An efficient microinjection method for unfertilized eggs of Asian amphioxus Branchiostoma belcheri

Easy-to-Use CRISPR-Cas9 Genome Editing in the Cultured Pacific Abalone (Haliotis discus hannai)

The Pacific abalone is an important aquaculture shellfish and serves as an important model in basic biology study. However, the study of abalone is limited by lack of highly efficient and easy-to-use gene-editing tools. In this paper, we demonstrate efficient gene knockout in Pacific abalone using CRISPR-Cas9. We developed a highly effective microinjection method by nesting fertilized eggs in a low-concentration agarose gel. We identified the cilia developmental gene β-tubulin and light-sensitive transmembrane protein r-opsin as target genes and designed highly specific sgRNAs for modifying their genomic sequences. Sanger sequencing of the genomic regions of β-tubulin and r-opsin genes from injected larvae identified various genomic long-fragment deletions. In situ hybridization showed gene expression patterns of β-tubulin and r-opsin were significantly altered in the mosaic mutants. Knocking out β-tubulin in abalone embryos efficiently affected cilia development. Scanning electron microscopy and swimming behavior assay showed defecting cilia and decreased motility. Moreover, knocking out of r-opsin in abalone embryos effectively affected the expression and development of eyespots. Overall, this work developed an easy-to-use mosaic gene knockout protocol for abalone, which will allow researchers to utilize CRISPR-Cas9 approaches to study unexploited abalone biology and will lead to novel breeding methods for this aquaculture species.

Evolution of the gene regulatory network of body axis by enhancer hijacking in amphioxus

A central goal of evolutionary developmental biology is to decipher the evolutionary pattern of gene regulatory networks (GRNs) that control embryonic development, and the mechanism underlying GRNs evolution. The Nodal signaling that governs the body axes of deuterostomes exhibits a conserved GRN orchestrated principally by Nodal, Gdf1/3, and Lefty. Here we show that this GRN has been rewired in cephalochordate amphioxus. We found that while the amphioxus Gdf1/3 ortholog exhibited nearly no embryonic expression, its duplicate Gdf1/3-like, linked to Lefty, was zygotically expressed in a similar pattern as Lefty. Consistent with this, while Gdf1/3-like mutants showed defects in axial development, Gdf1/3 mutants did not. Further transgenic analyses showed that the intergenic region between Gdf1/3-like and Lefty could drive reporter gene expression as that of the two genes. These results indicated that Gdf1/3-like has taken over the axial development role of Gdf1/3 in amphioxus, possibly through hijacking Lefty enhancers. We finally demonstrated that, to compensate for the loss of maternal Gdf1/3 expression, Nodal has become an indispensable maternal factor in amphioxus and its maternal mutants caused axial defects as Gdf1/3-like mutants. We therefore demonstrated a case that the evolution of GRNs could be triggered by enhancer hijacking events. This pivotal event has allowed the emergence of a new GRN in extant amphioxus, presumably through a stepwise process. In addition, the co-expression of Gdf1/3-like and Lefty achieved by a shared regulatory region may have provided robustness during body axis formation, which provides a selection-based hypothesis for the phenomena called developmental system drift.

Amphioxus Gli knockout disrupts the development of left-right asymmetry but has limited impact on neural patterning

The Gli transcription factors are the primary mediators of Hedgehog (Hh) signaling. Vertebrate genomes contain multiple Gli paralogues with different functions downstream of Hh signal receipt, in part explaining the complexity of cellular responses to Hh that allow concentration-dependent target gene activation. Amphioxus is a chordate that split from the vertebrate lineage early in the evolution of chordates, before the genome duplications that occurred in early vertebrate evolution. It has a single Gli gene whose transcripts can be alternately spliced to yield two protein isoforms called GliS and GliL. We generated two knockout mutations in amphioxus Gli, one that affects the whole gene and a second that only affects GliL. Both knockouts showed major morphological and molecular defects in the development of left-right asymmetry, a phenotype that is similar but not identical to that previously found in Hh mutants. Hh signaling also patterns the amphioxus neural tube. Here, however, knockout of GliL showed no identifiable phenotype, while knockout of the full gene showed only small changes to the expression of one gene family, Olig. Other genes that were prominently affected by Hh knockout were not altered in expression in either knockout. Reasons for the differences between Hh and Gli knockouts in the pharynx and neural tube are discussed in the context of the likely different functions of amphioxus Gli isoforms.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-023-00195-w.

