Developmental biology最新文献

Diverse organ shapes and sizes arise from the complex interplay between cellular properties, mechanical forces, and gene regulation. Drosophila wing- a flat structure and the globular haltere are two homologous flight appendages emerging from a similar group of progenitor cells. The activity of a single Hox transcription factor, Ultrabithorax (Ubx), governs the development of these two distinct organs- wing and haltere with different cell and organ morphologies. Our work reported here on differential development of wing and haltere suggest that the localisation and abundance of actomyosin complexes, apical cell contractility, properties of extracellular matrix, and cell size and shape, which is a result of various cell intrinsic and extrinsic forces, plausibly influence the flat vs. globular geometry of these two organs. Loss of Ubx function led to wing cell-like cellular features in haltere discs, and corresponding changes at the level of adult organs. We also observed that RNAi-mediated downregulation of Atrophin or Pten, in the background of downregulated Expanded (or elevated Yki), gave rise to varying degrees of wing-like homeotic transformations at the cellular as well as adult organ levels. Finally, we employ a minimal vertex model to demonstrate that the observed differences in tissue architecture are physically sufficient to maintain and elaborate early shape differences and mimic flat wing-like or globular haltere-like morphologies. Together, these findings show how genetic and mechanical factors are integrated to generate organ-specific morphologies and provide a framework for understanding the evolution of organ shape.

Alternative polyadenylation (APA) generates mRNA isoforms with distinct 3' UTR lengths, yet its role in mammalian preimplantation development remains largely unexplored. Here, we systematically delineated single-cell 3' UTR APA dynamics in human and mouse preimplantation embryos. The pronounced cell heterogeneity and developmental stage-specificity of APA patterns were uncovered. Zygotic genome activation (ZGA) genes predominantly utilized shortened 3' UTRs, indicating a potential role for 3' UTR shortening in ZGA. Integrative analyses with APAFlow and DAPAFlow revealed that N6-methyladenosine modification and its reader proteins coordinately regulate APA via APA-associated factors during ZGA. Moreover, the occurrence and expression of 3' UTR APA events are linked to miRNAs located adjacent to polyadenylation sites. Together, these findings delineate a dynamic 3' UTR APA landscape across mammalian preimplantation stages, highlighting its contribution to cellular heterogeneity and developmental regulation. Shortened 3' UTR APA may serve as a hallmark of ZGA, providing new insight into post-transcriptional regulation during preimplantation development.

Disruption of ALX1 causes frontonasal dysplasia syndrome-3, characterized by extreme microphthalmia, severe midfacial hypoplasia, and orofacial clefting. Recent studies have revealed critical tissue-specific roles of ALX1 in patterning both cranial mesoderm and cranial neural crest-derived facial mesenchyme. However, the molecular mechanisms regulating Alx1 gene expression during craniofacial development are largely unknown. In this study, we have identified a distal enhancer (Alx1-DE1) residing in a large intron of the neighboring Lrriq1 gene and demonstrate that deletion of this enhancer specifically affects Alx1 gene expression in the cranial neural crest-derived frontonasal mesenchyme and causes frontonasal and ocular defects partly phenocopying Alx1-deficient mice. We further functionally analyzed four evolutionary conserved regions, ECR1 - ECR4, in the Alx1-DE1 enhancer. Remarkably, ECR1, whose homologous region in the human genome harbors a lead single nucleotide variation significantly associated with facial and cranial vault shape differences, exhibits high enrichment of Twist1 transcription factor occupancy in mouse embryonic frontonasal tissues and drove Twist1-dependent reporter transgene expression specifically in the developing periocular and frontonasal mesenchyme in transgenic mice. These results reveal Alx1-DE1 as a crucial tissue-specific enhancer through which Twist1 and other major craniofacial developmental regulators control craniofacial patterning and morphogenesis.

