Search Results (24)

Background/Objectives: The domestic yak (Bos grunniens) is a livestock species of major relevance in high-altitude environments and an important model for studying adaptation and reproductive isolation within Bovini. Despite its close phylogenetic relationship with cattle (Bos taurus), yak × cattle hybrids show a marked sex-biased fertility pattern, with fertile females and generally sterile F1 males, suggesting that subtle chromosomal or genomic differences may underlie post-zygotic reproductive barriers. In this study, we performed a cytogenetic characterization of eight adult yak bulls imported and reared in Central Italy using conventional and molecular cytogenetic approaches. Results: GTG-, RBG-, RBA- and CBA-banding confirmed the yak diploid number as 2n = 60 and the fundamental number as NF = 62, with banding patterns highly comparable to the standardized cattle karyotype. CBA-banding showed an X chromosome lacking evident constitutive heterochromatin and a Y chromosome with distal C-positive blocks. Chromosome instability was low, with 3.75% abnormal metaphases, mainly represented by chromatid and iso-chromatid breaks, while the mean sister chromatid exchange (SCE) rate was 5.19 ± 2.14 per cell. Sequential Ag-NOR/RBA staining localized nucleolar organizer regions (NORs) at the telomeres of autosomes 2, 3, 4, 11 and 25, as in cattle. Zoo-FISH using bovine chromosome paints for X, Y, 5 and 15 showed complete hybridization to the corresponding yak chromosomes, and BAC-FISH mapped the Y-linked ZFY and SRY genes to positions homologous to those reported in cattle. A comparative bioinformatics analysis of available yak genome assemblies confirmed the overall genome-wide correspondence with cattle, while revealing chromosome orientation issues and small local inconsistencies that may be relevant for comparative mapping and probe design. Conclusions: Overall, at the resolution tested, these findings support broad macrostructural conservation of yak and cattle karyotypes and provide cytogenetic reference data for yak populations reared outside of their traditional range. The persistence of F1 male sterility despite this large-scale chromosomal conservation suggests that fine-scale sex chromosome differences, particularly involving pseudoautosomal regions, recombination boundaries, or heterochromatin organization, may deserve targeted investigation. Full article

Background/Objectives: The Y chromosome plays a crucial role in male fertility, sex determination, and spermatogenesis, yet it remains poorly characterized in Mediterranean river buffalo (Bubalus bubalis, 2n = 50) because of its high repeat content, extensive heterochromatin, and complex palindromic structures. Although a chromosome-level Y assembly is available for swamp buffalo (2n = 48), no equivalent reference exists for the river type. Methods: To address this gap, Y chromosomes from 10 Mediterranean buffalo bulls were isolated by laser microdissection following peripheral blood culture and whole-chromosome amplification. Probe specificity was verified by FISH, and amplified Y chromosomes were sequenced using Illumina NovaSeq 6000 (Illumina, San Diego, CA, USA). Sequencing data were assembled and analysed through de novo assembly, repeat identification, sequence alignment, and variant detection. Comparative analyses included alignment to the swamp buffalo Y chromosome and annotation of Y-linked genes using the Bos taurus reference genome. Results: FISH confirmed the specificity of the isolated material, showing strong signals on the Y chromosome and on X/Y PAR and heterochromatic regions. Sequencing generated over 240 million paired-end reads, and de novo assembly produced 566,815 contigs. Repeat analysis identified 3.91% repetitive elements, mainly SINEs, while variant calling detected more than 23,000 variants. Comparative analyses mapped several contigs to the swamp buffalo Y chromosome and Y-linked genes. Annotation against the B. taurus genome identified 26 unique genes, including homologs shared with the X chromosome, and revealed MSY gene duplications, including 10 copies of TSPY and 3 of HSFY. Conclusions: These findings show that laser microdissection with NGS enables effective access to the buffalo Y chromosome, representing a milestone in the characterization of the river type genome, and providing a basis for studies on buffalo male fertility and breeding programs. Full article