Joint profiling of gene expression and chromatin accessibility during amphioxus development at single-cell resolution

Vertebrate evolution was accompanied by two rounds of whole-genome duplication followed by functional divergence in terms of regulatory circuits and gene expression patterns. As a basal and slow-evolving chordate species, amphioxus is an ideal paradigm for exploring the origin and evolution of vertebrates. Single-cell sequencing has been widely used to construct the developmental cell atlas of several representative species of vertebrates (human, mouse, zebrafish, and frog) and tunicates (sea squirts). Here, we perform single-nucleus RNA sequencing (snRNA-seq) and single-cell assay for transposase accessible chromatin sequencing (scATAC-seq) for different stages of amphioxus (covering embryogenesis and adult tissues). With the datasets generated, we constructed a developmental tree for amphioxus cell fate commitment and lineage specification and characterize the underlying key regulators and genetic regulatory networks. The data are publicly available on the online platform AmphioxusAtlas.

A Potential Method for Rapid Screening of Amphioxus Founder Harboring Germline Mutation and Transgene

Amphioxus is a promising model organism for understanding the origin and evolution of vertebrates due to its basal phylogenetic position among chordates. We here compared the mutation efficacy and mutation type of tail tips and gametes of amphioxus founders injected with Cas9 protein and six different sgRNAs targeting five distinct genes, and revealed a strong correlation for mutation efficacy and a mild correlation for mutation type among the two tissues. In addition, we also observed a positive relationship between gene insertions observed in tail tips and gametes of amphioxus founders injected with Tol2 transposase and two different transgenic constructs. Finally, we showed that amphioxus larvae which had their tail tips cut at the 3-4 gill-slit stage were able to recover within 6 days and developed a normal number of gonads at the adult stage, and that F0 larvae carry similar mutation efficacy and type in the posterior end to that in the tail tips after their metamorphosis. Together, these findings suggest a great potential for obtaining valid amphioxus founders with desired mutations and transgenes at as early as the early larval stage, which will certainly speed up the generation of amphioxus mutants and transgenes and make it more cost- and labor-effective.

Pitx controls amphioxus asymmetric morphogenesis by promoting left-side development and repressing right-side formation

Background

Left-right (LR) asymmetry is an essential feature of bilateral animals. Studies in vertebrates show that LR asymmetry formation comprises three major steps: symmetry breaking, asymmetric gene expression, and LR morphogenesis. Although much progress has been made in the first two events, mechanisms underlying asymmetric morphogenesis remain largely unknown due to the complex developmental processes deployed by vertebrate organs.

Results

We here addressed this question by studying Pitx gene function in the basal chordate amphioxus whose asymmetric organogenesis, unlike that in vertebrates, occurs essentially in situ and does not rely on cell migration. Pitx null mutation in amphioxus causes loss of all left-sided organs and incomplete ectopic formation of all right-sided organs on the left side, whereas Pitx partial loss-of-function leads to milder phenotypes with only some LR organs lost or ectopically formed. At the N1 to N3 stages, Pitx expression is gradually expanded from the dorsal anterior domain to surrounding regions. This leads to activation of genes like Lhx3 and/or Prop1 and Pit, which are essential for left-side organs, and downregulation of genes like Hex and/or Nkx2.1 and FoxE4, which are required for right-side organs to form ectopically on the left side. In Pitx mutants, the left-side expressed genes are not activated, while the right-side genes fail to decrease expression on the left side. In contrast, in embryos overexpressing Pitx genes, the left-side genes are induced ectopically on the right side, and the right-side genes are inhibited. Several Pitx binding sites are identified in the upstream sequences of the left-side and right-side genes which are essential for activation of the former and repression of the latter by Pitx.

