The behavior and functions of embryonic microglia

Microglia are the resident immune cells of the central nervous system. Microglial progenitors are generated in the yolk sac during the early embryonic stage. Once microglia enter the brain primordium, these cells colonize the structure through migration and proliferation during brain development. Microglia account for a minor population among the total cells that constitute the developing cortex, but they can associate with many surrounding neural lineage cells by extending their filopodia and through their broad migration capacity. Of note, microglia change their distribution in a stage-dependent manner in the developing brain: microglia are homogenously distributed in the pallium in the early and late embryonic stages, whereas these cells are transiently absent from the cortical plate (CP) from embryonic day (E) 15 to E16 and colonize the ventricular zone (VZ), subventricular zone (SVZ), and intermediate zone (IZ). Previous studies have reported that microglia positioned in the VZ/SVZ/IZ play multiple roles in neural lineage cells, such as regulating neurogenesis, cell survival and neuronal circuit formation. In addition to microglial functions in the zones in which microglia are replenished, these cells indirectly contribute to the proper maturation of post-migratory neurons by exiting the CP during the mid-embryonic stage. Overall, microglial time-dependent distributional changes are necessary to provide particular functions that are required in specific regions. This review summarizes recent advances in the understanding of microglial colonization and multifaceted functions in the developing brain, especially focusing on the embryonic stage, and discuss the molecular mechanisms underlying microglial behaviors.

Immune System of Fish: An Evolutionary Perspective

Fishes are the most successful and diverse group of vertebrate animals, first appeared during Devonian period. Despite of certain differences, the immune system of fish is physiologically similar to that of higher vertebrates. The heterogenous group of fishes are the apparent link between innate immunity and the first appearance of the adaptive immune response. Importantly, fishes have immune organs homologous to that of mammalian immune system. In comparison to higher vertebrates, fishes live free in their environment from the early embryonic stage and during that time mostly they are dependent on non-specific immune system for their survival. In the fishes, non-specific immunity is the fundamental defense mechanism, therewith acquired immunity also plays key role in maintaining homeostasis by activation though a system of receptors proteins, which identify pathogen associated molecular pattern typical of pathogenic microorganism includes lipopolysaccharides, peptidoglycans, DNA, RNA and other molecules that are typically not present on the surface of multicellular organism. There are several external factors like environmental factors, biological factors, stress and internal factors like genetic makeup, age and sex, maternal effect etc. can affect immunological defense capabilities of the fishes.

Developmental Morphological Analyses on the Preglottal Salivary Gland in Japanese Quails (Coturnix Japonica)

To understand the development of the mucous preglottal salivary gland in Coturnix japonica (Japanese quail), morphological and histochemical studies were performed on 20 healthy Japanese quail embryos (aging from 10 th to 17 th incubation days) and 25 healthy quail chicks (aging from 0 th to 60 th days). The primordia of preglottal salivary gland was observed as an epithelial bud at the early embryonic stage, which then elongated and differentiated into secretory units by the end of this stage. In Japanese quails, the preglottal salivary gland was a mucous polystomatic tubulo-alveolar unpaired gland composed of two lateral portions and a middle one embedded into submucosa of the lingual root. The gland openings accompanied taste pore (8.17 μm) of taste buds associated salivary glands type; some skeletal muscle fibers embedded among secretory lobules extended from muscle cricohyoideus at 14 th day old quail chick. Also, both herbts corpuscles and secretory motor plexus could be detected among secretory lobules. Based on our investigations, the development of preglottal salivary gland could clearly be distinguished in the embryonic stage into prebud and bud stages at 10 th day old, cord and branching stages ended by cavitation at 11 th day old, canalization stage at 13 th day old, lobulation and secretory stages by the 17 th day old. This mucous secretion showed different histochemical reactions ended with highly alcinophilic mucous indicated highly sialomucin (acidic) content. Myoepithelial cells could be demonstrated at 17-day old quail embryo and there after, surrounded the secretory endpieces of the preglottal salivary gland.

Life-Long Neural Stem Cells Are Fate-Specified at an Early Developmental Stage

The origin and life-long fate of quiescent neural stem cells (NSCs) in the adult mammalian brain remain largely unknown. A few neural precursor cells in the embryonic brain elongate their cell cycle time and subsequently become quiescent postnatally, suggesting the possibility that life-long NSCs are selected at an early embryonic stage. Here, we utilized a GFP-expressing lentivirus to investigate the fate of progeny from individual lentivirus-infected NSCs by identifying the lentiviral integration site. Our data suggest that NSCs become specified to two or more lineages prior to embryonic day 13.5 in mice: one NSC lineage produces cells only for the cortex and another provides neurons to the olfactory bulb. The majority of neurosphere-forming NSCs in the adult brain are relatively dormant and generate very few cells, if any, in the olfactory bulb or cortex, and this NSC population could serve as a reservoir that is occasionally reactivated later in life.

Histochemical changes during development of Harderian gland in chicken

The present study was aimed to examine histochemical changes in the Harderian gland of pre and post hatched chicks from 11 day of incubation to 24 days of age. In pre hatched groups, the gland was in the developing stage. There was no well defined parenchyma, septa and capsule in early embryonic stage. Histochemical observation revealed that weak or negligible activity of PAS, AB/PAS and Sudan black B was seen in epithelial lining of Harderian gland on 18th and 20th day of incubation. The gland was compound tubule-acinar type at 20th day of incubation, consisted of capsule, parenchyma and stroma. PAS activity was seen in the capsule, septa, epithelial lining of acini and tubule and interstitial connective tissue cells. PAS activity was aggregated towards the apical part of the tubular epithelium as well as at the free luminal surface epithelium of the acini. PAS activity increases with the development of connective tissue component of Harderian gland with the advancement of age. The Harderian gland was predominantly mucus and lipid secreting gland. All epithelial cells of the glandular unit of Harderian gland contain both neutral and acidic mucin. Intense AB-positive activity was seen at the apex of tubule with the advancement of age. Sudan black B activity was recorded in the cytoplasm of epithelial lining of tubule and acini of the Harderian gland and their presence increases with age.

