Developmental Staging Research Articles

Minimum intervention oral care: staging and grading dental carious lesions in clinical practice

Developmental staging of carious lesions is pivotal for appropriate ethical clinical decision-making in contemporary caries management. Accurate assessment of lesion extent/severity (staging) and activity (grading) allows practitioners to provide the most appropriate preventive advice and suitable interventions, enabling the implementation of evidence-based, person-focused, prevention-based, team-delivered and susceptibility-related phased minimum intervention oral care. Minimally invasive dentistry remains an important operative interventive option for cavitated lesions, but intervening at the right stage ensures patients are not started on an irreversible, destructive restorative cycle unnecessarily. This article provides an update on recommended practical methods for staging the extent/severity and grading the activity of dental carious lesions, especially for those clinical teams delivering primary care and needing to navigate remuneration systems.

Sex and ancestry patterning of residual correlations in human dental development: Cooperative genetic interaction and phenotypic plasticity.

Most research in human dental age estimation has focused on point estimates of age, and most research on dental development theories has focused on morphology or eruption. Correlations between developing teeth using ordinal staging have received less attention. The effect of demographic variables on these correlations is unknown. I tested the effect of reference sample demographic variables on the residual correlation matrix using the lens of cooperative genetic interaction (CGI). The sample consisted of Moorrees et al., Journal of Dental Research, 1963, 42, 1490-1502, scores of left mandibular permanent teeth from panoramic radiographs of 880 London children 3-22.99 years of age stratified by year of age, sex, and Bangladeshi or European ancestry. A multivariate cumulative probit model was fit to each sex/ancestry group (n = 220), each sex or ancestry (n = 440), and all individuals (n = 880). Residual correlation matrices from nine reference sample configurations were compared using Bartlett's tests of between-sample difference matrices against the identity matrix, hierarchical cluster analysis, and dendrogram cophenetic correlations. Bartlett's test results were inconclusive. Cluster analysis showed clustering by tooth class, position within class, and developmental timing. Clustering patterns and dendrogram correlations showed similarity by sex but not ancestry. Expectations of CGI were supported for developmental staging. This supports using CGI as a model for explaining patterns of variation within the dentition. Sex was found to produce consistent patterns of dental correlations, whereas ancestry did not. Clustering by timing of development supports phenotypic plasticity in the dentition and suggests shared environment over genetic ancestry to explain population differences.

Clinical nurses’ compassion fatigue psychological experience process: a constructivist grounded theory study

BackgroundClinical nurses are susceptible to compassion fatigue when exposed to various types of traumatic events in patients for extended periods of time. However, the developmental process, staging, and psychological responses distinct to each stage of compassion fatigue in nurses are not fully clarified. This study aimed to explore the processes of compassion fatigue and the psychological experiences specific to each phase of compassion fatigue among clinical nurses.MethodsCharmaz’s Constructivist Grounded Theory methodology was used in this qualitative research. Semi-structured interviews were conducted with 13 clinical nurses with varying degrees of compassion fatigue from December 2020 to January 2021. Interview data were analyzed using grounded theory processes.ResultsThe data were categorized into five separate categories and 22 sub-categories. This study found that the process of compassion fatigue is dynamic and cumulative, which was classified into five phases: compassion experience period, compassion decrement period, compassion discomfort period, compassion distress period, and compassion fatigue period.ConclusionClinical nurses who experience compassion fatigue may go through five stages that are stage-specific and predictable. The findings can shed light on local and global applications to better understand the problem of nurses’ compassion fatigue. The interventions for addressing compassion fatigue in clinical nurses should be stage-specific, targeted, and individualized.

Using extended growth of cattle embryos in culture to gain insights into bovine developmental events on embryonic days 8 to 10

