This figure illustrates the methodological approach for measuring somitogenesis in a developing chick embryo. Panel A displays a time-lapse series of dark-field microscopy images from Hamburger-Hamilton stage 7 (HH7) to HH10, showing the anterior-posterior elongation and the progressive formation of somites as segmental paired blocks of paraxial mesoderm. Panel B is a schematic diagram illustrating the measurement of the Segmented Region (SEG), defined as the distance between the first and last formed somitic clefts across time points t1 to t3. Panel C is a line graph showing detrended SEG length in micrometers, where periodic peaks exceeding a 50 μm threshold identify the discrete addition of new somites. Panel D is a stepwise progression chart plotting total SEG length over time (minutes). Each color-coded horizontal step represents the formation of a specific somite (1 through 9), where vertical distance (L) indicates individual somite length and horizontal distance (T) indicates the time interval of formation. This visual content demonstrates developmental biology principles and quantitative morphometric analysis of embryonic segmentation.

Micrograph showing a cultured embryonic flank explant used in developmental biology research. The image is split into two panels: the top panel shows the original specimen, and the bottom panel provides detailed anatomical annotations. The translucent tissue sample is positioned on a filter over a metal support grid. Key structures identified include the forelimb (fl) and hindlimb (hl) buds, as well as the ventral and dorsal orientations. A series of somites are numbered from #12 to #24, illustrating the segmental organization of the paraxial mesoderm. An ellipse highlights a specific somite (#16), and a circle labeled 'B' marks the location of a grafted bead, likely used for local delivery of biochemical signals to study limb or somite development. This visual is representative of experimental embryology techniques used to analyze tissue patterning and organogenesis.

This scientific figure illustrates the oscillatory expression of the hairy1 gene during somitogenesis in early chick embryos. The image is divided into two panels: the top representing the 2-4 somite stage and the bottom representing the 6-7 somite stage. Each panel features a schematic representation of the experimental protocol and corresponding in situ hybridization results. The experimental setup demonstrates live-imaging where a newly formed somite cleft is identified at time t0; one side of the paraxial mesoderm is excised and fixed, while the contralateral side is cultured until the next somite (tf) forms. The right side of the figure displays microscopic photographs of the embryos after in situ hybridization for hairy1 mRNA (dark purple staining). High-intensity staining is visible within the segmented somites and the presomitic mesoderm. Asterisks and arrowheads indicate the sequential formation of somites, while brackets highlight consistent oscillatory expression domains between the t0 and tf stages. This visualization supports the biological concept that the segmentation clock is temporally coupled to physical somite formation along the anterior-posterior axis.

This composite educational graphic illustrates the cooperative effects of transcription factors Paraxis and Mef2d on dermomyotome formation in Xenopus embryos. Panels A-C show whole-mount in situ hybridization (WISH) and transverse sections tracking Paraxis and Mef2d mRNA expression from neurulation (stage 13) to tailbud stages. Notable findings include co-localization in the lateral paraxial mesoderm at stage 13, shifting to dorsolateral somite regions by stage 18. Panel D presents a Western blot confirming the knockdown efficiency of oligomorpholinos (moParaxis1) against Flag-tagged Paraxis protein. Panels E and F demonstrate the functional hierarchy through loss-of-function and gain-of-function experiments using Pax3 as a marker for dermomyotome development. Data show that moParaxis1 injection decreases Pax3 expression, which can be rescued by ParaxisF' mRNA. Conversely, overexpression of Paraxis (ParaxisGRF) or co-injection with Mef2dF significantly enhances and ventrally extends the Pax3 expression domain. Transverse sections reveal spatial orientation relative to the notochord (Nc). The visual supports the role of a Mef2d/Paraxis/Meox2/Pax3 regulatory pathway in early myogenesis and somite compartmentalization.

This composite image illustrates the experimental design and visual results of a developmental biology study using chick embryos to analyze somite differentiation. (A) Gross photograph of a chick embryo at HH stage 15–16, highlighting the newly formed somites targeted for electroporation. (B) Immunofluorescence microscopy of the somite region. PAX7 (green) labels the dermomyotome, HNK1 (blue) marks the neural crest, and MYF5 (red) indicates myotome formation. (C) An anatomical diagram providing a cross-sectional view of a single somite, categorizing the dorsomedial lip (DML, green), transition zone (blue), and nascent primary myotome (purple). (D) A diagnostic confocal microscopy image showing a maximum intensity projection of a somite 6 hours post-electroporation with Green Fluorescent Protein (GFP). The image reveals clustered, elongated green signals within a dashed white boundary, indicating successful mosaic expression of the construct in the target somitic cells. This visual set demonstrates the early stages of skeletal muscle progenitor formation and the spatial relationship between neural crest migration and myogenesis.