Iron deficiency affects early stages of embryonic hematopoiesis but not the endothelial to hematopoietic transition

Iron is an essential micronutrient for hematopoiesis and previous research suggested that iron deficiency in the pregnant female could cause anemia in the offspring. Since the development of all embryonic and adult blood cells begins in the embryo, we aimed to resolve the role of iron in embryonic hematopoiesis. For this purpose, we used an experimental system of mouse embryonic stem cells differentiation into embryonic hematopoietic progenitors. We modulated the iron status in cultures by adding either an iron chelator DFO for iron deficiency, or ferric ammonium citrate for iron excess, and followed the emergence of developing hematopoietic progenitors by flow cytometry. We found interestingly that iron deficiency by DFO did not block the endothelial to hematopoietic transition, the first step of hematopoiesis. However, it had a differential effect on the proliferation, survival and clonogenic capacity of hematopoietic progenitors. Surprisingly, iron deficiency affected erythro-myeloid Kitpos CD41+ progenitors significantly more than the primitive erythroid Kitneg CD41+. The Kitpos progenitors paradoxically died more, proliferated less and had more reduction in colony formation than Kitneg after 24 hours of DFO treatment. Kitpos progenitors expressed less transferrin-receptor on the cell surface and had less labile iron compared to Kitneg, which could reduce their capacity to compete for scarce iron and survive iron deficiency. We suggest that iron deficiency could disturb hematopoiesis already at an early embryonic stage by compromising survival, proliferation and differentiation of definitive hematopoietic progenitors.

A de novo EDA-variant in a litter of shorthaired standard Dachshunds with X-linked hypohidrotic ectodermal dysplasia

In this study, we present a detailed phenotype description and genetic elucidation of the first case of X-linked hypohidrotic ectodermal dysplasia in the shorthaired standard Dachshund. This condition is characterized by partial alopecia, missing and malformed teeth and a lack of eccrine sweat glands. Clinical signs including dental X-raying and histopathological findings were consistent with an ectodermal dysplasia. Pedigree analysis supported an X-recessive mode of inheritance. Whole-genome sequencing of one affected puppy and his dam identified a 1-basepair deletion within the ectodysplasin-A gene (CM000039.3:g.54509504delT, PRJEB27789). Sanger sequencing of further family members confirmed the PRJEB27789-variant. Validation in all available family members, 37 unrelated shorthaired standard Dachshunds, 128 Dachshunds from all other breeds and samples from 34 dog breeds revealed the PRJEB27789 variant to be private for this family. Two heterozygous females showed very mild alopecia but normal dentition. Since the dam is demonstrably the only heterozygous animal in the ancestry of the affected animals, we assume that the PRJEB27789-variant arose in the germline of the granddam or in an early embryonic stage of the dam. In conclusion, we detected a very recent de-novo EDA mutation causing X-linked hypohidrotic ectodermal dysplasia in the shorthaired standard Dachshund.

CpG islands’ clustering uncovers early development genes in the human genome

We address the problem of the annotation of CpG islands (CGIs) clusters in the human genome. Upon analyzing gene content within CGIs clusters, piRNA, tRNA, and miRNA-encoding genes were found as well as CpG-rich homeobox genes reported previously. Chromosome-wide CGI density is positively correlated with replication timing, confirming that CGIs may serve as open chromatin markers. Early embryonic stage expressed KRAB-ZNF genes abundant at chromosome 19 were found to be interlinked with CGI clusters. We detected that a number of long CGIs and CGI clusters are, in fact, tandem copies with multiple annotated macrosatellites and paralogous genes. This finding implies that tandem expansion of CGIs may serve as a substrate for nonhomologous recombination events.

Expression of a hindlimb-determining factor Pitx1 in the forelimb of the lizard Pogona vitticeps during morphogenesis

With over 9000 species, squamates, which include lizards and snakes, are the largest group of reptiles and second-largest order of vertebrates, spanning a vast array of appendicular skeletal morphology. As such, they provide a promising system for examining developmental and molecular processes underlying limb morphology. Using the central bearded dragon ( Pogona vitticeps ) as the primary study model, we examined limb morphometry throughout embryonic development and characterized the expression of three known developmental genes ( GHR, Pitx1 and Shh ) from early embryonic stage through to hatchling stage via reverse transcription quantitative polymerase chain reaction (RT-qPCR) and immunohistochemistry (IHC). In this study, all genes were found to be transcribed in both the forelimbs and hindlimbs of P. vitticeps. While the highest level of GHR expression occurred at the hatchling stage, Pitx1 and Shh expression was greatest earlier during embryogenesis, which coincides with the onset of the differentiation between forelimb and hindlimb length. We compared our finding of Pitx1 expression—a hindlimb-determining gene—in the forelimbs of P. vitticeps to that in a closely related Australian agamid lizard, Ctenophorus pictus , where we found Pitx1 expression to be more highly expressed in the hindlimb compared with the forelimb during early and late morphogenesis—a result consistent with that found across other tetrapods. Expression of Pitx1 in forelimbs has only rarely been documented, including via in situ hybridization in a chicken and a frog. Our findings from both RT-qPCR and IHC indicate that further research across a wider range of tetrapods is needed to more fully understand evolutionary variation in molecular processes underlying limb morphology.