We have previously described an extended embryo culture system, based on uterine composition, growth factors and the cell culture additive B27, for growing cattle embryos in vitro beyond embryonic day 7. Here, extended in vitro embryos are compared to embryos developed in the uterus and are used to establish a developmental staging framework useful for understanding developmental events occurring until Day 10. Immunofluorescence or mRNA expression of the ICM/epiblast markers OCT4, SOX2 and NANOG, hypoblast markers GATA6, SOX17 and GATA4 and trophoblast genes CDX2, GATA3, ASCL2 and IFNT revealed the presence of four stages during this period that can be molecularly distinguished. These are expanded blastocyst, hatched blastocyst, hypoblast layering and early hypoblast migration. Interestingly NANOG and SOX17 show reciprocal expression at the expanded blastocyst stage, well before SOX2 and GATA6 expression refines to a similar so-called “salt and pepper” mutually exclusive expression in the ICM at the hatched blastocyst stage. GATA4 expression is only seen from stages when the hypoblast starts migrating around the blastocyst cavity. Intriguingly, trophoblast still expresses GATA6 and OCT4 in all cells during the expanded blastocyst phase, while SOX2 and SOX17 are seen in only some trophoblast cells. By the hypoblast-epiblast layering stage no trophoblast expression remains except for that of OCT4 protein, which starts waning in trophoblast once the hypoblast begins migrating. Lastly, it is shown that cultured embryos exhibit increased expression of the stress marker TP53 in the epiblast and hypoblast at late stages in comparison to embryos produced in the uterine environment.

Early ontogeny of the lesser sandeel (Ammodytes marinus).

Lesser sandeel (Ammodytes marinus) is widely distributed in North Sea ecosystems. Sandeel acts as a critical trophic link between zooplankton and top predators (fish, mammals, sea birds). Because they live buried in the sand, sandeel may be directly affected by the rapid expansion of anthropogenic activities linked to their habitat on the sea bottom (e.g., hydrocarbon extraction, offshore renewable energy, and subsea mining). It is, therefore, important to understand the impact of cumulative environmental and anthropogenic stressors on this species. A detailed description of the ontogenetic timeline and developmental staging for this species is lacking limiting the possibilities for comparative developmental studies assessing, e.g., the impact of various environmental stressors. A detailed description of the morphological development of lesser sandeel and their developmental trajectory, obtained through visual observations and microscopic techniques, is presented. Methods for gamete stripping and intensive culture of the early life stages are also provided. This work provides a basis for future research to understand the effect of cumulative environmental and anthropogenic stressors on development in the early life stages of lesser sandeel.

Future research directions of the model marine tubeworm Hydroides elegans and synthesis of developmental staging of the complete life cycle.

The biofouling marine tube worm, Hydroides elegans, is an indirect developing polychaete with significance as a model organism for questions in developmental biology and the evolution of host-microbe interactions. However, a complete description of the life cycle from fertilization through sexual maturity remains scattered in the literature, and lacks standardization. Here, we present a unified staging scheme synthesizing the major morphological changes that occur during the entire life cycle of the animal. These data represent a complete record of the life cycle, and serve as a foundation for connecting molecular changes with morphology. The present synthesis and associated staging scheme are especially timely as this system gains traction within research communities. Characterizing the Hydroides life cycle is essential for investigating the molecular mechanisms that drive major developmental transitions, like metamorphosis, in response to bacteria.

Attributes of communication aids as described by those supporting children and young people with AAC.

Those supporting children and young people who use augmentative and alternative communication (AAC) contribute to ongoing complex decision-making about communication aid selection and support. Little is known about how these decisions are made in practice and how attributes of the communication aid are described or considered. To understand how communication aid attributes were described by those involved in AAC recommendations and support for children and young people, and how these attributes were described as impacting on AAC use. A secondary qualitative analysis was completed of interview and focus group data from 91 participants involved in the support of 22 children and young people. Attributes of communication aids described by participants were extracted as themes and this paper reports a descriptive summary of the identified software (non-hardware) attributes. Decisions were described in terms of comparisons between commercially available pre-existing vocabulary packages. Attributes related to vocabulary, graphic representation, consistency and intuitiveness of design, and ease of editing were identified. Developmental staging of vocabularies, core and fringe vocabulary, and vocabulary personalization were attributes that were described as being explicitly considered in decisions. The potential impact of graphic symbol choice did not seem to be considered strongly. The physical and social environment was described as the predominant factor driving the choice of a number of attributes. Specific attributes that appear to be established in decision-making in these data have limited empirical research literature. Terms used in the literature to describe communication aid attributes were not observed in these data. Practice-based evidence does not appear to be supported by the available research literature and these findings highlight several areas where empirical research is needed in order to provide a robust basis for practice. What is already known on the subject Communication aid attributes are viewed as a key consideration by practitioners and family members in AAC decision-making; however, there are few empirical studies investigating language and communication attributes of communication aids. It is important to understand how those involved in AAC recommendations and support view communication aid attributes and the impact different attributes have. What this paper adds to existing knowledge This study provides a picture of how communication aids are described by practitioners and family members involved in AAC support of children and young people. A range of attributes is identified from the analysis of these qualitative data as well as information about how participants perceive these attributes as informing decisions. What are the potential or actual clinical implications of this work? This study provides a basis on which practitioners and others involved in AAC support for children and young people can review and reflect on their own practice and so improve the outcomes of AAC decisions. The study provides a list of attributes that appear to be considered in practice and so also provides a resource for researchers looking to ensure there is a strong empirical basis for AAC decisions.