As the hybrid offspring of cattle and yak, cattle–yaks suffer from male sterility, manifesting as cascading spermatogenic failure. Despite the Y chromosome’s pivotal role in spermatogenesis, the absence of a high-quality yak Y assembly has long impeded mechanistic understandings from this perspective. Here, a near-complete 42.4 Mb yak Y chromosome is constructed through a multi-stage assembly strategy that integrates de novo assembly with pangenome graph construction and Hi-C guided refinement. By developing a rigorously standardized gene annotation pipeline for precise cross-species comparison, we find that yaks have undergone a greater expansion of Y-linked ampliconic genes than cattle. Integrating this ampliconic landscape with short-read and full-length transcriptomics further demonstrates that yaks exhibit a drastic 2-to-4-fold increase in transcriptionally active copies of spermatogenesis-related ampliconic genes (including TSPY1, ZNF280BY, HSFY and PRAMEY) relative to cattle. Given negligible homology outside the pseudoautosomal region and conservation of key meiotic proteins, we propose a ‘cis-trans regulatory mismatch’ model driven by divergent Y-linked amplification as a working hypothesis to explain the primary genetic mechanism of cattle–yak male sterility. Together, these findings offer critical insights for addressing cattle–yak male sterility and establish the Y chromosome as an active driver of reproductive isolation beyond its traditional degenerate characterization. Full article

Background: Duplications involving Xp22.33, particularly within the pseudoautosomal region 1 (PAR1), are rare. While copy number variants (CNVs) involving SHOX, a dosage-sensitive gene in PAR1, are known to cause growth disorders, large duplications encompassing the entire PAR1 region and beyond show variable associations with skeletal and neurodevelopmental abnormalities. Duplication of the near-complete, isolated PAR1 with a comprehensive clinical description has not been reported. Case Presentation: We report a male patient with a 2.49 Mb duplication encompassing nearly the entire PAR1 region (chrX:200854–2692897, GRCh37). Clinical features included global developmental delay (GDD), autism spectrum disorder (ASD), recurrent seizures, hypotonia with joint hypermobility, dysmorphic features, and proportionate tall stature. The duplicated segment contains 30 genes, including 15 protein-coding genes that escape X-inactivation. Among these, SHOX, DHRSX, ASMT, and CSF2RA are notable candidates contributing to the observed phenotype. Conclusions: This report presents a detailed clinical characterization of a rare, near-complete, isolated PAR1 duplication in a male individual. The co-occurrence of tall stature, GDD, ASD, and seizures raises the possibility of a dosage-related phenotypic effect involving one or more genes within the duplicated interval. While causality cannot be definitively established, these observations contribute to the emerging understanding of the functional consequences of Xp22.33 duplications and suggest that increased copy number within this region may be associated with a clinically significant neurodevelopmental phenotype. Full article

The SHOX gene is located on both sex chromosomes, X and Y, within the pseudoautosomal region 1 (PAR1). Gross deletions at the SHOX locus lead to protein insufficiency and are manifested by growth disorders such as Leri-Weill dyschondrosteosis (LWD), Langer mesomelic dysplasia (LMD), and idiopathic short stature (ISS). In cases of the SHOX gene duplication, the phenotype may range from tall to short stature and LWD. This study describes a family with various SHOX locus alterations and diverse phenotypic manifestations. The proband inherited both deletion and duplication in the SHOX locus from her parents and shows typical features of LWD. The proband’s father carries SHOX gene deletion and displays Madelung’s deformity but normal height. The proband’s mother has SHOX gene duplication without any abnormalities in phenotype. One of the proband’s sons inherited deletion, while the other inherited duplication of the gene. Some family members also have the c.845_851dup variant in the CYP26C1 gene, previously described as a modifier of the SHOX gene. It is difficult to assess its effect. At present, it is not possible to predict the future phenotype of the proband’s children due to the high phenotypic variability associated with SHOX locus alterations. Full article