Meibomian glands (MGs) in the eyelid secrete lipids that stabilize the tear film and protect the ocular surface. Abnormal MGs are associated with dry eye disease (DED), one of the most common ophthalmological disorders, but the molecular alterations underlying DED remain unclear. For most patients, DED is thought to be caused by the failure of MG-derived lipids to exit the gland due to hyperkeratinization-induced ductal obstruction; however, this theory has been difficult to test due to a lack of mouse models that recapitulate this phenotype. Here, we show that the MG central duct is lined by terminally differentiated cells that express Keratin 6, Keratin 79 and Abca12, a lipid transporter that promotes desquamation in the skin. Targeted genetic disruption of Abca12 in Keratin 6+ ductal cells causes a transient dry eye phenotype that is associated with severe hyperkeratosis and lipid retention specifically in the MG central duct. These findings demonstrate that constant desquamation is required to prevent MG ductal obstruction, and suggest that factors that modulate DED pathogenesis, including age, environment, inflammation and behavior, may converge on Abca12.

Enhancers are key regulatory elements that coordinate precise spatio-temporal gene expression during embryonic development. In this study, we used the chick to investigate the regulatory landscape of the highly conserved transcription factor DMRT1 which is essential for testes development. By performing ATAC-Seq and comparative genomics, we identified two putative enhancers, DMRT1 ROI14 and DMRT1 ROI8, located within intronic regions of DMRT1. To determine whether these two regions are active elements, we developed a Tol2 transposon-based enhancer reporter construct and established a gonad explant electroporation method. We show that while the HSV TK minimal promoter exhibits high levels of basal expression in the gonad, both DMRT1 ROI14 and DMRT1 ROI8 display enhancer activity in male explants only. Overall, this study is the first step towards deciphering the regulatory machinery behind the sex-specific expression of DMRT1.

Some developmental processes initiated in embryos or larvae persist into adulthood, a prominent example being maintenance of stem cells. To what extent are the mechanisms regulating these cell populations similar during different stages of life history? We have been studying how adult C. elegans hermaphrodites regulate the population of germline progenitor cells in response to the male pheromone ascr#10. Here we show that upon encountering ascr#10 adult hermaphrodites increase this cell population using mechanisms that are similar to but distinct from those previously revealed to be involved in the expansion of the germline in larvae. The core of the signaling axis in adults, as in larvae, consists of a neuronally-expressed TGFβ ligand DAF-7 and Notch-like LAG-2 signaling from the germline stem cell niche. An adult-specific serotonin signal acts upstream of DAF-7 to increase the population of germline progenitors, but only in actively egg-laying worms. Our results also suggest that during normal aging, declining expression of lag-2 and daf-7 contribute to germline senescence. Expression of these genes in aging hermaphrodites could be restored to youthful levels by ascr#10 or by pharmacological increase of serotonin signaling. We posit that neuronal signals regulate an environmentally appropriate rate of germline production in adults and argue that one driver of reproductive aging is the reduced expression of neuronal factors that regulate the germline.

Germ granules are ribonucleoprotein condensates that concentrate key maternal mRNAs needed for germ cell development. In Drosophila, nanos mRNA is selectively enriched in germ granules but the specific cis-acting elements mediating this process remain poorly defined. Here, we identify discrete sequence motifs in the nanos 3' UTR that regulate nanos enrichment specifically by promoting the growth of homotypic nanos mRNA clusters within granules, without affecting the initial targeting of nanos to germ granules. These sequence motifs are binding sites for the hnRNP M homolog Rumpelstiltskin (Rump) and mutation of Rump binding sites or Rump attenuates nanos homotypic cluster growth, reducing the amount of nanos inherited by germ cells. Consequently, germ cells exhibit defective migration to the gonad. Together, our findings reveal how small repeated sequence motifs and cognate RNA-binding proteins can tune enrichment of germ granule mRNAs by driving self-assembly into large RNA clusters. This strategy ensures sufficient inheritance of mRNAs to support germ cell development and may represent a general mechanism by which RNP condensates regulate transcript dosage.