Developmental Staging of Sexual Egg Formation in Daphnia pulex: Unmated Females Resorb Meiotic Oocytes to Resist Starvation.

Under favorable conditions, daphnids produce only female neonates by parthenogenesis, while they produce male neonates and start sexual reproduction when they detect cues signaling a deteriorating environment. Identifying the regulatory mechanisms of such cyclical parthenogenesis is important for understanding how organisms adapt to environments and expand their habitats. However, most previous studies using the model species Daphnia magna and Daphnia pulex have focused on production of male offspring (sex determination), whereas the process of meiosis induction in females has not been investigated. Here, we report a simple experimental method to induce meiosis effectively in D. pulex females. Through observations using the new method, we describe the process of sexual reproduction along an individual developmental time course. Meiotic oocytes are oviposited only when females mate within a certain time window, and failure to mate within that window results in subsequent resorption of oocytes, a measure that may increase resistance to starvation. These results further our understanding of regulatory mechanisms and evolutionary processes in the complicated life-history of Daphnia.

Phenotypic study for embryonic and larval development of common carp (Cyprinus carpio L., 1758)

The early development of common carp (Cyprinus carpio L., 1758) was studied from fertilizing until juvenile stage. The series developmental staging was done using morphological characteristics. Results identified eight main periods of embryogenesis: zygote, morula, blastula, gastrula, neurella, segmentation, pharyngula and hatching period. Results also identified and described nine larval development stages: hatching larva stage, rudimentary - pectoral fin and gill arch stage, melanoid-eye with gas bladder emergence stage, one chamber gas bladder with yolk absorption stage, two chamber gas bladder stage, pelvic fin bud with dorsal fin formation stage, anal-caudal and pelvic fin formation stage, squamation stage and juvenile stage. Hatching occurred at 38h after egg fertilization. The fertilized egg was spherical, yellowish, transparent and 2.5 mm in diameter. The transition from larva to juvenile occurred in 30 days.

Murine Neural Plate Targeting by In Utero Nano-Injection (NEPTUNE) at Embryonic Day 7.5

Manipulating gene expression in the developing mouse brain in utero holds great potential for functional genetics studies. However, it has previously largely been restricted to the manipulation of embryonic stages post-neurulation. A protocol was developed to inject the amniotic cavity at embryonic day (E)7.5 and deliver lentivirus, encoding cDNA or shRNA, targeting >95% of the neural plate and neural crest cells, contributing to the future brain, spinal cord, and peripheral nervous system. This protocol describes the steps necessary to achieve successful transduction, including grinding of the glass capillary needles, pregnancy verification, developmental staging using ultrasound imaging, and optimal injection volumes matched to embryonic stages. Following this protocol, it is possible to achieve transduction of >95% of the developing brain with high-titer lentivirus and thus perform whole-brain genetic manipulation. In contrast, it is possible to achieve mosaic transduction using lower viral titers, allowing for genetic screening or lineage tracing. Injection at E7.5 also targets ectoderm and neural crest contributing to distinct compartments of the eye, tongue, and peripheral nervous system. This technique thus offers the possibility to manipulate gene expression in mouse neural-plate- and ectoderm-derived tissues from preneurulation stages, with the benefit of reducing the number of mice used in experiments.

Murine Neural Plate Targeting by In Utero Nano-Injection (NEPTUNE) at Embryonic Day 7.5.

Manipulating gene expression in the developing mouse brain in utero holds great potential for functional genetics studies. However, it has previously largely been restricted to the manipulation of embryonic stages post-neurulation. A protocol was developed to inject the amniotic cavity at embryonic day (E)7.5 and deliver lentivirus, encoding cDNA or shRNA, targeting >95% of the neural plate and neural crest cells, contributing to the future brain, spinal cord, and peripheral nervous system. This protocol describes the steps necessary to achieve successful transduction, including grinding of the glass capillary needles, pregnancy verification, developmental staging using ultrasound imaging, and optimal injection volumes matched to embryonic stages. Following this protocol, it is possible to achieve transduction of >95% of the developing brain with high-titer lentivirus and thus perform whole-brain genetic manipulation. In contrast, it is possible to achieve mosaic transduction using lower viral titers, allowing for genetic screening or lineage tracing. Injection at E7.5 also targets ectoderm and neural crest contributing to distinct compartments of the eye, tongue, and peripheral nervous system. This technique thus offers the possibility to manipulate gene expression in mouse neural-plate- and ectoderm-derived tissues from preneurulation stages, with the benefit of reducing the number of mice used in experiments.