This composite educational image illustrates the molecular compartmentalization of somites in an N3-stage amphioxus (Branchiostoma) embryo, a key model for chordate evolution and developmental biology. Panel A provides a schematic of the cross-section, identifying the neural tube, notochord, and gut, with the somite divided into myotome (Myo), dorsolateral (Dl), centrolateral (Cl), and ventrolateral (Vl) domains. Panels B–D utilize double fluorescent in situ hybridization to demonstrate mutually exclusive expression of medial markers (mActin in red) and lateral markers (SPARC, Hand, and Zic in green). Panels E–R present a systematic survey of somite marker genes (e.g., MRF1/2, Pax3/7, Twist, FoxC, Pax1/9) across three imaging modalities: Differential Interference Contrast (DIC) for purple-stained gene expression, DIC + Hoechst, and Hoechst nuclear staining (fluorescence). Each row includes a localized diagram shaded in gray to indicate expression intensity. This comparative analysis demonstrates homologous patterning to vertebrate dermomyotome, myotome, and lateral plate mesoderm, while highlighting specific differences in sclerotome marker expression.

This composite educational graphic details rib cage development and skeletal defects in mouse embryos. Panel A provides a 3D perspective of the thoracic cage, while Panel B is a schematic defining the anatomy: the proximal/vertebral rib (bone, red) and distal/sternal rib (cartilage, blue). Panel C illustrates somite differentiation into dermatome, myotome, and sclerotome, highlighting Shh expression from the notochord. Panels D-G show E18.5 skeletal preparations using Alizarin red (bone) and Alcian blue (cartilage). Normal (D) and Apaf1 KO (E) embryos show 13 intact rib pairs and vertebrae. Shh KO (F) embryos display complete absence of vertebrae and proximal ribs, with mispatterned, discontinuous distal cartilaginous ribs. Shh;Apaf1 DKO (G) embryos exhibit the most severe phenotype, lacking both vertebrae and nearly all rib elements, leaving only the ossified sternum. Panels H-J provide stylized schematics summarizing these phenotypes. The visual highlights the essential role of Sonic Hedgehog signaling in sclerotome induction and the patterning of the proximal-distal axial skeleton.

This composite educational graphic details first-trimester embryonic development and yolk sac (YS) anatomy. Panel (a) is a 3D ultrasound of a 10-week-old embryo, showing the echogenic fetus and its connection to the secondary yolk sac via the vitelline duct, set against hypoechoic amniotic fluid. Panel (b) provides a corresponding anatomical diagram illustrating the spatial relationship between the amniotic cavity containing the fetus and the extraembryonic coelom (exocoelomic cavity) housing the yolk sac. It highlights key structures including the placenta, umbilical cord, uterine vessels, and uterine glands. Labels indicate physiological processes like nutrient secretion from uterine glands and membranous re-uptake by the yolk sac. Panel (c) is a high-magnification 2D ultrasound demonstrating the clinical method for measuring yolk sac size using two perpendicular outer-to-outer diameters. The image serves as a reference for early obstetric imaging, fetal-maternal nutrient exchange mechanisms, and standard sonographic biometry during the first trimester.

A series of four microphotographs (a-d) documenting the morphological development and organogenesis of a twelve-day-old rat embryo, used as a model for vertebrate embryology. Image (a) depicts the embryo within an intact yolk sac, highlighting the vitelline artery (VA) and vitelline vein (VV) which form the early yolk sac circulation. Images (b), (c), and (d) show the embryo with the yolk sac removed to reveal specific primordial structures. Key anatomical features identified include the telencephalon (TL), olfactory plate (OL), and forelimb bud (FL) in the anterior/cephalic region; the mesencephalon (ME), rhombencephalon (RE), optic primordia (OP), and otic structures (dorsal recess of otocyst, DR; otocyst, OC) in the mid-section; and the primitive heart chambers (atrium commune, AC; ventriculus communis, VC) and posterior somites (SO). The collection illustrates the cephalocaudal progression of development and is intended for educational study of musculoskeletal, neurological, and cardiovascular system initiation during the embryonic period.

This medical schematic illustrates the developmental stages of the human ovary and oogenesis, from embryonic migration to postnatal maturation. The timeline begins with primordial germ cells (PGCs) migrating from the yolk sac (e5-e7), influenced by Bmp signaling and undergoing mitosis. By e9.5, these cells colonize the gonadal primordium, followed by ovary specification (e10.5) involving key transcription factors and signaling molecules like Wnt4, FoxL2, Rspo1, and Sf1. The diagram highlights the formation of germ cell cysts through incomplete cytokinesis and the subsequent onset of meiosis at e14.5. Following cyst fragmentation, the development of primordial follicles is shown around e18.5, characterized by a single oocyte surrounded by pre-granulosa cells. The final stage depicted is postnatal follicle maturation (p3), showing the structural organization of an antral follicle with defined layers of granulosa cells and theca cells, situated near the ovarian epithelial cells. This illustration is an educational resource for embryology and reproductive biology.

