggs blocked the first cleavage, and found that the CagSpin depletion resulted in spindle assembly disturbance. Thereby, our study provided the first direct evidence for the critical oocyte-to-embryo transition function of Spin in vertebrates, and confirmed that Spin is one important maternal-effect factor that participates in oocyte growth, oocyte maturation, and oocyte-to-embryo transition.

Molecular cloning and characterization of the germline-restricted chromosome sequence in the zebra finch

The zebra finch (Taeniopygia guttata) germline-restricted chromosome (GRC) is the largest chromosome and has a unique system of transmission in germ cells. In the male, the GRC exists as a single heterochromatic chromosome in the germline and is eliminated from nuclei in late spermatogenesis. In the female, the GRC is bivalent and euchromatic and experiences recombination. These characteristics suggest a female-specific or female-beneficial function of the GRC. To shed light on the function of GRC, we cloned a portion of the GRC using random amplified polymorphic DNA-polymerase chain reaction and analyzed it using molecular genetic and cytogenetic methods. The GRC clone hybridized strongly to testis but not blood DNA in genomic Southern blots. In fluorescent in situ hybridization analysis on meiotic chromosomes from synaptonemal complex spreads, the probe showed hybridization across a large area of the GRC, suggesting that it contains repetitive sequences. We isolated a sequence homologous to the GRC from zebra finch chromosome 3 and a region of chicken chromosome 1 that is homologous to zebra finch chromosome 3; the phylogenetic analysis of these three sequences suggested that the GRC sequence and the zebra finch chromosome 3 sequence are most closely related. Thus, the GRC sequences likely originated from autosomal DNA and have evolved after the galliform-passeriform split. The present study provides a foundation for further study of the intriguing GRC.

Disruption of FEM1C-W gene in zebra finch: evolutionary insights on avian ZW genes

Sex chromosome genes control sex determination and differentiation, but the mechanisms of sex determination in birds are unknown. In this study, we analyzed the gene FEM1C which is highly conserved from Caenorhabditis elegans to higher vertebrates and interacts with the sex determining pathway in C. elegans. We found that FEM1C is located on the Z and W chromosome of zebra finches and probably other Passerine birds, but shows only Z linkage in other avian orders. In the zebra finch, FEM1C-W is degraded because of a point mutation and possibly because of loss of the first exon containing the start methionine. Thus, FEM1C-W appears to have degenerated or been lost from most bird species. FEM1C-Z is expressed in a cytoplasmic location in zebra finch fibroblast cells, as in C. elegans. FEM1C represents an interesting example of evolutionary degradation of a W chromosome gene.

Characterization of Spindlin1 isoform2 in mouse testis

AIM

To investigate the expression of Spindlin 1 (Spin 1) isoform2 and assess its function in mouse testis.

METHODS

First, reverse-transcription polymerase chain reaction (RT-PCR) was used to determine whether Spin1 isoform2 is present in mouse testis. Then the expression patterns of the isoform between newborn and adult mice testes were compared by immunoblot analysis. Finally, the diversity of its localization in mice testes at different ages (days 0, 7, 14, 21, 28 and 60) was observed by immunohistochemistry. The localization of the protein in mouse sperm was also investigated by immunofluorescence.

RESULTS

The RT-PCR results show that Spin1 isoform2 is present in mouse testis. As shown by immunoblot analysis, the isoform was more highly expressed in adult testes compared with newborn testes. Interestingly, Spin1 isoform2 did not show up in the cytoplasm of primary spermatocytes until day 14. Also, the protein exists at the tail of the mouse sperm.

CONCLUSION

Spin1 isoform2 is a protein expressed highly in adult testis, which might be involved in spermatogenesis and could be necessary for normal sperm motility.