Conclusions

Our results demonstrate that (1) Pitx is a major (although not the only) determinant of asymmetric morphogenesis in amphioxus, (2) the development of different LR organs have distinct requirements for Pitx activity, and (3) Pitx controls amphioxus LR morphogenesis probably through inducing left-side organs and inhibiting right-side organs directly. These findings show much more dependence of LR organogenesis on Pitx in amphioxus than in vertebrates. They also provide insight into the molecular developmental mechanism of some vertebrate LR organs like the lungs and atria, since they show a right-isomerism phenotype in Pitx2 knockout mice like right-sided organs in Pitx mutant amphioxus. Our results also explain why some organs like the adenohypophysis are asymmetrically located in amphioxus but symmetrically positioned in vertebrates.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01095-0.

Laboratory Culture and Mutagenesis of Amphioxus (Branchiostoma floridae)

Cephalochordates (amphioxus) are invertebrate chordates closely related to vertebrates. As they are evolving very slowly, they are proving to be very appropriate for developmental genetics studies aimed at understanding how vertebrates evolved from their invertebrate ancestors. To date, techniques for gene knockdown and overexpression have been developed, but methods for continuous breeding cultures and generating germline mutants have been developed only recently. Here we describe methods for continuous laboratory breeding cultures of the cephalochordate Branchiostoma floridae and the TALEN and Tol2 methods for mutagenesis. Included are strategies for analyzing the mutants and raising successive generations to obtain homozygotes. These methods should be applicable to any warm water species of cephalochordates with a relatively short generation time of 3-4 months and a life span of 3 years or more.

Application of CRISPR/Cas9 Nuclease in Amphioxus Genome Editing

The cephalochordate amphioxus is a promising animal model for studying the origin of vertebrates due to its key phylogenetic position among chordates. Although transcription activator-like effector nucleases (TALENs) have been adopted in amphioxus genome editing, its labor-intensive construction of TALEN proteins limits its usage in many laboratories. Here we reported an application of the CRISPR/Cas9 system, a more amenable genome editing method, in this group of animals. Our data showed that while co-injection of Cas9 mRNAs and sgRNAs into amphioxus unfertilized eggs caused no detectable mutations at targeted loci, injections of Cas9 mRNAs and sgRNAs at the two-cell stage, or of Cas9 protein and sgRNAs before fertilization, can execute efficient disruptions of targeted genes. Among the nine tested sgRNAs (targeting five genes) co-injected with Cas9 protein, seven introduced mutations with efficiency ranging from 18.4% to 90% and four caused specific phenotypes in the injected embryos. We also demonstrated that monomerization of sgRNAs via thermal treatment or modifying the sgRNA structure could increase mutation efficacies. Our study will not only promote application of genome editing method in amphioxus research, but also provide valuable experiences for other organisms in which the CRISPR/Cas9 system has not been successfully applied.

Differential expression pattern of two Brachyury genes in amphioxus embryos

Cephalochordate amphioxus contain two Brachyury genes (AmphiBra1 and AmphiBra2). Using probes from the highly conserved coding regions, a summation of their expression profiles in amphioxus embryos have been investigated by several previous studies. However, their respective expression patterns have not been determined up to date. We here address this issue using both qRT-PCR and in situ hybridization methods (with probes from the divergent untranslated regions). qRT-PCR detected a very low maternal expression for AmphiBra2, but not for AmphiBra1. Zygotic expression of both genes are activated around early gastrula stage and change in a similar pattern at subsequent stages. However, compared to AmphiBra1, the expression level of AmphiBra2 is much higher in all examined stages of embryos; in some extreme cases an over fifty-times difference is observed. In situ hybridization and embryonic sections reveal that while AmphiBra2 is highly expressed in the blastopore, the tail bud and the notochord, AmphiBra1 is weakly transcribed only in the notochord. Our results show that the two Brachyury genes, resulted from a lineage-specific duplication in amphioxus, have evolved different embryonic expression profiles.

