Biology subjects

Samollow, P. B.

Publications and source records attributed to Samollow, P. B..

4 recordsLinked to original sources

bioRxiv2024

Low mutation rate but high male-bias in the germline of a short-lived opossum

Age and sex have been found to be important determinants of the mutation rate per generation in mammals, but the mechanisms underlying these factors are still unclear. One approach to distinguishing between alternative mechanisms is to study species that reproduce at very young ages, as competing hypotheses make different predictions about patterns of mutation in these organisms. Here, we study the germline mutation rate in the gray short-tailed opossum, Monodelphis domestica, a laboratory model species that becomes reproductively mature at less than six months of age. Whole-genome sequencing of 22 trios reveals the lowest mutation rate per generation found in mammals thus far (0.26 x 10-8 per base pair per generation at an average parental age of 313 days), which is expected given their early reproduction. We also examine the mutation spectrum and find fewer mutations at CpG sites in opossums than in humans, consistent with the lower CpG content in the opossum genome. We observe that two-thirds of mutations are inherited from the male parent in opossums, slightly lower than the degree of male bias observed in organisms that reproduce at much older ages. Nevertheless, the very young age at reproduction in opossums suggests that ongoing spermatogonial divisions in males after puberty are not the primary driver of the observed male mutation bias. These findings contribute to a growing body of evidence that the differences between male and female germline mutation may arise from mechanisms other than cell division post-puberty. Article SummaryThis study investigates the germline mutation rate in the gray short-tailed opossum, a marsupial with early reproductive maturity. By sequencing 22 families, we report the lowest mutation rate recorded in mammals but a typical male mutation bias. These findings add to growing evidence that challenges the traditional view that continuing cell division is the primary driver of male-biased mutations. Instead, the study suggests that alternative mechanisms, such as differences in DNA repair, may influence sex-specific mutation rates.

evolutionary biology↗

bioRxiv2021

Genetic and genomic architecture in eight strains of the laboratory opossum Monodelphis domestica

The gray short-tailed opossum is an established laboratory-bred marsupial model for biomedical research. It serves as a critical species for comparative genomics research, providing the pivotal phylogenetic outgroup for studies of derived vs. ancestral states of genomic/epigenomic characteristics for all eutherian mammal lineages. To characterize the current genetic profile of this laboratory marsupial, we examined 79 individuals from eight established laboratory strains. Double digest restriction-site associated DNA sequencing (ddRAD-seq) and whole-genome resequencing experiments were performed to investigate the genetic architecture in these strains. A total of 66,640 high-quality single nucleotide polymorphisms (SNPs) were identified. We analyzed SNP density, average heterozygosity, nucleotide diversity, and population differentiation parameter Fst within and between the eight strains. Principal component and population structure analysis clearly resolve the strains at the level of their ancestral founder populations, and the genetic architecture of these strains correctly reflects their breeding history. We confirmed the successful establishment of the first inbred laboratory opossum strain LSD (inbreeding coefficient F > 0.99) and a nearly inbred strain FD2M1 (0.98 < F < 0.99), each derived from a different ancestral background. These strains are suitable for various experimental protocols requiring controlled genetic backgrounds and for intercrosses and backcrosses that can generate offspring with informative SNPs for studying a variety of genetic and epigenetic processes. Together with recent advances in reproductive manipulation and CRISPR/Cas9 techniques for M. domestica, the existence of distinctive inbred strains will enable genome editing on different genetic backgrounds, greatly expanding the utility of this marsupial model for biomedical research.

genomics↗

bioRxiv2020

Conservation of glutathione S-transferase mRNA and protein sequences similar to human and horse Alpha class GST A3-3 across dog, goat, and opossum species

Recently, the glutathione S-transferase A3-3 (GST A3-3) homodimeric enzyme was identified as the most efficient enzyme that catalyzes isomerization of the precursors of testosterone, estradiol, and progesterone in the gonads of humans and horses. However, the presence of GST A3-3 orthologs with equally high ketosteroid isomerase activity has not been verified in other mammalian species, even though pig and cattle homologs have been cloned and studied. Identifying GSTA3 genes is a challenge because of multiple GSTA gene duplications (12 in the human genome), so few genomes have a corresponding GSTA3 gene annotated. To improve our understanding of GSTA3 gene products and their functions across diverse mammalian species, we cloned homologs of the horse and human GSTA3 mRNAs from the testes of a dog, goat, and gray short-tailed opossum, with those current genomes lacking GSTA3 gene annotations. The resultant novel GSTA3 mRNA and inferred protein sequences had a high level of conservation with human GSTA3 mRNA and protein sequences ([≥] 70% and [≥] 64% identities, respectively). Sequence conservation was also apparent for the 13 residues of the "H-site" in the 222 amino acid GSTA3 protein that is known to interact with the steroid substrates. Modeling predicted that the dog GSTA3-3 is a more active ketosteroid isomerase than the goat or opossum enzymes. Our results help us understand the active sites of mammalian GST A3-3 enzymes, and their inhibitors may be useful for reducing steroidogenesis for medical purposes, such as fertility control or treatment of steroid-dependent diseases.

molecular biology↗

bioRxiv2019

Non-linear sequence similarity between the Xist and Rsx long noncoding RNAs suggests shared functions of tandem repeat domains

The marsupial inactive X chromosome expresses a long noncoding RNA (lncRNA) called Rsx that has been proposed to be the functional analogue of eutherian Xist. Despite the possibility that Xist and Rsx encode related functions, the two lncRNAs harbor no linear sequence similarity. However, both lncRNAs harbor domains of tandemly repeated sequence. In Xist, these repeat domains are known to be critical for function. Using k-mer based comparison, we show that the repeat domains of Xist and Rsx unexpectedly partition into two major clusters that each harbor substantial levels of non-linear sequence similarity. Xist Repeats B, C and D were most similar to each other and to Rsx Repeat 1, whereas Xist Repeats A and E were most similar to each other and to Rsx Repeats 2, 3, and 4. Similarities at the level of k-mers corresponded to domain-specific enrichment of protein-binding motifs. Within individual domains, protein-binding motifs were often enriched to extreme levels. Our data support the hypothesis that Xist and Rsx encode similar functions through different spatial arrangements of functionally analogous protein-binding domains. We propose that the two clusters of repeat domains in Xist and Rsx function in part to cooperatively recruit PRC1 and PRC2 to chromatin. The physical manner in which these domains engage with protein cofactors may be just as critical to the function of the domains as the protein cofactors themselves. The general approaches we outline in this report should prove useful in the study of any set of RNAs.

genetics↗