Origin, molecular specification, and stemness of astrocytes.

Astrocytes are the most abundant cell type in the central nervous system, carrying out a wide spectrum of biological functions. During early development, neural progenitor cells in the ventricular zone first produce neurons, followed by macroglia in the form of astrocytes or oligodendrocytes. Although the lineage progression of oligodendrocytes has been well understood, the developmental staging of astrocytes has not been defined and the molecular mechanisms underlying their fate specification and differentiation remain largely unknown. The recent advent of sophisticated molecular biology technology, especially single-cell sequencing, has enabled a deeper understanding of the patterning and molecular specification of astrocyte lineage. Based on the recent single-cell sequencing data, we provide an up-to-date and mechanistic review of the early development and heterogeneity of astrocyte lineage in the developing cortex, and compile a list of stage-specific markers for astrocyte development. In addition, emerging evidence suggests that under physiological conditions, mature astrocytes are partially specialized progenitor cells that have functionally adapted to local neuronal microenvironment. Under pathological or injury conditions, astrocytes are capable of reentering cell cycles and differentiating into other neural cell types under the influence of both intrinsic factors and environmental cues.

Developmental deficits and staging of dynamics of age associated Alzheimer\u2019s disease neurodegeneration and neuronal loss in subjects with Down syndrome

The increased life expectancy of individuals with Down syndrome (DS) is associated with increased prevalence of trisomy 21–linked early-onset Alzheimer’s disease (EOAD) and dementia. The aims of this study of 14 brain regions including the entorhinal cortex, hippocampus, basal ganglia, and cerebellum in 33 adults with DS 26–72 years of age were to identify the magnitude of brain region–specific developmental neuronal deficits contributing to intellectual deficits, to apply this baseline to identification of the topography and magnitude of neurodegeneration and neuronal and volume losses caused by EOAD, and to establish age-based staging of the pattern of genetically driven neuropathology in DS. Both DS subject age and stage of dementia, themselves very strongly correlated, were strong predictors of an AD-associated decrease of the number of neurons, considered a major contributor to dementia. The DS cohort was subclassified by age as pre-AD stage, with 26–41-year-old subjects with a full spectrum of developmental deficit but with very limited incipient AD pathology, and 43–49, 51–59, and 61–72-year-old groups with predominant prevalence of mild, moderately severe, and severe dementia respectively. This multiregional study revealed a 28.1% developmental neuronal deficit in DS subjects 26–41 years of age and 11.9% AD-associated neuronal loss in DS subjects 43–49 years of age; a 28.0% maximum neuronal loss at 51–59 years of age; and a 11.0% minimum neuronal loss at 61–72 years of age. A total developmental neuronal deficit of 40.8 million neurons and AD-associated neuronal loss of 41.6 million neurons reflect a comparable magnitude of developmental neuronal deficit contributing to intellectual deficits, and AD-associated neuronal loss contributing to dementia. This highly predictable pattern of pathology indicates that successful treatment of DS subjects in the fourth decade of life may prevent AD pathology and functional decline.

Integration of embryo–endosperm interaction into a holistic and dynamic picture of seed development using a rice mutant with notched-belly kernels

Interaction between the embryo and endosperm affects seed development, an essential process in yield formation in crops such as rice. Signals that mediate communication between embryo and endosperm are largely unknown. We used the notched-belly (NB) mutant with impaired communication between embryo and endosperm to investigate the effect of the embryo on developmental staging of the endosperm and signaling pathways in the embryo that regulate endosperm development. Hierachical clustering of mRNA datasets from embryo and endosperm samples collected during development in NB and a wild type showed a delaying effect of the embryo on the developmental transition of the endosperm by extension of the middle stage. K-means clustering further identified coexpression modules of gene sets specific to embryo and endosperm development. Combined gene expression and biochemical analysis showed that T6P–SnRK1, gibberellin and auxin signaling by the embryo regulate endosperm developmental transition. We propose a new seed developmental staging system for rice and identify the most detailed signature of rice grain formation to date. These will direct genetic strategies for rice yield improvement.