Mutation of amphioxus Pdx and Cdx demonstrates conserved roles for ParaHox genes in gut, anus and tail patterning

BACKGROUND

The homeobox genes Pdx and Cdx are widespread across the animal kingdom and part of the small ParaHox gene cluster. Gene expression patterns suggest ancient roles for Pdx and Cdx in patterning the through-gut of bilaterian animals although functional data are available for few lineages. To examine evolutionary conservation of Pdx and Cdx gene functions, we focus on amphioxus, small marine animals that occupy a pivotal position in chordate evolution and in which ParaHox gene clustering was first reported.

RESULTS

Using transcription activator-like effector nucleases (TALENs), we engineer frameshift mutations in the Pdx and Cdx genes of the amphioxus Branchiostoma floridae and establish mutant lines. Homozygous Pdx mutants have a defect in amphioxus endoderm, manifest as loss of a midgut region expressing endogenous GFP. The anus fails to open in homozygous Cdx mutants, which also have defects in posterior body extension and epidermal tail fin development. Treatment with an inverse agonist of retinoic acid (RA) signalling partially rescues the axial and tail fin phenotypes indicating they are caused by increased RA signalling. Gene expression analyses and luciferase assays suggest that posterior RA levels are kept low in wild type animals by a likely direct transcriptional regulation of a Cyp26 gene by Cdx. Transcriptome analysis reveals extensive gene expression changes in mutants, with a disproportionate effect of Pdx and Cdx on gut-enriched genes and a colinear-like effect of Cdx on Hox genes.

CONCLUSIONS

These data reveal that amphioxus Pdx and Cdx have roles in specifying middle and posterior cell fates in the endoderm of the gut, roles that likely date to the origin of Bilateria. This conclusion is consistent with these two ParaHox genes playing a role in the origin of the bilaterian through-gut with a distinct anus, morphological innovations that contributed to ecological change in the Cambrian. In addition, we find that amphioxus Cdx promotes body axis extension through a molecular mechanism conserved with vertebrates. The axial extension role for Cdx dates back at least to the origin of Chordata and may have facilitated the evolution of the post-anal tail and active locomotion in chordates.

Cilia-driven asymmetric Hedgehog signalling determines the amphioxus left-right axis by controlling Dand5 expression

Cilia rotation-driven nodal flow is crucial for the left-right (L-R) break in symmetry in most vertebrates. However, the mechanism by which the flow signal is translated to asymmetric gene expression has been insufficiently addressed. Here, we show that Hedgehog (Hh) signalling is asymmetrically activated (L<R) in the region in which initial asymmetric Dand5 expression is detected. Upregulation of Hh signalling on the left side of wild-type embryos induces ectopic Dand5 expression on the left side, and the unilateral recovery of Hh signalling in Hh homozygous mutants induces Dand5 expression in the Hh signal recovery side. Immunofluorescence analysis results revealed that Hh fusion protein is asymmetrically enriched in the anterior-right paraxial mesoderm at the early neurula stage. Inhibiting embryonic cilia motility using methylcellulose (MC) blocks Hh protein enrichment on the right hand side and randomizes Dand5 expression and organ positioning along the L-R axis. These findings present a model showing that cilia movement is crucial for the symmetry breaks in amphioxus through asymmetric Hh protein transport. The resultant asymmetric Hh signalling provides a clue into the induction of asymmetric Dand5 expression.This article has an associated 'The people behind the papers' interview.