This pathophysiology diagram illustrates the development and functional divergence of microglia in healthy versus neurodevelopmental disorder states. At the center, the 'Yolk sac derived precursors' represent the embryonic origin of these cells during central nervous system (CNS) colonization. Two developmental pathways are depicted. On the right, 'Developing Microglia' represent the healthy state, characterized by ramified morphology with long, thin processes. Their associated functions include CNS surveillance, synaptic pruning, neuronal survival regulation, and sensing of the tripartite synapse. On the left, 'Microglia in neurodevelopmental disorders' are shown with a more reactive morphology, featuring shorter, thicker, and more branched processes. This pathological state is associated with microglial proliferation, excessive cytokine production (IL-6, TNFα, IL-1β), altered TREM2 receptor expression, and dysfunctional synaptic pruning. Centrally listed receptors—including neurotransmitter, purinergic, chemokine, complement, and phagocytic receptors—underlie the sensory capabilities of both states. The diagram serves as an educational summary of how microglial dysfunction contributes to pathologies like Autism Spectrum Disorder (ASD) and Schizophrenia (SZ).

A historical anatomical plate comprising semi-schematic diagrams and illustrations of early human embryos, specifically the 'Gle' and 'v.H.' specimens, as documented by Graf v. Spee (1896). The layout includes profile views, median sections, and serial cross-sections organized to demonstrate early gestational development. Key features include the amnion (am), chorion (ch), and yolk sac/diencephalon (dh) structures. Figures I and II illustrate the 'Gle' embryo via semi-schematic median sections and profile views, highlighted with blue and red contrasting tones to show embryonic layers and blood vessel precursors. Figures III and 1-11 represent various sections of the 'v.H.' embryo, showing the morphology of the embryonic disc, allantois (al), and primitive streak area. The illustrations focus on the spatial relationships between the amniotic cavity, the embryonic body, and the surrounding extraembryonic membranes, providing foundational observations in human embryology and early morphogenesis.

This educational composite presents a macro photograph (A) and a corresponding schematic diagram (B) of a mammalian implantation site during the late limb bud stage of embryonic development. The median sagittal section illustrates the spatial relationship between the embryo (em) and maternal-fetal structures. Key anatomical landmarks include the embryo enclosed within the amnion (am) and visceral yolk sac (vys), the latter supplied by vitelline vessels (vv). The placental complex is situated on the mesometrial side (mes), consisting of a main placenta (mp) and a specialized subplacenta (sub) anchored to the basal decidua (bd). Opposing this, a prominent thick capsular decidua (cd) faces the antimesometrial wall (ant) of the uterus. The uterine cavity (uc) is visible as a distinct space lateral to the conceptus. The image serves to demonstrate the inverted yolk sac placental arrangement and the relative positioning of chorioallantoic and vitelline vascular systems in hystricomorph development. Labels also highlight umbilical vessels (uv) supplying the placental disk.

This composite educational graphic details the structure and development of the chick embryo chorioallantoic membrane (CAM), a common in vivo model for studying angiogenesis and inflammation. Panel A presents a schematic anatomical diagram of a 5-day-old embryo in ovo, labeling the shell, shell membrane, air sac, albumen, yolk, and amniotic cavity. A high-magnification cross-section illustrates the CAM's trilaminar structure: the allantoic epithelium (inner), the vascularized mesoderm, and the chorionic epithelium (outer, adjacent to the shell membrane). Panel B shows a clinical-style photograph of a 5-day-old chick embryo in ovo, demonstrating a dense radiating network of blood vessels consistent with early-stage angiography. Panel C provides a histological semithin section of a 12-day-old CAM, stained to highlight cellular morphology. The labels identify the allantoic epithelium (al), the thick stromal mesoderm (m) containing numerous cross-sections of blood vessels and capillaries, and the chorionic epithelium (ch). This content is relevant for researchers studying developmental biology, vascular pathologies, and wound healing models.

This composite educational graphic details first-trimester embryonic development and yolk sac (YS) anatomy. Panel (a) is a 3D ultrasound of a 10-week-old embryo, showing the echogenic fetus and its connection to the secondary yolk sac via the vitelline duct, set against hypoechoic amniotic fluid. Panel (b) provides a corresponding anatomical diagram illustrating the spatial relationship between the amniotic cavity containing the fetus and the extraembryonic coelom (exocoelomic cavity) housing the yolk sac. It highlights key structures including the placenta, umbilical cord, uterine vessels, and uterine glands. Labels indicate physiological processes like nutrient secretion from uterine glands and membranous re-uptake by the yolk sac. Panel (c) is a high-magnification 2D ultrasound demonstrating the clinical method for measuring yolk sac size using two perpendicular outer-to-outer diameters. The image serves as a reference for early obstetric imaging, fetal-maternal nutrient exchange mechanisms, and standard sonographic biometry during the first trimester.