Spinach is a dioecious vegetable and an excellent model for investigating plant sex differentiation. Exogenous gibberellin treatment induced sepal hypoplasia and sex reversal, converting 42% of stamens into pistils in male plants. Transcriptome analysis identified 112 male-biased genes enriched in stamen and pollen development, while hormone profiling revealed coordinated changes in GA, cytokinins, auxin, jasmonic acid, and abscisic acid. Functional assays demonstrated that silencing SpAMS or SpPGIP caused extensive carpelization, and in situ hybridization localized their expression to developing anthers. Dual-luciferase assays confirmed that SpAMS directly activates the B-class gene SpPI, and genomic mapping placed SpAMS in the pseudo-autosomal region of the Y chromosome. These results indicate that GA disrupts hormonal homeostasis and anther wall integrity, while the SpAMS–SpPI pathway regulates tapetal development to maintain male identity. Our findings identify SpAMS as a key male-promoting factor in spinach and provide a framework for elucidating sex determination mechanisms in dioecious plants. Full article

Probasin protein was originally identified as a basic protein present in rat prostate epithelium. So far, its physiological role, its origin, and its presence in other species including humans remain largely elusive. With the ever-growing number of genome assemblies, thus far, probasin genes (Pbsn/PBSN) have only been predicted in a subset of rodent genomes. In this study, we addressed the phylogeny of probasin genes and found them to be exclusively present in members of the superfamily Muroidea. It first emerged in the so-called pseudoautosomal region, a subtelomeric gene cluster of both mammalian sex chromosomes. During evolution of the Muroidea lineages, probasin recombined to the X-specific region of the X-chromosome in mice and hamster species. This event likely saved the gene from events that other pseudoautosomal genes suffered, namely displaying an increase in G and C nucleotide composition or accumulation of repetitive elements. We observed changes to its coding region, e.g., sequence insertions in exon 6, which challenge the current understanding of rodent phylogeny, in particular regarding the evolutionary history of tribe formation within the subfamily Murinae. Analyzing the evolution of probasin genes in Muroidea allows fostering understanding of phylogenetic relationships in one of the largest groups of mammalian species. Full article

Chromosome analysis (CA) and chromosomal microarray analysis (CMA) have been successfully used to diagnose genetic disorders. However, many conditions remain undiagnosed due to limitations in resolution (CA) and detection of only unbalanced events (CMA). Optical genome mapping (OGM) has the potential to address these limitations by capturing both structural variants (SVs) resulting in copy number changes and balanced rearrangements with high resolution. In this study, we investigated OGM’s concordance using 87 SVs previously identified by CA, CMA, or Southern blot. Overall, OGM was 98% concordant with only three discordant cases: (1) uncalled translocation with one breakpoint in a centromere; (2) uncalled duplication with breakpoints in the pseudoautosomal region 1; and (3) uncalled mosaic triplication originating from a marker chromosome. OGM provided diagnosis for three previously unsolved cases: (1) disruption of the SON gene due to a balanced reciprocal translocation; (2) disruption of the NBEA gene due to an inverted insertion; (3) disruption of the TSC2 gene due to a mosaic deletion. We show that OGM is a valid method for the detection of many types of SVs in a single assay and is highly concordant with legacy cytogenomic methods; however, it has limited SV detection capabilities in centromeric and pseudoautosomal regions. Full article

SHOX deficiency is a common genetic cause of short stature of variable degree. SHOX haploinsufficiency causes Leri–Weill dyschondrosteosis (LWD) as well as nonspecific short stature. SHOX haploinsufficiency is known to result from heterozygous loss-of-function variants with pseudo-autosomal dominant inheritance, while biallelic SHOX loss-of-function variants cause the more severe skeletal dysplasia, Langer mesomelic dyschondrosteosis (LMD). Here we report for the first time the pseudo-autosomal recessive inheritance of LWD in two siblings caused by a novel homozygous non-canonical, leaky splice-site variant in intron 3 of SHOX: c.544+5G>C. Transcript analyses in patient-derived fibroblasts showed homozygous patients to produce approximately equal amounts of normally spliced mRNA and mRNA with the abnormal retention of intron 3 and containing a premature stop codon (p.Val183Glyfs*31). The aberrant transcript was shown to undergo nonsense-mediated mRNA decay, and thus resulting in SHOX haploinsufficiency in the homozygous patient. Six healthy relatives who are of normal height are heterozygous for this variant and fibroblasts from a heterozygote for the c.544+5G>C variant produced wild-type transcript amounts comparable to healthy control. The unique situation reported here highlights the fact that the dosage of SHOX determines the clinical phenotype rather than the Mendelian inheritance pattern of SHOX variants. This study extends the molecular and inheritance spectrum of SHOX deficiency disorder and highlights the importance of functional testing of SHOX variants of unknown significance in order to allow appropriate counseling and precision medicine for each family individual. Full article