An Effective Microinjection Method and TALEN-Mediated Genome Editing in Pacific Abalone

Pacific abalone, Haliotis discus hannai, is an economically important marine mollusk species and an important model animal for studies on ecological, fertilization and developmental biology. While embryonic injection and genome editing have been wildly used in gene function study and trait improvement in many species, they have not been developed in abalones. In this study, we reported an effective method to inject exogenous materials in H. discus hannai unfertilized eggs. The injected eggs could be fertilized at a ratio of 52.6% ± 5.9% and hatch at a ratio of 14.6% ± 1.6%. On the base of this, we further developed an efficient genome editing approach in this species with the transcription activator-like effector nuclease (TALEN) technique. Two TALEN pairs targeting the coding sequence of the abalone nodal gene were assembled and tested. While one of the TALEN pairs showed no detectable mutation efficacy, the other one generated mutations in 50% of the targeted loci. The mutation includes small insertions and deletions and base pair replacements like that reported in other species when the TALEN method was applied. Overall, this is the first study to demonstrate site-specific genome editing in abalone. This work can serve as a reference for future studies focusing on the functional genomics in mollusks.

Evolution of vertebrate spinal cord patterning

The vertebrate spinal cord is organized across three developmental axes, anterior-posterior (AP), dorsal-ventral (DV), and medial-lateral (ML). Patterning of these axes is regulated by canonical intercellular signaling pathways: the AP axis by Wnt, fibroblast growth factor, and retinoic acid (RA), the DV axis by Hedgehog, Tgfβ, and Wnt, and the ML axis where proliferation is controlled by Notch. Developmental time plays an important role in which signal does what and when. Patterning across the three axes is not independent, but linked by interactions between signaling pathway components and their transcriptional targets. Combined this builds a sophisticated organ with many different types of cell in specific AP, DV, and ML positions. Two living lineages share phylum Chordata with vertebrates, amphioxus, and tunicates, while the jawless fish such as lampreys, survive as the most basally divergent vertebrate lineage. Genes and mechanisms shared between lampreys and other vertebrates tell us what predated vertebrates, while those also shared with other chordates tell us what evolved early in chordate evolution. Between these lie vertebrate innovations: genetic and developmental changes linked to evolution of new morphology. These include gene duplications, differences in how signals are received, and new regulatory connections between signaling pathways and their target genes.

Overexpression of MicroRNA-29b Decreases Expression of DNA Methyltransferases and Improves Quality of the Blastocysts Derived from Somatic Cell Nuclear Transfer in Cattle

MicroRNA (miR)-29b plays a crucial role during somatic cell reprogramming. The aim of the current study was to explore the effects of miR-29b on the developmental competence of bovine somatic cell nuclear transfer (SCNT) embryos, as well as the underlying mechanisms of action. The expression level of miR-29b was lower in bovine SCNT embryos at the pronuclear, 8-cell, and blastocyst stages compared with in vitro fertilized embryos. In addition, miR-29b regulates the expression of DNA methyltransferases (Dnmt3a/3b and Dnmt1) in bovine SCNT embryos. We further investigated SCNT embryo developmental competence and found that miR-29b overexpression during bovine SCNT embryonic development does not improve developmental potency and downregulation inhibits developmental potency. Nevertheless, the quality of bovine SCNT embryos at the blastocyst stage improved significantly. The expression of pluripotency factors and cellular proliferation were significantly higher in blastocysts from the miR-29b overexpression group than the control and downregulation groups. In addition, outgrowth potential in blastocysts after miR-29b overexpression was also significantly greater in the miR-29b overexpression group than in the control and downregulation groups. Taken together, these results demonstrated that miR-29b plays an important role in bovine SCNT embryo development.