Overexpression of spindlin1 induces metaphase arrest and chromosomal instability

Spin/Ssty gene family is high conserved and very abundant transcript involved in gametogenesis, which was repeatedly detected in early embryo. Nevertheless, the biologic roles of the members are still largely unknown. Previously we have identified human gene spindlin1 as a homologue of the family from ovarian cancer cells, and reported that stable overexpression of spindlin1 could transform NIH3T3 cells and induce tumorigenesis in nude mouse. Here, we showed that spindlin1, as a nuclear protein, was relocated during mitosis. A fraction of spindlin1 proteins was dynamic distributed along mitotic spindle tubulin and enriched at midzone following anaphase entering. We also showed that transient overexpression of spindlin1 induced cell cycle delay in metaphase, caused mitotic spindle defects, and resulted in chromosome instability, micronucleus and multinuclear giant cells formation. Moreover, time-lapse microscopy revealed that these cells arrested at metaphase for more than 3 h with chromosome nondisjunction or missegregation. Furthermore, Mad2 up-regulation in these cells suggested that overexpression of spindlin1 may affect the bipolar spindle correctly attachment to chromosomes and activate spindle checkpoint. Taken together, these data demonstrated that excess spindlin1 protein may be detrimental for spindle microtubule organization, chromosomal stability and can potentially contribute to the development of cancer.

Chromosomal mapping of chicken mega-telomere arrays to GGA9, 16, 28 and W using a cytogenomic approach

Four mega-telomere loci were mapped to chicken chromosomes 9, 16, 28, and the W sex chromosome by dual-color fluorescence in situ hybridization using a telomeric sequence probe and BAC clones previously assigned to chicken chromosomes. The in-common features of the mega-telomere chromosomes are that microchromosomes are involved rather than macrochromosomes; in three cases (9, 16, 28) acrocentrics are involved with the mega-telomeres mapping to the p arms. Three of the four chromosomes (9, 16, W) encode tandem repeats which in two cases (9 and 16) involve the ribosomal DNA arrays (the 5S and 18S-5.8S-28S gene repeats, respectively). All involved chromosomes have a typical-sized telomere on the opposite terminus. Intra- and interindividual variation for mega-telomere distribution are discussed in terms of karyotype abnormalities and the potential for mitotic instability of some telomeres. The diversity and distribution of telomere array quantity in the chicken genome should be useful in contributing to research related to telomere length regulation - how and by what mechanism genomes and individual chromosomes establish and maintain distinct sets of telomere array sizes, as well as for future studies related to stability of the chicken genome affecting development, growth, cellular lifespan and disease. An additional impact of this study includes the listing of BAC clones (26 autosomal and six W BACs tested) that were cytogenetically verified; this set of BACs provide a useful tool for future cytogenetic analyses of the microchromosomes.

Sequence analysis of full-length cDNA of sex chromosome-linked novel gene 2d-2F9 in Gallus gallus

We obtained two novel W chromosome-linked chick genes by the use of female-male subtraction macroarrays, one of which, 2d-2F9, (recorded as AB188527 in DDBJ) did not have sufficient length (776 bp) to reveal its real form or characteristics. Hence, we obtained full-length Z-linked and W-linked 2d-2F9 genes of 2596 bp and 2589 bp respectively by the oligo-capping and RACE methods. Sequence analysis of these genes not only revealed that there is a counterpart of the W-linked 2d-2F9 gene on the Z chromosome, but also that there is a low homologous area at 5'-UTR between the W- and Z-kinked genes. Using this information, we designed a set of primers to identify sex and to select clones having the Z and W-linked gene (named 2d-2F9-Z and 2d-2F9-W), and also prepared two sets of primers for RT-PCR. These genes were found to be expressed constitutively and ubiquitously from the early embryo to the hatched chick, and they were assigned to the AAA ATP-superfamily.