The chicken D blood system is one of 13 alloantigen systems found on chicken red blood cells. Classical recombinant studies located the D blood system on chicken chromosome 1, but the candidate gene was unknown. Multiple resources were utilized to identify the chicken D system candidate gene, including genome sequence information from both research and elite egg production lines for which D system alloantigen alleles were reported, and DNA from both pedigree and non-pedigree samples with known D alleles. Genome-wide association analyses using a 600 K or a 54 K SNP chip plus DNA from independent samples identified a strong peak on chicken chromosome 1 at 125–131 Mb (GRCg6a). Cell surface expression and the presence of exonic non-synonymous SNP were used to identify the candidate gene. The chicken CD99 gene showed the co-segregation of SNP-defined haplotypes and serologically defined D blood system alleles. The CD99 protein mediates multiple cellular processes including leukocyte migration, T-cell adhesion, and transmembrane protein transport, affecting peripheral immune responses. The corresponding human gene is found syntenic to the pseudoautosomal region 1 of human X and Y chromosomes. Phylogenetic analyses show that CD99 has a paralog, XG, that arose by duplication in the last common ancestor of the amniotes. Full article

Transmission ratio distortion (TRD), or significant deviations from Mendelian inheritance, is a well-studied phenomenon on autosomal chromosomes, but has not yet received attention on sex chromosomes. TRD was analyzed on 3832 heterosomal single nucleotide polymorphisms (SNPs) and 400 pseudoautosomal SNPs spanning the length of the X-chromosome using 436,651 genotyped Holstein cattle. On the pseudoautosomal region, an opposite sire-TRD pattern between male and female offspring was identified for 149 SNPs. This finding revealed unique SNPs linked to a specific-sex (Y- or X-) chromosome and describes the accumulation of recombination events across the pseudoautosomal region. On the heterosomal region, 13 SNPs and 69 haplotype windows were identified with dam-TRD. Functional analyses for TRD regions highlighted relevant biological functions responsible to regulate spermatogenesis, development of Sertoli cells, homeostasis of endometrium tissue and embryonic development. This study uncovered the prevalence of different TRD patterns across both heterosomal and pseudoautosomal regions of the X-chromosome and revealed functional candidate genes for bovine reproduction. Full article

The sex-linked region (SLR) plays an important role in determining the sex of a plant. The SLR of the Y chromosome, composed of a 14.1-Mb inversion and a 10-Mb Y-duplication region (YDR), was deciphered in Spinacia oleracea previously. However, our understanding of the SLR in its wild relatives, S. turkestanica and S. tetrandra, remains limited. In this study, we used 63 resequencing data from the three Spinacia species to infer the evolution of the SLR among the Spinacia species. In the SLR, all the cultivated spinach and S. turkestanica accessions were clustered into two distinct categories with both sexes, while the S. tetrandra accessions of both sexes were grouped. This suggests that S. oleracea shared a similar SLR with S. turkestanica, but not with S. tetrandra, which was further confirmed based on the population structure and principal component analysis. Furthermore, we identified 3910 fully sex-linked SNPs in S. oleracea and 92.82% of them were available in S. turkestanica, while none of the SNPs were adopted in S. tetrandra. Genome coverage in males and females supported the hypothesis that the YDR increasingly expanded during its evolution. Otherwise, we identified 13 sex-linked transposable element insertion polymorphisms within the inversion in both S. oleracea and S. turkestanica, demonstrating that the transposable element insertions might have occurred before the recombination suppression event of the inversion. The SLR was conserved compared with the pseudoautosomal region given that the genetic hitchhiking process occurred in the SLR during its evolution. Our findings will significantly advance our understanding of the characteristics and evolution of the SLR in Spinacia species. Full article