Nutritional Formulation for Patients with Angelman Syndrome: A Randomized, Double-Blind, Placebo-Controlled Study of Exogenous Ketones

BackgroundAngelman syndrome (AS) patients often respond to low glycemic index therapy to manage refractory seizures. These diets significantly affect quality of life and are challenging to implement. These formulations may have benefits in AS even in the absence of biomarkers suggesting ketosis. ObjectivesWe aimed to compare an exogenous medical food ketone formulation (KF) with placebo for the dietary management of AS. MethodsThis randomized, double-blind, placebo-controlled, crossover clinical trial was conducted in an academic center from 15 November, 2018 to 6 January, 2020. Thirteen participants with molecularly confirmed AS aged 4–11 y met the criteria and completed the 16-wk study. The study consisted of four 4-wk phases: a baseline phase, a blinded KF or placebo phase, a washout phase, and the crossover phase with alternate blinded KF or placebo. Primary outcomes were safety and tolerability rated by retention in the study and adherence to the formulation. Additional secondary outcomes of safety in this nonverbal population included blood chemistry, gastrointestinal health, seizure burden, cortical irritability, cognition, mobility, sleep, and developmental staging. ResultsData were compared between the baseline, KF, and placebo epochs. One participant exited the trial owing to difficulty consuming the formulation. Adverse events included an increase in cholesterol in 1 subject when consuming KF and a decrease in albumin in 1 subject when consuming placebo. Stool consistency improved with KF consumption, from 6.04 ± 1.61 at baseline and 6.35 ± 1.55 during placebo to 4.54 ± 1.19 during KF (P = 0.0027). Electroencephalograph trends showed a decrease in Δ frequency power during the KF arm and event-related potentials suggested a change in the frontal memory response. Vineland-3 showed improved fine motor skills in the KF arm. ConclusionsThe exogenous KF appears safe. More data are needed to determine the utility of exogenous ketones as a nutritional approach in children with AS. This trial was registered at clinicaltrials.gov as NCT03644693.

Embryonic development in the acoel Hofstenia miamia.

Acoels are marine worms that belong to the phylum Xenacoelomorpha, a deep-diverging bilaterian lineage. This makes acoels an attractive system for studying the evolution of major bilaterian traits. Thus far, acoel development has not been described in detail at the morphological and transcriptomic levels in a species in which functional genetic studies are possible. We present a set of developmental landmarks for embryogenesis in the highly regenerative acoel Hofstenia miamia. We generated a developmental staging atlas from zygote to hatched worm based on gross morphology, with accompanying bulk transcriptome data. Hofstenia embryos undergo a stereotyped cleavage program known as duet cleavage, which results in two large vegetal pole 'macromeres' and numerous small animal pole 'micromeres'. These macromeres become internalized as micromere progeny proliferate and move vegetally. We also noted a second, previously undescribed, cell-internalization event at the animal pole, following which we detected major body axes and tissues corresponding to all three germ layers. Our work on Hofstenia embryos provides a resource for mechanistic investigations of acoel development, which will yield insights into the evolution of bilaterian development and regeneration.

Variation in Ontogenetic Facial Suture Fusion Patterns in Catarrhines

Timing of craniofacial suture fusion is important for the determination of demographics and primate ontogeny. There has been much work concerning the timing of fusion of calvarial sutures over the last century, but little comprehensive work focusing on facial sutures. Here we assess the relationships of facial suture fusion across ontogeny among select catarrhines. Fusion timing patterns for 5 facial sutures were examined in 1,599 crania of Homo, Pan, Gorilla, Pongo, Hylobatidae, Papio, and Macaca. Calvarial volume (early ontogeny) and dental eruption (late ontogeny) were used as indicators of stage of development. General linear models, test for homogeneity of slopes, and ANOVA were used to determine differences in timing of fusion by taxon. For calvarial volume, taxonomic groups segregated by regression slopes, with models for Homo indicating sutural fusion throughout ontogeny, Pongo, Macaca, and Papio representing earlier and more complete suture fusion, and Pan, Gorilla, and Hylobatidae indicating very early facial suture fusion. Similar patterns are observed when dental eruption is used for developmental staging. Only Gorilla and Hylobatidae are observed to, generally, fuse all facial suture sites in adulthood. Finally, Homo appears to be unique in its delay and patency of sutures into late ontogeny. The taxonomic patterns of facial suture closure identified in this study likely reflect important evolutionary shifts in facial growth and development in catarrhines.