Comparison of the chicken and zebra finch Z chromosomes shows evolutionary rearrangements

Using fluorescent in-situ hybridization (FISH) of zebra finch (Taeniopygia guttata) bacterial artificial chromosome (BAC) clones, we determined the chromosomal localizations of 14 zebra finch genes that are Z-linked in chickens: ATP5A1, CHD1, NR2F1, DMRT1, PAM, GHR, HSD17B4, NIPBL, ACO1, HINT1, SMAD2, SPIN, NTRK2 and UBE2R2. All 14 genes also map to the zebra finch Z chromosome, indicating substantial conservation of gene content on the Z chromosome in the two avian lineages. However, the physical order of these genes on the zebra finch Z chromosome differed from that of the chicken, in a pattern that would have required several inversions since the two lineages diverged. Eight of 14 zebra finch BAC DNA showed cross-hybridization to the W chromosome, usually to the entire W chromosome, suggesting that repetitive sequences are shared by the W and Z chromosomes. These repetitive sequences likely evolved in the finch lineage after it diverged from the Galliform lineage.

FISH on avian lampbrush chromosomes produces higher resolution gene mapping

Giant lampbrush chromosomes, which are characteristic of the diplotene stage of prophase I during avian oogenesis, represent a very promising system for precise physical gene mapping. We applied 35 chicken BAC and 4 PAC clones to both mitotic metaphase chromosomes and meiotic lampbrush chromosomes of chicken (Gallus gallus domesticus) and Japanese quail (Coturnix coturnix japonica). Fluorescence in situ hybridization (FISH) mapping on lampbrush chromosomes allowed us to distinguish closely located probes and revealed gene order more precisely. Our data extended the data earlier obtained using FISH to chicken and quail metaphase chromosomes 1-6 and Z. Extremely low levels of inter- and intra-chromosomal rearrangements in the chicken and Japanese quail were demonstrated again. Moreover, we did not confirm the presence of a pericentric inversion in Japanese quail chromosome 4 as compared to chicken chromosome 4. Twelve BAC clones specific for chicken chromosome 4p and 4q showed the same order in quail as in chicken when FISH was performed on lampbrush chromosomes. The centromeres of chicken and quail chromosomes 4 seem to have formed independently after centric fusion of ancestral chromosome 4 and a microchromosome.

Gene Expression Profiling of Ovarian Tissues for Determination of Molecular Pathways Reflective of Tumorigenesis

Ovarian cancer is the fourth leading cause of gynecological cancer death among women in the United States. Early detection is a critical prerequisite to initiating effective cancer therapy. Gene microarray technology and proteomics have provided much of the biomarkers with potential use for diagnosis. However, more research is needed to fully understand disease onset and progression. To this end, we have performed microarray analysis with the goal of identifying molecular interaction networks defining tumor growth. Microarray analysis was performed on a limited set of ovarian tissues with various pathological diagnoses using Human Genome Focus Array (HGFA) for the detection of approximately 8500 human transcripts. Hierarchical clustering identified groups of ovarian tissues reflective of low malignant potential/early cancer onset and possible pre-cancerous stages involving small molecule, cytokine and/or hormone-dependent feed-back responses specific to the pelvic reproductive system and a priori initiated tumor suppression mechanisms. ANOVA followed by post hoc Scheffe confirmed our hypotheses. Moreover, we established a protein/protein interaction database associated with HGFA probe sets. This database was used to build and visualize molecular networks integrating small but significant changes in gene expression. In conclusion, we were able for the first time to delineate an intersecting genetic pattern linking ovarian tissues reflective of low potential malignancy/early cancer onset stages via long distance signaling between tissues of gynecological origin.

Sex-dependent gene expression in early brain development of chicken embryos

BACKGROUND

Differentiation of the brain during development leads to sexually dimorphic adult reproductive behavior and other neural sex dimorphisms. Genetic mechanisms independent of steroid hormones produced by the gonads have recently been suggested to partly explain these dimorphisms.