This composite panel presents whole-mount in situ hybridization (WISH) images of mouse embryos at embryonic days E7.5–E7.75, comparing wild-type (Fam208a+/+) and Fam208aD6/D6 mutant phenotypes during gastrulation. The series evaluates several key developmental markers: Brachyury (A-A'), Cripto (B-B'), Noto (C-C'), Nodal (D-D'), Foxa2 (E-E'), and Shh (F-F'). Wild-type embryos demonstrate normal gastrulation progression, characterized by elongated primitive streaks (PS) and established nodes. In contrast, mutant embryos exhibit severe developmental arrest and gastrulation failure. Visual evidence shows a significantly shortened Brachyury-positive primitive streak and a delayed, truncated Cripto expression domain. Notably, markers of the organizer (node) and anterior mesendoderm—including Noto, Nodal, and Shh—are absent or severely reduced in the mutant distal epiblast. Foxa2 expression in mutants is restricted to the posterior region, failing to migrate anteriorly. These findings illustrate that loss of Fam208a leads to failed primitive streak elongation and defective specification of the anterior-posterior axis, with mutant embryos arrested at the Late Streak/Early Allantoic Bud (LSEB) stage while controls reach Late Head Fold (LHF) stages.

Educational developmental biology panel comparing wildtype and 'tyrn' (Pold1 hypomorph) mouse embryos at embryonic day E7.5. (A-D) Immunofluorescence (IF) images showing key gastrulation markers. Wildtype embryos display a well-extended primitive streak and organized anterior-posterior (A-P) axis, with Sox2 (red) marking the anterior neuroectoderm and Foxa2/T (Brachyury) labeling axial mesoderm and the primitive streak. In tyrn mutants, Sox2 is restricted to the distal tip, and T-staining reveals a significantly shortened primitive streak reaching only the posterior midpoint. (E-I) Whole-mount in situ hybridization (WISH) compares gene expression patterns. In mutants, Otx2 expression is shifted distally rather than anteriorly. Paraxial mesoderm marker Tbx6 is restricted to the posterior-proximal region in mutants, confirming defective primitive streak elongation. Twist and Tbx4 staining highlight a severe deficiency in extraembryonic mesoderm formation, particularly in the allantois, which is absent or drastically reduced in tyrn mutants. These visuals illustrate how impaired DNA synthesis due to Pold1 mutation disrupts cell proliferation, leading to failure in primitive streak extension and aberrant A-P axis orientation during mammalian gastrulation.

Educational developmental biology composite illustrating gene expression patterns during gastrulation in a stage 4 chicken embryo. Figure A: Schematic transverse section defining key morphological domains: lateral epiblast (green), preingression epiblast (pink), primitive streak (lavender), medial mesoderm (orange), and lateral mesoderm (purple). Panels B-O: Whole-mount in situ hybridization (ISH) images showing mRNA localization for 14 signaling molecules and receptors, including FGFR1-3, EPHA1, FGF4/8, PDGFRA, DLL1, SNAI2, T (Brachyury), WNT5B/8A, NOTCH1, and EFNB2. Panels B'-O': Corresponding transverse histological sections providing high-resolution visualization of spatial distribution across tissue layers. Distinctive staining patterns demonstrate differential expression: FGFR2/3 are localized to the lateral epiblast; EPHA1, FGF4/8, and DLL1 are concentrated in the preingression epiblast and primitive streak; while EFNB2 and WNT8A show broad expression in the mesoderm. This comparison illustrates the complex combinatorial gene regulation driving epithelial-to-mesenchymal transition (EMT) and mesodermal patterning during vertebrate development.

This diagnostic image set showcases laser scanning confocal microscopy of a mouse embryo at the mid-gastrulation stage (E7.5), utilizing a Hex-tdTomato reporter to track endoderm development. Panels A-D′ present whole-mount 3D renderings from lateral, anterior, posterior, and ventral perspectives. The Hex-tdTomato signal (red/white) is prominently localized to the midline (ml), the primitive streak (ps) region, and surrounding the node (n), while F-Actin (green) provides a general structural outline of the embryonic tissues. Panels E-F′ show transverse histological sections and high-magnification inserts (E′, F′) demonstrating the spatial relationship between the three primary germ layers. The Tomato reporter is specifically expressed within the outer endoderm (end) layer, including the definitive endoderm (arrowhead). The interior epiblast (epi) and developing mesoderm (mes) layers are largely devoid of the reporter signal. This visual resource is critical for understanding vertebrate embryology, specifically the genetic regulation of endodermal lineage specification and morphogenetic movements during gastrulation.