An Updated Staging System for Cephalochordate Development: One Table Suits Them All.

Chordates are divided into three subphyla: Vertebrata, Tunicata, and Cephalochordata. Phylogenetically, the Cephalochordata, more commonly known as lancelets or amphioxus, constitute the sister group of Vertebrata and Tunicata. Lancelets are small, benthic, marine filter feeders, and their roughly three dozen described species are divided into three genera: Branchiostoma, Epigonichthys, and Asymmetron. Due to their phylogenetic position and their stereotypical chordate morphology and genome architecture, lancelets are key models for understanding the evolutionary history of chordates. Lancelets have thus been studied by generations of scientists, with the first descriptions of adult anatomy and developmental morphology dating back to the 19th century. Today, several different lancelet species are used as laboratory models, predominantly for developmental, molecular and genomic studies. Surprisingly, however, a universal staging system and an unambiguous nomenclature for developing lancelets have not yet been adopted by the scientific community. In this work, we characterized the development of the European lancelet (Branchiostoma lanceolatum) using confocal microscopy and compiled a streamlined developmental staging system, from fertilization through larval life, including an unambiguous stage nomenclature. By tracing growth curves of the European lancelet reared at different temperatures, we were able to show that our staging system permitted an easy conversion of any developmental time into a specific stage name. Furthermore, comparisons of embryos and larvae from the European lancelet (B. lanceolatum), the Florida lancelet (Branchiostoma floridae), two Asian lancelets (Branchiostoma belcheri and Branchiostoma japonicum), and the Bahamas lancelet (Asymmetron lucayanum) demonstrated that our staging system could readily be applied to other lancelet species. Although the detailed staging description was carried out on developing B. lanceolatum, the comparisons with other lancelet species thus strongly suggested that both staging and nomenclature are applicable to all extant lancelets. We conclude that this description of embryonic and larval development will be of great use for the scientific community and that it should be adopted as the new standard for defining and naming developing lancelets. More generally, we anticipate that this work will facilitate future studies comparing representatives from different chordate lineages.

Comprehensive comparative morphology and developmental staging of final instar larvae toward metamorphosis in the insect order Odonata

The order Odonata (dragonflies and damselflies) is among the most ancestral groups of winged insects with drastic morphological changes upon metamorphosis, and thus important for understanding evo-devo aspects of insects. However, basic developmental descriptions of Odonata have been scarce. In an attempt to establish the foundation of developmental and experimental biology of Odonata, we present an unprecedentedly comprehensive survey of dragonflies and damselflies, in total 158 larvae representing 49 species and 14 families, wherein morphological changes of all the final and/or penultimate instar larvae were photographed and monitored everyday. Although their morphology and development were diverse, we consistently identified two visually recognizable morphogenetic events in the final larval instar, namely start of wing expansion and onset of melanization on the wing sheaths, thereby categorizing the final instar into three stages. While the duration of the first stage ranged 4–66 days across diverse Odonata species, the second or third stages exhibited relatively small variation ranging 3–22 days or 1–8 days, respectively, probably reflecting the steady and irreversible metamorphosis process after stage 2. We also described other characteristic morphological changes during the larval development, although they were observed only in some Odonata species and lineages.

2004 – DECIPHERING HUMAN MACROPHAGE DEVELOPMENT AT SINGLE-CELL RESOLUTION

Macrophages are the first cells of the nascent immune system to emerge during embryonic development. In mice, embryonic macrophages infiltrate developing organs, where they differentiate symbiotically into tissue-resident macrophages (TRMs). However, our understanding of the origins and specialization of macrophages in human embryos is limited. Here we isolated CD45+ haematopoietic cells from human embryos at Carnegie stages 11 to 23 and subjected them to transcriptomic profiling by single-cell RNA sequencing, followed by functional characterization of a population of CD45+CD34+CD44+ yolk sac-derived myeloid-biased progenitors (YSMPs) by single-cell culture. We also mapped macrophage heterogeneity across multiple anatomical sites and identified diverse subsets, including various types of embryonic TRM (in the head, liver, lung and skin). We further traced the specification trajectories of TRMs from either yolk sac-derived primitive macrophages or YSMP-derived embryonic liver monocytes using both transcriptomic and developmental staging information, with a focus on microglia. Finally, we evaluated the molecular similarities between embryonic TRMs and their adult counterparts. Our data represent a comprehensive characterization of the spatiotemporal dynamics of early macrophage development during human embryogenesis, providing a reference for future studies of the development and function of human TRMs.