RESULTS

Using cDNA microarrays and real-time PCR we found gene expression differences between the male and female embryonic brain (or whole head) that may be independent of morphological differentiation of the gonads. Genes located on the sex chromosomes (ZZ in males and ZW in females) were common among the differentially expressed genes, several of which (WPKCI-8, HINT, MHM non-coding RNA) have previously been implicated in avian sex determination. A majority of the identified genes were more highly expressed in males. Three of these genes (CDK7, CCNH and BTF2-P44) encode subunits of the transcription factor IIH complex, indicating a role for this complex in neuronal differentiation.

CONCLUSION

In conclusion, this study provides novel insights into sexually dimorphic gene expression in the embryonic chicken brain and its possible involvement in sex differentiation of the nervous system in birds.

The evolution of the spindlin gene in birds: sequence analysis of an intron of the spindlin W and Z gene reveals four major divisions of the Psittaciformes

The Psittaciformes (parrots, parakeets) are among the most widely held captive birds. Yet, their evolution and their phylogenetic relationships have been relatively little studied. This paper describes the phylogenetic relationships between a number of Psittaciformes as derived from the sequences of the third intron of the Z-chromosomal and W-chromosomal spindlin genes. The Z-chromosomal sequences of the kakapo (Strigops habroptilus), the kea (Nestor notabilis), and the kaka (Nestor meridionalis) from New Zealand form a cluster which is the sister group to all other Psittaciformes. The results show further that the Z-chromosomal sequences of the other species can be divided into two groups based on the occurrence of a sequence element ACCCT. The group with the insert (A) is mainly from species with an Australasian geographical distribution and includes such species as the Lories (Lorius, etc.), the budgerigar (Melospittacus undulatus), and the rosellas (Platycercus). It also includes the African lovebirds (Agapornidae), which are the only representative of group A outside Australasia. Group B, without the insert, includes the neotropical parrots and parakeets such as the amazons (Amazona, etc.), the macaws (Ara, etc.), and the conures (Aratinga, etc.), the Australian Cacatuini and the African species such as the African grey parrot (Psittacus erithacus) as well as Coracopsis vasa from Madagascar and Psittrichas fulgidus from New Guinea. The W-chromosomal sequence data show that another division of the Psittacidae is found in the replacement of a pyrimidine-rich segment occurring in many non-psittacines as well as the kakapo (S. habroptilus), the kea (N. notabilis), the kaka (N. meridionalis), and the Cacatuini by a microsatellite consisting of a variable number of TATTA monomers in the other Psittaciformes. The results support a Gondwanan origin of the Psittaciformes and the suggestion that paleogeographic events were a major force in psittacine divergence.

Fast accumulation of nonsynonymous mutations on the female-specific W chromosome in birds

Following cessation of recombination during sex chromosome evolution, the nonrecombining sex chromosome is affected by a number of degenerative forces, possibly resulting in the fixation of deleterious mutations. This might take place because of weak selection against recessive or partly recessive deleterious mutations due to permanent heterozygosity of nonrecombining chromosomes. Furthermore, population genetic processes, such as selective sweeps, background selection, and Muller's ratchet, result in a reduction in Ne, which increase the likelihood of fixation of deleterious mutations. Theory thus predicts that nonrecombining genes should show increased levels of nonsynonymous (dN) to synonymous substitutions (dS). We tested this in an avian system by estimating the ratio between dN and dS in six gametologous gene pairs located on the Z chromosome and the nonrecombining, female-specific W chromosome. In comparisons, we found a significantly higher dN/dS ratio for the W-linked than the Z-linked copy in three of the investigated genes. In a concatenated alignment of all six genes, the dN/dS ratio was six times higher for W-linked than Z-linked genes. By using human and mouse as outgroup in maximum likelihood analyses, W-linked genes were found to evolve differently compared with their Z-linked gametologues and outgroup sequences. This seems not to be a consequence of functional diversification because d(N)/d(S) ratios between gametologous gene copies were consistently low. We conclude that deleterious mutations are accumulating at a high rate on the avian W chromosome, probably as a result of the lack of recombination in this female-specific chromosome.

