Biology subjects

Halabian, R.

Publications and source records attributed to Halabian, R..

5 recordsLinked to original sources

bioRxiv2024

Exploring Alu-Driven DNA Transductions in the Primate Genomes

Long terminal repeats (LTRs) and non-LTRs retrotransposons, aka retroelements, collectively occupy a substantial part of the human genome. Certain non-LTR retroelements, such as L1 and SVA, have the potential for DNA transduction, which involves the concurrent mobilization of flanking non-transposon DNA during retrotransposition. These events can be detected by computational approaches. Despite being the most abundant short interspersed sequences (SINEs) that are still active within the genomes of humans and other primates, the transduction rate caused by Alu sequences remains unexplored. Therefore, we conducted an analysis to address this research gap and utilized an in-house program to probe for the presence of Alu-related transductions in the human genome. We analyzed 118,489 full-length AluY subfamilies annotated within the first complete human reference genome, T2T-CHM13. For comparative insights, we extended our exploration to two non-human primate genomes, the chimpanzee and the rhesus monkey. After manual curation, our findings did not confirm any Alu-mediated transductions, whose source genes are, unlike L1 or SVA, transcribed by RNA polymerase III, implying that they are infrequent or possibly absent not only in the human but also in chimpanzee and rhesus monkey genomes. Although we identified loci in which the 3 Target Site Duplication (TSD) was located distantly from the retrotransposed AluYs, a transduction hallmark, our study could not find further support for such events. The observation of these instances can be explained by the incorporation of other nucleotides into the poly(A) tails in conjunction with polymerase slippage.

genetics↗

bioRxiv2023

First cleavage is a manifestation of the geometry of the unfertilized oocyte: implications for monozygotic twinning in mice.

A long-standing question in mammalian embryology is whether regional differences of oocyte composition matter for the properties of blastomeres receiving those regions after fertilization. A hitherto untested hypothesis is that allocation depends on the orientation of 1st cleavage. However, the orientation is influenced by the site of sperm entry, which can be almost anywhere on the membrane of oocytes when these are inseminated. This variability undermines consistency and reproducibility of studies. Therefore, we harnessed the intracytoplasmic sperm injection to impose the site of fertilization in three specific ooplasmic regions (animal pole, vegetal pole, equator) in mice. Notwithstanding this categorical distinction, after 1st cleavage, the sister blastomeres differed from each other nearly the same way, as measured by gene expression and twin blastocysts formation following 2-cell embryo splitting. We reasoned that either the oocyte territories did not matter, or their effect was obscured by other factors. To shed light on these possibilities, we immobilized the oocytes on the micromanipulation stage during sperm injection and for 24 h thereafter. Imaging revealed that the orientation of 1st cleavage, instead of varying with the fertilization site, followed the shorter diameter of the unfertilized oocyte. This led in most cases to the segregation of animal and vegetal hemispheres into the sister blastomeres of 2-cell embryos. Since one blastomere received more of the animal materials and the other blastomere more of the vegetal materials, this offers a rationale to explain the distinct properties of monozygotic twins derived from 2-cell embryos in mice.

developmental biology↗

bioRxiv2022

The complete sequence of a human Y chromosome

The human Y chromosome has been notoriously difficult to sequence and assemble because of its complex repeat structure including long palindromes, tandem repeats, and segmental duplications1-3. As a result, more than half of the Y chromosome is missing from the GRCh38 reference sequence and it remains the last human chromosome to be finished4, 5. Here, the Telomere-to-Telomere (T2T) consortium presents the complete 62,460,029 base pair sequence of a human Y chromosome from the HG002 genome (T2T-Y) that corrects multiple errors in GRCh38-Y and adds over 30 million base pairs of sequence to the reference, revealing the complete ampliconic structures of TSPY, DAZ, and RBMY gene families; 41 additional protein-coding genes, mostly from the TSPY family; and an alternating pattern of human satellite 1 and 3 blocks in the heterochromatic Yq12 region. We have combined T2T-Y with a prior assembly of the CHM13 genome4 and mapped available population variation, clinical variants, and functional genomics data to produce a complete and comprehensive reference sequence for all 24 human chromosomes.

genomics↗

bioRxiv2021

From telomere to telomere: the transcriptional and epigenetic state of human repeat elements

Mobile elements and highly repetitive genomic regions are potent sources of lineage-specific genomic innovation and fingerprint individual genomes. Comprehensive analyses of large, composite or arrayed repeat elements and those found in more complex regions of the genome require a complete, linear genome assembly. Here we present the first de novo repeat discovery and annotation of a complete human reference genome, T2T-CHM13v1.0. We identified novel satellite arrays, expanded the catalog of variants and families for known repeats and mobile elements, characterized new classes of complex, composite repeats, and provided comprehensive annotations of retroelement transduction events. Utilizing PRO-seq to detect nascent transcription and nanopore sequencing to delineate CpG methylation profiles, we defined the structure of transcriptionally active retroelements in humans, including for the first time those found in centromeres. Together, these data provide expanded insight into the diversity, distribution and evolution of repetitive regions that have shaped the human genome.

genomics↗

bioRxiv2020

High-Quality Genome Assembly and Annotation of the California Harvester Ant Pogonomyrmex californicus (Buckley, 1867)

The harvester ant genus Pogonomyrmex is endemic to arid and semiarid habitats and deserts of North and South America and California harvester ant Pogonomyrmex californicus is the most widely distributed Pogonomyrmex species in the North America. P. californicus colonies are usually monogynous, i.e. a colony has one queen. However, in a few populations in California, primary polygyny evolved, i.e. several queens cooperate in colony founding after their mating flights and continue to coexist in mature colonies. Here, we present high quality genome assembly and annotation of P. californicus. The size of the assembly is 241 Mb, which is in good agreement with previously estimated genome size and we were able to annotate 17,889 genes in total, including 15,688 protein-coding ones with BUSCO completeness at the 95% level. This high quality genome will pave the way for investigations of the genomic underpinnings of social polymorphism in queen number, regulation of aggression, and the evolution of adaptations to dry habitats in P. californicus.

genomics↗