Hedgehog participates in the establishment of left-right asymmetry during amphioxus development by controlling Cerberus expression

Correct patterning of left-right (LR) asymmetry is essential during the embryonic development of bilaterians. Hedgehog (Hh) signaling is known to play a role in LR asymmetry development of mouse, chicken and sea urchin embryos by regulating Nodal expression. In this study, we report a novel regulatory mechanism for Hh in LR asymmetry development of amphioxus embryos. Our results revealed that Hh^-/- embryos abolish Cerberus (Cer) transcription, with bilaterally symmetric expression of Nodal, Lefty and Pitx In consequence, Hh^-/- mutants duplicated left-side structures and lost right-side characters, displaying an abnormal bilaterally symmetric body plan. These LR defects in morphology and gene expression could be rescued by Hh mRNA injection. Our results indicate that Hh participates in amphioxus LR patterning by controlling Cer gene expression. Curiously, however, upregulation of Hh signaling failed to alter the Cer expression pattern or LR morphology in amphioxus embryos, indicating that Hh might not provide an asymmetric cue for Cer expression. In addition, Hh is required for mouth opening in amphioxus, hinting at a homologous relationship between amphioxus and vertebrate mouth development.

Cerberus-Nodal-Lefty-Pitx signaling cascade controls left-right asymmetry in amphioxus

Many bilaterally symmetrical animals develop genetically programmed left-right asymmetries. In vertebrates, this process is under the control of Nodal signaling, which is restricted to the left side by Nodal antagonists Cerberus and Lefty. Amphioxus, the earliest diverging chordate lineage, has profound left-right asymmetry as a larva. We show that Cerberus, Nodal, Lefty, and their target transcription factor Pitx are sequentially activated in amphioxus embryos. We then address their function by transcription activator-like effector nucleases (TALEN)-based knockout and heat-shock promoter (HSP)-driven overexpression. Knockout of Cerberus leads to ectopic right-sided expression of Nodal, Lefty, and Pitx, whereas overexpression of Cerberus represses their left-sided expression. Overexpression of Nodal in turn represses Cerberus and activates Lefty and Pitx ectopically on the right side. We also show Lefty represses Nodal, whereas Pitx activates Nodal These data combine in a model in which Cerberus determines whether the left-sided gene expression cassette is activated or repressed. These regulatory steps are essential for normal left-right asymmetry to develop, as when they are disrupted embryos may instead form two phenotypic left sides or two phenotypic right sides. Our study shows the regulatory cassette controlling left-right asymmetry was in place in the ancestor of amphioxus and vertebrates. This includes the Nodal inhibitors Cerberus and Lefty, both of which operate in feedback loops with Nodal and combine to establish asymmetric Pitx expression. Cerberus and Lefty are missing from most invertebrate lineages, marking this mechanism as an innovation in the lineage leading to modern chordates.

The role of the Pax1/9 gene in the early development of amphioxus pharyngeal gill slits

The pharynx is a major characteristic of chordates. Compared with vertebrates, amphioxus has an advantage for the study of pharynx development, as embryos lack neural crest, and the pharynx is mainly derived from endoderm cells. The Pax1/9 subfamily genes have essential roles in vertebrate pharyngeal patterning, but it is not known if the Pax1/9 gene has similar functions in amphioxus pharynx development. To answer this question, we examined the Pax1/9 gene expression pattern in amphioxus embryos at different developmental stages, and observed morphological changes following Pax1/9 knockdown. RT-qPCR analysis indicated that Pax1/9 expression was initiated during early neurula stage and rapidly peaked during mid-neurula stage. Furthermore, in situ hybridization analysis showed that Pax1/9 transcripts were localized exclusively in the most endodermal region of the developing pharynx in early neurula stage embryos; however, Pax1/9 expression was strikingly down-regulated in the region where gill slits would form from the fusion of endoderm and ectoderm in subsequent developmental stages and was maintained in the border regions between adjacent gill slits. Knockdown of Pax1/9 function using both morpholino and siRNA approaches led to embryonic defects in the first three gill slits, and fusion of the first two gill slits. Moreover, the expression levels of the pharyngeal marker genes Six1/2 and Tbx1/10 were reduced in Pax1/9 knockdown embryos. From these observations, we concluded that the Pax1/9 gene has an important role in the initial differentiation of amphioxus pharyngeal endoderm and in the formation of gill slits, most likely via modulation of Six1/2 and Tbx1/10 expression.