Spindlin1, a novel nuclear protein with a role in the transformation of NIH3T3 cells

spindlin1, a novel human gene recently isolated by our laboratory, is highly homologous to mouse spindlin gene. In this study, we cloned cDNA full-length of this novel gene and send it to GenBank database as spindlin1 (Homo sapiens spindlin1) with Accession No. AF317228. In order to investigate the function of spindlin1, we studied further the subcellular localization of Spindlin1 protein and the effects of spindlin1 overexpression in NIH3T3 cells. The results showed that the fusion protein pEGFP-N1-spindlin1 was located in the nucleus and the C-terminal is correlated with nuclear localization of Spindlin1 protein. NIH3T3 cells which could stably express spindlin1 as a result of RT-PCR analysis compared with the control cells displayed a complete morphological change; made cell growth faster; and increased the percentage of cells in G2/M and S phase. Furthermore, overexpressed spindlin1 cells formed colonies in soft agar in vitro and formed tumors in nude mice. Our findings provide direct evidence that spindlin1 gene may contribute to tumorigenesis.

Meiotic instability of chicken ultra-long telomeres and mapping of a 2.8 megabase array to the W-sex chromosome

The objective of this research was to study the meiotic stability of a subset of chicken telomere arrays, which are the largest reported for any vertebrate species. Inheritance of these ultra-long telomere arrays (200 kb to 3 mb) was studied in a highly homozygous inbred line, UCD 003 (F >or= 99.9). Analysis of array transmission in four families indicated unexpected heterogeneity and non-Mendelian segregation including high-frequency-generation of novel arrays. Additionally, the largest array detected (2.8 Mb) was female-specific and correlated to the most intense telomeric DNA signal on the W-sex chromosome by fluorescence in situ hybridization (FISH). These results are discussed in regard to the potential functions of the ultra-long telomere arrays in the chicken genome including generation of genetic variation through enhanced recombination, protection against erosion by providing a buffer for gene-dense regions, and sex-chromosome organization.

Chromosomal polymorphism and comparative painting analysis in the zebra finch

The zebra finch (Taeniopygia guttata) is often studied because of its interesting behaviour and neurobiology. Genetic information on this species has been lacking, making analysis of informative mutants difficult. Here we report on an improved cytological method for preparation of metaphase chromosomes suitable for fluorescent in situ hybridization of adult birds. We found that individual chicken chromosome paints usually hybridized to single zebra finch chromosomes, indicating only minor chromosomal rearrangements since the evolutionary divergence of these two species, and suggesting that the genomic location of chicken genes will predict the location of zebra finch orthologues. Chicken chromosome 1 appears to have split into two macrochromosomes in zebra finches, and chicken chromosome 4 paint hybridizes to a zebra finch macrochromosome and a microchromosome. This pattern was confirmed by mapping the androgen receptor (AR), which is located on chicken chromosome 4 but on a zebra finch microchromosome. We detected a telocentric/submetacentric polymorphism of chromosome 6 in our colony of zebra finches, and found that the polymorphism was inherited in a Mendelian pattern.

Identification of three duplicated Spin genes in medaka (Oryzias latipes)

Gene and genomic duplications are very important and frequent events in fish evolution, and the divergence of duplicated genes in sequences and functions is a focus of research on gene evolution. Here, we report the identification and characterization of three duplicated Spindlin (Spin) genes from medaka (Oryzias latipes): OlSpinA, OlSpinB, and OlSpinC. Molecular cloning, genomic DNA Blast analysis and phylogenetic relationship analysis demonstrated that the three duplicated OlSpin genes should belong to gene duplication. Furthermore, Western blot analysis revealed significant expression differences of the three OlSpins among different tissues and during embryogenesis in medaka, and suggested that sequence and functional divergence might have occurred in evolution among them.

