Development Growth & Differentiation最新文献

Amphibians exhibit two remarkable biological phenomena: regeneration and metamorphosis. The ability to regenerate damaged body parts, such as the limbs, and to remodel organs—such as tail resorption during metamorphosis—is both fascinating and enigmatic. However, until recently, it has been difficult to manipulate gene expression in amphibians after embryogenesis, hindering molecular studies of these processes. Over the past two decades, the development of a simple and reproducible gene expression method—the heat-shock-inducible system—has helped overcome this limitation. This system involves generating transgenic animals carrying gene(s) of interest under the control of a heat shock promoter, typically the hsp70 promoter, followed by heat shock treatment to induce expression. Recent advancements have enabled not only the application of heat shock to the whole body but also spatially restricted gene induction in specific cell populations. In particular, laser irradiation allows for highly precise gene activation and lineage tracing, even at the single-cell level. One current limitation of this system is unintended “leaky” gene expression in the absence of heat shock. The recent availability of an alternative inducible system, Tet-on, in amphibians holds promise for overcoming this drawback and achieving tighter control of gene expression. In this review, we discuss potential refinements to the heat-shock-inducible system—including improvements in laser irradiation techniques and optimization of heat shock promoters (e.g., hsp70 promoter)—to address current limitations, and explore how this system may become an even more powerful tool for studying regeneration and metamorphosis in amphibians.

During anuran metamorphosis, rapid and extensive morphological transformations occur throughout the body, and these changes are triggered by the thyroid hormone. The thyroid hormone receptor (TR) is a nuclear receptor that is present in all vertebrates. TR binds specific DNA sequences to repress target genes in the absence of ligand and to activate them when ligand-bound. This dual regulatory function has been proposed to underlie the rapid pace of anuran metamorphosis. One TR subtype, TRα, suppresses hindlimb (HL) development in pre-metamorphic Xenopus tropicalis. However, the genes repressed by TRα remain unidentified, and it is unclear whether TRα-mediated developmental suppression occurs in specific organs. This study aimed to identify HL genes regulated by TRα during developmental suppression and to determine whether this suppression is widespread in the pre-metamorphic tadpole. We analyzed temporal changes in morphology and gene expression in the HL buds and intestines of TRα-knockout (KO) pre-metamorphic X. tropicalis tadpoles. HL buds appeared earlier in KO tadpoles than in the wild type. Whole-mount in situ hybridization showed that the interval from fertilization to initial expression of shh was shorter in KO HLs. However, the expression pattern in HL buds with comparable morphology was essentially identical between genotypes. On the other hand, there was no significant acceleration in the growth of the intestine or body (from snout to vent) of the KO tadpoles. Our findings suggest that unliganded TRα delays the onset of HL development prior to metamorphosis.

The corpus callosum (CC) is the large axon bundle connecting the telencephalic hemispheres. The CC is formed exclusively in placental mammals, and the lack of comparable structures in other amniotes obscures the evolutionary origin of the CC. We here demonstrate that interhemispheric remodeling, a prior developmental step for CC formation, is highly conserved in nonmammalian amniotes, such as reptiles and birds. In these animal groups, the spatio-temporal dynamics of interhemispheric remodeling are tightly connected with distinct commissural formations. We observed a high degree of similarity between the mammalian CC and reptilian rostral pallial commissure (RPC) and significant modifications in the avian pallial projection. Furthermore, we determined that Satb2 plays crucial roles in interhemispheric remodeling, which is associated with proper formation of both the CC and RPC in mice and geckoes, via the use of Clustered Regularly Interspaced Short Palindromic Repeat (CRISPR)-mediated gene targeting. Our findings suggest that developmental mechanisms for midline remodeling were already present in the common ancestor of amniotes, which contributed to the evolution of eutherian-specific CC formation.

Zinc finger protein 281 (Znf281) plays important roles in human malignancies, stem cell pluripotency, and placental and embryonic development. However, the function of Znf281 during early neural development remains unclear. Here, we investigated the role of Znf281 in the formation of neural tissue in Xenopus embryos. znf281 transcripts are expressed in the animal hemisphere of the embryo at the blastula and gastrula stages and gradually localize in neural tissue after gastrulation. Overexpression of Znf281 induces neural tissue with anterior–posterior patterning and inhibits epidermal differentiation in ectodermal explants and embryos. Mechanistically, Znf281 reduces the levels of phosphorylated Smad1/5/8 proteins, the downstream effectors of bone morphogenetic protein (BMP) signaling, to promote neural development. Moreover, knockdown of Znf281 in embryos results in the reduced expression of neural markers, indicating that Znf281 is required for early neural development. These results suggest that Znf281 plays an important role in the establishment of the central nervous system by modulating BMP signaling during vertebrate embryogenesis.

In medaka (Oryzias latipes), the first morphological sex difference is germ cell number before hatching, which is determined by the dmy gene on the Y chromosome. This study aimed to clarify whether zygotically synthesized estrogen influences the kinetics of germ cell number during early gonadal sex differentiation. We established disruptive mutants of the estrogen-synthesizing enzyme aromatase by knocking out cyp19a1a (Δcyp19a1a) and cyp19a1b (Δcyp19a1b) as well as double disruptive mutants (Δcyp19a1s DKO) from each individual knockout using CRISPR/Cas9. Δcyp19a1s DKO XY and XX adult fish at 90 days post-hatching (dph) exhibited basal levels of estradiol-17β. At hatching (0 dph: stage 39), WT XX fry had significantly more germ cells than WT XY fry, and gonial cells were the most advanced germ cell stage across both sexes. Germ cell number and gonadal histology in Δcyp19a1s DKO mutants resembled those of WT fry. At 10 dph, germ cell number and gonadal histology were also similar between WT and Δcyp19a1s XY fry. In Δcyp19a1s DKO XX fry, diplotene oocytes and the total number of germ cells were significantly lower compared with WT. Exposure to 17α-ethynylestradiol rescued the reduction in diplotene oocytes in Δcyp19a1s DKO mutants to levels comparable to the control, resulting in the rescue of total germ cell number. Overall, our findings suggest that zygotically synthesized estrogen does not affect sex differences in germ cell number as the initial morphological sex difference but partly facilitates the differentiation from pachytene to diplotene oocytes.

Plant growth is intricately linked to the development of a robust and extensive root system, a process that is finely tuned by the plant's ability to sense and respond to environmental nutrient cues. Among these, nitrate and photosynthetically derived sucrose stand out as key regulators of root architecture, guiding plants in their foraging efforts to maximize resource acquisition. However, the mechanisms by which plants integrate these signals to modulate root growth, particularly lateral root development, remain only partially understood. This study employs differential growth analysis to determine the degree of interplay between nitrate and sucrose sensing pathways mediating root growth, specifically refining the role for CEP (C-terminally Encoded Peptide) Receptor 1 (CEPR1). Pathways modulating root growth in response to perception of nitrate and sucrose do not operate independently and rely on CEPR1 to dynamically inhibit lateral root growth based on nitrate availability in a sucrose dependent manner. These findings highlight the interplay between distinct nutrient sensing pathways in adjusting plant root architecture and accentuate the sophisticated adaptive strategies plants employ in nutrient foraging.