The conspicuous colour sexual dimorphism of guppies has made them paradigmatic study objects for sex-linked traits and sex chromosome evolution. Both the X- and Y-chromosomes of the common guppy (Poecilia reticulata) are genetically active and homomorphic, with a large homologous part and a small sex specific region. This feature is considered to emulate the initial stage of sex chromosome evolution. A similar situation has been documented in the related Endler’s and Oropuche guppies (P. wingei, P. obscura) indicating a common origin of the Y in this group. A recent molecular study in the swamp guppy (Micropoecilia. picta) reported a low SNP density on the Y, indicating Y-chromosome deterioration. We performed a series of cytological studies on M. picta to show that the Y-chromosome is quite small compared to the X and has accumulated a high content of heterochromatin. Furthermore, the Y-chromosome stands out in displaying CpG clusters around the centromeric region. These cytological findings evidently illustrate that the Y-chromosome in M. picta is indeed highly degenerated. Immunostaining for SYCP3 and MLH1 in pachytene meiocytes revealed that a substantial part of the Y remains associated with the X. A specific MLH1 hotspot site was persistently marked at the distal end of the associated XY structure. These results unveil a landmark of a recombining pseudoautosomal region on the otherwise strongly degenerated Y chromosome of M. picta. Hormone treatments of females revealed that, unexpectedly, no sexually antagonistic color gene is Y-linked in M. picta. All these differences to the Poecilia group of guppies indicate that the trajectories associated with the evolution of sex chromosomes are not in parallel. Full article

Avian sex chromosomes evolved after the divergence of birds and crocodilians from their common ancestor, so they are younger than the better-studied chromosomes of mammals. It has long been recognized that there may have been several stages to the evolution of avian sex chromosomes. For example, the CHD1 undergoes recombination in paleognaths but not neognaths. Genome assemblies have suggested that there may be variation in the timing of barriers to recombination among Neognathae, but there remains little understanding of the extent of this variability. Here, we look at partial sequences of ATP5F1A, which is on the avian Z and W chromosomes. It is known that recombination of this gene has independently ceased in Galliformes, Anseriformes, and at least five neoavian orders, but whether there are other independent cessations of recombination among Neoaves is not understood. We analyzed a combination of data extracted from published chromosomal-level genomes with data collected using PCR and cloning to identify Z and W copies in 22 orders. Our results suggest that there may be at least 19 independent cessations of recombination within Neognathae, and 3 clades that may still be undergoing recombination (or have only recently ceased recombination). Analyses of ATP5F1A protein sequences revealed an increased amino acid substitution rate for W chromosome gametologs, suggesting relaxed purifying selection on the W chromosome. Supporting this hypothesis, we found that the increased substitution rate was particularly pronounced for buried residues, which are expected to be more strongly constrained by purifying selection. This highlights the dynamic nature of avian sex chromosomes, and that this level of variation among clades means they should be a good system to understand sex chromosome evolution. Full article

In this article, we attempt to classify a potential dimorphism of melatonin production. Thus, a new concept of “reserve or maximum capacity of melatonin synthetic function” is introduced to explain the subtle dimorphism of melatonin production in mammals. Considering ASMT/ASMTL genes in the pseudoautosomal region of sex chromosomes with high prevalence of mutation in males, as well as the sex bias of the mitochondria in which melatonin is synthesized, we hypothesize the existence of a dimorphism in melatonin production to favor females, which are assumed to possess a higher reserve capacity for melatonin synthesis than males. Under physiological conditions, this subtle dimorphism is masked by the fact that cells or tissues only need baseline melatonin production, which can be accomplished without exploiting the full potential of melatonin’s synthetic capacity. This capacity is believed to exceed the already remarkable nocturnal increase as observed within the circadian cycle. However, during aging or under stressful conditions, the reserve capacity of melatonin’s synthetic function is required to be activated to produce sufficiently high levels of melatonin for protective purposes. Females seem to possess a higher reserve/maximum capacity for producing more melatonin than males. Thus, this dimorphism of melatonin production becomes manifest and detectable under these conditions. The biological significance of the reserve/maximum capacity of melatonin’s synthetic function is to improve the recovery rate of organisms from injury, to increase resistance to pathogen infection, and even to enhance their chances of survival by maximizing melatonin production under stressful conditions. The higher reserve/maximum capacity of melatonin synthesis in females may also contribute to the dimorphism in longevity, favoring females in mammals. Full article