Identification of a Spindlin homolog in gibel carp (Carassius auratus gibelio)

Spindlin has been suggested to play an important role during the transition from oocyte maturation to embryo development in mouse, but its homolog similar to the mouse Spindlin in molecular and expression characterization has not been identified up to now in other vertebrates. In this study, a full length of cDNA sequence is cloned and sequenced from the gibel carp (Carassius auratus gibelio). It contains 1240 nucleotides with an open reading frame of 771 nt encoding 257 amino acids. Based on its amino acid sequence alignment and comparison analysis with the known Spin family proteins, the newly cloned Spin is named Carassius auratus gibelio Spindlin (CagSpin). Its product could be detected from mature eggs to blastula embryos, but its content decreased from the two-cell stage, and could not be detected after the gastrula stage. It suggests that the CagSpin should be a maternal protein that is expressed during oocyte maturation, and plays a crucial role in early cleavage of embryogenesis. CagSpin is the first homolog similar to mouse spindlin identified in fish, and also in other vertebrates. GST pull-down assay reveals the first biochemical evidence for the association of CagSpin and beta-tubulin, the microtubule component. Therefore, CagSpin may play important functions by interacting with beta-tubulin and other spindle proteins during oocyte maturation and egg fertilization.

Evolutionary strata on the chicken Z chromosome: implications for sex chromosome evolution

The human X chromosome exhibits four "evolutionary strata," interpreted to represent distinct steps in the process whereby recombination became arrested between the proto X and proto Y. To test if this is a general feature of sex chromosome evolution, we studied the Z-W sex chromosomes of birds, which have female rather than male heterogamety and evolved from a different autosome pair than the mammalian X and Y. Here we analyze all five known gametologous Z-W gene pairs to investigate the "strata" hypothesis in birds. Comparisons of the rates of synonymous substitution and intronic divergence between Z and W gametologs reveal the presence of at least two evolutionary strata spread over the p and q arms of the chicken Z chromosome. A phylogenetic analysis of intronic sequence data from different avian lineages indicates that Z-W recombination ceased in the oldest stratum (on Zq; CHD1Z, HINTZ, and SPINZ) 102-170 million years ago (MYA), before the split of the Neoaves and Eoaves. However, recombination continued in the second stratum (on Zp; UBAP2Z and ATP5A1Z) until after the divergence of extant avian orders, with Z and W diverging 58-85 MYA. Our data suggest that progressive and stepwise cessation of recombination is a general feature behind sex chromosome evolution.

Sexual differentiation of the zebra finch song system

The song system of zebra finches (Taeniopygia gutatta) is highly sexually dimorphic. Only males sing, and the brain regions and muscles controlling song are much larger in males than in females. Development of the song system is highly sensitive to steroid hormones. However, unlike similar sexually dimorphic systems in other animal models, masculinization of song system structure and function is most likely not induced by testosterone secreted from the testes. Instead, sex-specific development of the neural song system appears to be regulated by factors intrinsic to the brain, probably by the expression of sex chromosome gene(s) that influence the levels of estradiol synthesized in the brain and/or the responses of brain tissue to estradiol. However, the existing data are complex and in some cases contradictory. More work is required to identify the critical genes and their relationships with steroid hormones.

Comparative mapping of Z-orthologous genes in vertebrates: implications for the evolution of avian sex chromosomes

Sex chromosomes of birds and mammals are highly differentiated and share several cytological features. However, comparative gene mapping reveals extensive conserved synteny between the chicken Z sex chromosome and human chromosome 9 but not the human X sex chromosome, implying an independent origin of avian and mammalian sex chromosomes. To better understand the evolution of the avian Z chromosome we analysed the synteny of chicken Z-linked genes in zebrafish, which is the best-mapped teleost genome so far. Existing zebrafish maps do not support the existence of an ancestral Z linkage group in the zebrafish genome, whereas mammalian X-linked genes show at least some degree of synteny conservation. This is consistent with in situ hybridisation mapping data in the freshwater pufferfish, Tetraodon nigroviridis where mammalian X-linked genes show a much higher degree of conserved synteny than human chromosome 9 or the avian Z chromosome. Collectively, these data argue in favour of a more recent evolution of the avian Z chromosome, compared with the mammalian X.