Gene regulation in amphioxus: An insight from transgenic studies in amphioxus and vertebrates

Cephalochordates, commonly known as amphioxus or lancelets, are the most basal subphylum of chordates. Cephalochordates are thus key to understanding the origin of vertebrates and molecular mechanisms underlying vertebrate evolution. The evolution of developmental control mechanisms during invertebrate-to-vertebrate transition involved not only gene duplication events, but also specific changes in spatial and temporal expression of many genes. To get insight into the spatiotemporal regulation of gene expression during invertebrate-to-vertebrate transition, functional studies of amphioxus gene regulatory elements are highly warranted. Here, we review transgenic studies performed in amphioxus and vertebrates using promoters and enhancers derived from the genome of Branchiostoma floridae. We describe the current methods of transgenesis in amphioxus, provide evidence of Tol2 transposon-generated transgenic embryos of Branchiostoma lanceolatum and discuss possible future directions. We envision that comparative transgenic analysis of gene regulatory sequences in the context of amphioxus and vertebrate embryos will likely provide an important mechanistic insight into the evolution of vertebrate body plan.

Expression of fluorescent proteins in Branchiostoma lanceolatum by mRNA injection into unfertilized oocytes

We report here a robust and efficient protocol for the expression of fluorescent proteins after mRNA injection into unfertilized oocytes of the cephalochordate amphioxus, Branchiostoma lanceolatum. We use constructs for membrane and nuclear targeted mCherry and eGFP that have been modified to accommodate amphioxus codon usage and Kozak consensus sequences. We describe the type of injection needles to be used, the immobilization protocol for the unfertilized oocytes, and the overall injection set-up. This technique generates fluorescently labeled embryos, in which the dynamics of cell behaviors during early development can be analyzed using the latest in vivo imaging strategies. The development of a microinjection technique in this amphioxus species will allow live imaging analyses of cell behaviors in the embryo as well as gene-specific manipulations, including gene overexpression and knockdown. Altogether, this protocol will further consolidate the basal chordate amphioxus as an animal model for addressing questions related to the mechanisms of embryonic development and, more importantly, to their evolution.

Skin-derived mesenchymal stem cells help restore function to ovaries in a premature ovarian failure mouse model

Skin-derived mesenchymal stem cells (SMSCs) can differentiate into the three embryonic germ layers. For this reason, they are considered a powerful tool for therapeutic cloning and offer new possibilities for tissue therapy. Recent studies showed that skin-derived stem cells can differentiate into cells expressing germ-cell specific markers in vitro and form oocytes in vivo. The idea that SMSCs may be suitable for the treatment of intractable diseases or traumatic tissue damage has attracted attention. To determine the ability of SMSCs to reactivate injured ovaries, a mouse model with ovaries damaged by busulfan and cyclophosphamide was developed and is described here. Female skin-derived mesenchymal stem cells (F-SMSCs) and male skin-derived mesenchymal stem cells (M-SMSCs) from red fluorescence protein (RFP) transgenic adult mice were used to investigate the restorative effects of SMSCs on ovarian function. Significant increases in total body weight and the weight of reproductive organs were observed in the treated animals. Both F-SMSCs and M-SMSCs were shown to be capable of partially restoring fertility in chemotherapy-treated females. Immunostaining with RFP and anti-Müllerian hormone (AMH) antibodies demonstrated that the grafted SMSCs survived, migrated to the recipient ovaries. After SMSCs were administered to the treated mice, real-time PCR showed that the expression levels of pro-inflammatory cytokines TNF-α, TGF-β, IL-8, IL-6, IL-1β, and IFNγ were significantly lower in the ovaries than in the untreated controls. Consistent with this observation, expression of oogenesis marker genes Nobox, Nanos3, and Lhx8 increased in ovaries of SMSCs-treated mice. These findings suggest that SMSCs may play a role within the ovarian follicle microenvironment in restoring the function of damaged ovaries and could be useful in reproductive health.