Bioelectricity plays a key role in shaping tissues during early development. We previously demonstrated that elongating chicken feather buds establish a transient standing electrical current loop, with calcium channel-mediated inward current at the bud tip driving collective distal dermal cell movement that orients feather bud growth. Here, we evaluate the hypothesis that potassium channels carry the outward current at the bud base. We found potassium channel inhibition converts periodic feather primordia into horizontal stripes and alters bud aspect ratios by disrupting the bud elongation process. Bioelectric measurements show disruption of the entire current loop, affecting both outward current at the base and inward current at the feather bud tip. Hexagonally arrayed bud patterns become horizontal stripes and buds with irregular contours. In situ hybridization shows a thinner dermal condensation layer and failure to form distinct primordia. Despite disorganized morphology, dermal cells still express feather markers (NCAM, TnC, DKK1 and BMP4), and epidermis exhibits aberrant β-catenin, Shh, EDA and EDAR expression patterns. These findings show that potassium channel activity is required to couple cell fate specification with morphogenesis and highlight that ion channels are essential for cell-cell communication during periodic feather patterning and bud shaping.

Tissue homeostasis is dependent on precise coordination between endocrine organs in response to changes in organism physiology. Secreted circulating factors from adipocytes regulate the behavior of stem cell lineages in peripheral tissues in multiple organisms. In addition to their endocrine roles, Drosophila adipocytes store and secrete amino acid storage proteins throughout development. During the larval feeding period, adipocytes secrete storage proteins into the hemolymph, which are reabsorbed by the adipose tissue during metamorphosis to control adult organ size and fertility. Despite the known functions for storage proteins during the larval stages, their requirement during Drosophila adulthood and reproduction are uncharacterized. We discover that adipocyte-specific knockdown of the storage proteins Larval serum protein 1 (Lsp1) α/β/γ and Larval serum protein 2 (Lsp2) results in a decrease in germline stem cell (GSC) maintenance. We further reveal that decreased GSC number is due to downregulation of Target of Rapamycin (TOR) signaling in GSCs, suggesting compromised amino acid sensing directly in GSCs. We also find that the proteins that mediate storage protein adipocyte reabsorption, Fat body protein 1 (Fbp1) and Fat body protein 2 (Fbp2), are expressed in ovarian follicle cells. Intriguingly, Fbp1 nor Fbp2 appear to be required in follicle cells for GSC maintenance, suggesting undiscovered requirements for amino acid storage proteins in oogenesis. Our results highlight a novel role for Drosophila amino acid storage proteins during adulthood and in regulating tissue stem cell lineages.

In 1905, the American embryologist, Edwin Grant Conklin published three landmark papers that substantially influenced the fields of developmental biology and evolution. They described the development of ascidian embryos, focusing on cleavage patterns and cell lineages. They also followed the distribution of colored substances localized in the oocyte that are later segregated into specific cleavage-stage cells and ultimately into different organs. Conklin observed that the cleavage patterns were invariant between embryos and that the oocyte substances were consistently distributed to the same lineages that gave rise to distinct organs. Accordingly, the first two papers concluded that cell fate was largely determined by the organization of the oocyte cytoplasm, components of which were differentially distributed by invariant cleavage patterns. In the third paper, he tested this idea by damaging some cells and following the fate of the remaining ones; he observed that the surviving cells formed the regions and organs that they would have originally produced, leading him to conclude that the differentiated animal was a mosaic of cells predetermined by the contents of the oocyte cytoplasm they inherited. Conklin's observations and conclusions motivated over a century of research using progressively more sophisticated techniques to map cell lineages and to screen for localized molecules. We review some of those studies to show how they have led to our current understanding of the essential role played by maternally derived molecules. Of course, we now know that normal development results from a complex combination of processes beyond maternal determinants, including gene regulatory networks, cell-cell interactions, secreted factors, epigenetic and environmental influences. In addition, it is clear that different species utilize a mosaic distribution of maternal molecules to different extents. However, without Conklin's contributions, this vital component of developmental control might have been overlooked, and the subsequent identity of a variety of maternal determinants delayed.