Sex and death in birds: a model of dosage compensation that predicts lethality of sex chromosome aneuploids

Birds show female heterogamety, with ZZ males and ZW females. It is still not clear whether the W is female-determining, or whether two doses of the Z chromosomes are male-determining, or both. This question could easily be settled by the sexual phenotypes of ZZW and ZO birds, in the same way that the sexual phenotypes of XXY and XO showed that the Y is male determining in humans, but that the dosage of an X-borne gene determines sex in Drosophila. However, despite extensive searches, no ZZW or ZO diploid birds have been satisfactorily documented, so we must assume that these genotypes are embryonic lethals. Given that ZW and ZZ are viable and the W contains few genes it is not clear why this should be so. Here I propose that sex chromosome aneuploids are lethal in chicken because, to achieve dosage compensation, a locus on the W chromosome controls the upregulation of genes on the Z in ZW females. ZO birds would therefore have only half the normal dose of Z-linked gene product and ZZW would have twice the amount, both of which would undoubtedly be incompatible with life. Reports of other aneuploids and triploids are also consistent with this hypothesis.

Molecular and cytological characterization of SspI-family repetitive sequence on the chicken W chromosome

A genomic clone, pWS44, isolated from the chicken W chromosome-specific genomic library contained a partial (226-bp) sequence of a novel SspI-family repetitive sequence. A genomic clone, pWPRS09, containing a 508-bp SspI fragment (a repeating unit of the family) was subsequently obtained and sequenced. This 0.5-kb unit is tandemly repeated about 11,300 times. FISH to mitotic and lampbrush W chromosomes indicates that the SspI-family is located on the chromomere 6 between heterochromatic and distal non-heterochromatic regions on the short arm. The SspI-family sequence was proved to be a good positional marker in FISH mapping of active genes in the non-heterochromatic region on the lampbrush W chromosome. The presence of SspI-family repetitive sequence is limited to the genus Gallus (chickens and jungle fowls). The 0.5-kb repeating unit contains a 120-bp stretch of polypurine/polypyrimidine sequence (GGAGA repeats), shows no DNA curvature, and rapid electrophoretic mobility in 4% polyacrylamide gel at 4 degrees C. The SspI-family forms a relatively diffused chromatin structure in nuclei. These features are distinctly different from those of XhoI- and EcoRI-family sequences on the W chromosome. The total amount of non-repetitive DNA in the chicken W chromosome is estimated to be about 10 Mb.

Sex identification by alternative polymerase chain reaction methods in falconiformes

A number of avian species are difficult to sex morphologically, especially as nestlings. Like other avian species, many species of Falconiformes are sexually monomorphic. Therefore, it is desirable that new methods based on DNA analysis are established in Falconiformes and other sexual monomorphic species. We identified sex in Falconiformes by two alternative methods. First, we used a sexing method based on the intronic length variation between CHD1W and CHD1Z using primers flanking the intron. In this method, two species of Falconidae could be identified for sexing. However, six species of Accipitridae could not, because they have few length variations. The second method used was based on differences in sequences between CHD1W and CHD1Z. From sequence analysis, a 3'-terminal mismatch primer on point mutation conserved among Falconiformes was designed, and identification of sex with the amplification refractory mutation system (ARMS) was performed. This method could identify sex in all species tested. In addition, because the 3'-terminal mismatch primer was designed on a point mutation conserved among Falconiformes, ARMS with these primers may identify sex in all Falconiformes. These are simple and rapid sexing methods, since only polymerase chain reaction (PCR) and agarose electrophoresis are required. In conclusion, sex identification by an alternative PCR approach based on intronic length variation and on differences in sequences between CHD1W and CHD1Z proved applicable to and useful for Falconiformes.

FET-1: a novel W-linked, female specific gene up-regulated in the embryonic chicken ovary

A differential expression screen for sex-determining genes in the embryonic chicken gonad revealed a novel gene called Female Expressed Transcript 1 (FET-1). Fluorescent in situ hybridization analysis mapped FET-1 to the female specific W chromosome. Whole mount in situ hybridization showed that FET-1 expression was restricted to females and up-regulated in the cortex of the left gonad during the sex-determining period. Female specific expression was also observed in the embryonic caudal somites, neural tube and waste collection ducts.

Functional cloning of SPIN-2, a nuclear anti-apoptotic protein with roles in cell cycle progression

The balance between hematopoietic cell viability and apoptosis is regulated by exogenous growth factors, however, the molecular mechanisms by which these trophic factors exert their effects remain obscure. A functional retroviral cDNA library-based screen was employed to identify genes that prevent growth factor withdrawal-mediated apoptosis in the myeloid progenitor cell 32Dcl3. This approach identified three classes of genes: those with known roles in apoptosis (bcl-X(L) and ornithine decarboxylase); genes previously identified but not linked directly to apoptotic signaling (O-linked N-acetylglucosamine transferase); and a previously uncharacterized gene we termed SPIN-2. In 32Dcl3 cells, expression of exogenous SPIN-2 provides 25% protection from apoptosis following growth factor withdrawal compared to controls which show approximately 1-2% survival. SPIN-2 overexpression slows cell growth rates and increases the percentage of cells in G(2)/M (32% vs control cells at 12%). Immunolocalization studies indicate that myc-epitope tagged SPIN-2 proteins, which retain their anti-apoptotic function, reside in the nucleus, whereas a C-terminal deletion mutant that loses its anti-apoptotic activity is located in the cytoplasm. These studies suggest that SPIN-2 is a novel nuclear protein that functions to regulate cell cycle progression and this activity is related to the inhibition of apoptosis following the removal of essential growth factors.

The Spin/Ssty repeat: a new motif identified in proteins involved in vertebrate development from gamete to embryo

BACKGROUND

The homologous genes Spin (spindlin) and Ssty were first identified as genes involved in gametogenesis and seem to occur in multiple copies in vertebrate genomes. The mouse spindlin (Spin) protein was reported to interact with the spindle apparatus during oogenesis and to be a target for cell-cycle-dependent phosphorylation. The transcript of the mouse Ssty gene is specific to sperm cells. In the chicken, spindlin was found to co-localize with SUMO-1 to nuclear dots during interphase in fibroblasts, but to co-localize with chromosomes during mitosis. Thus, Spin/Ssty genes might be important in the transition from sperm cells and oocytes to the early embryo, as well as in mitosis.

RESULTS

Here we report the discovery of a new protein motif of around 50 amino acids in length, the Spin/Ssty repeat, in proteins of the Spin/Ssty (spindlin) family. We found that in one member of this family, the human SPIN gene, each repeat resides in its own exon, supporting our view that Spin/Ssty repeats are independent functional units. On the basis of different secondary-structure prediction methods, we propose a four-stranded beta-structure for the Spin/Ssty repeat.

CONCLUSIONS

The discovery of the Spin/Ssty repeat might contribute to the further elucidation of the structure and function of spindlin-family proteins. We predict that the tertiary structure of spindlin-like proteins is composed of three modules of Spin/Ssty repeats.

Dosage compensation: do birds do it as well?

In birds males carry ZZ and females ZW sex chromosomes, and it has been proposed that there is no dosage compensation in the expression of sex-linked genes. However, recent data suggest the opposite, indicating that male and female birds might demonstrate similar levels of expression of Z-linked genes. If they do, the equalization between the sexes is probably not achieved by inactivation of one of the male Z chromosomes. Other possible mechanisms include the transcription of Z-linked genes being upregulated in females or downregulated in males, or equalization at the translation stage in either sex. A recently identified hypermethylated region on the Z chromosome, with similarities to the X inactivation centre on the mammalian X chromosome, might play a part in this process or have a role in avian sex determination.