Subscribe: Development RESEARCH ARTICLES
Preview: Development RESEARCH ARTICLES


Development - recent RESEARCH ARTICLES articles


Hoxc8 initiates an ectopic mammary program by regulating Fgf10 and Tbx3 expression and Wnt/{beta}-catenin signaling [RESEARCH ARTICLES]


Lara S. Carroll and Mario R. Capecchi

The role of Hox genes in the formation of cutaneous accessory organs such as hair follicles and mammary glands has proved elusive, a likely consequence of overlapping function and expression among various homeobox factors. Lineage and immunohistochemical analysis of Hoxc8 in mice revealed that this midthoracic Hox gene has transient but strong regional expression in ventrolateral surface ectoderm at E10.5, much earlier than previously reported. Targeted mice were generated to conditionally misexpress Hoxc8 from the Rosa locus using select Cre drivers, which significantly expanded the domain of thoracic identity in mutant embryos. Accompanying this expansion was the induction of paired zones of ectopic mammary development in the cervical region, which generated between three and five pairs of mammary placodes anterior to the first wild-type mammary rudiment. These rudiments expressed the mammary placode markers Wnt10b and Tbx3 and were labeled by antibodies to the mammary mesenchyme markers ERα and androgen receptor. Somitic Fgf10 expression, which is required for normal mammary line formation, was upregulated in mutant cervical somites, and conditional ablation of ectodermal Tbx3 expression eliminated all normally positioned and ectopic mammary placodes. We present evidence that Hoxc8 participates in regulating the initiation stages of mammary placode morphogenesis, and suggest that this and other Hox genes are likely to have important roles during regional specification and initiation of these and other cutaneous accessory organs.

The NIMA-like kinase Nek2 is a key switch balancing cilia biogenesis and resorption in the development of left-right asymmetry [RESEARCH ARTICLES]


S. Joseph Endicott, Basudha Basu, Mustafa Khokha, and Martina Brueckner

Vertebrate left-right (LR) asymmetry originates at a transient left-right organizer (LRO), a ciliated structure where cilia play a crucial role in breaking symmetry. However, much remains unknown about the choreography of cilia biogenesis and resorption at this organ. We recently identified a mutation affecting NEK2, a member of the NIMA-like serine-threonine kinase family, in a patient with congenital heart disease associated with abnormal LR development. Here, we report how Nek2 acts through cilia to influence LR patterning. Both overexpression and knockdown of nek2 in Xenopus result in abnormal LR development and reduction of LRO cilia count and motility, phenotypes that are modified by interaction with the Hippo signaling pathway. nek2 knockdown leads to a centriole defect at the LRO, consistent with the known role of Nek2 in centriole separation. Nek2 overexpression results in premature ciliary resorption in cultured cells dependent on function of the tubulin deacetylase Hdac6. Finally, we provide evidence that the known interaction between Nek2 and Nup98, a nucleoporin that localizes to the ciliary base, is important for regulating cilium resorption. Together, these data show that Nek2 is a switch balancing ciliogenesis and resorption in the development of LR asymmetry.

Cardiac contraction activates endocardial Notch signaling to modulate chamber maturation in zebrafish [RESEARCH ARTICLES]


Leigh Ann Samsa, Chris Givens, Eleni Tzima, Didier Y. R. Stainier, Li Qian, and Jiandong Liu

Congenital heart disease often features structural abnormalities that emerge during development. Accumulating evidence indicates a crucial role for cardiac contraction and the resulting fluid forces in shaping the heart, yet the molecular basis of this function is largely unknown. Using the zebrafish as a model of early heart development, we investigated the role of cardiac contraction in chamber maturation, focusing on the formation of muscular protrusions called trabeculae. By genetic and pharmacological ablation of cardiac contraction, we showed that cardiac contraction is required for trabeculation through its role in regulating notch1b transcription in the ventricular endocardium. We also showed that Notch1 activation induces expression of ephrin b2a (efnb2a) and neuregulin 1 (nrg1) in the endocardium to promote trabeculation and that forced Notch activation in the absence of cardiac contraction rescues efnb2a and nrg1 expression. Using in vitro and in vivo systems, we showed that primary cilia are important mediators of fluid flow to stimulate Notch expression. Together, our findings describe an essential role for cardiac contraction-responsive transcriptional changes in endocardial cells to regulate cardiac chamber maturation.

Brg1 coordinates multiple processes during retinogenesis and is a tumor suppressor in retinoblastoma [RESEARCH ARTICLES]


Issam Aldiri, Itsuki Ajioka, Beisi Xu, Jiakun Zhang, Xiang Chen, Claudia Benavente, David Finkelstein, Dianna Johnson, Jennifer Akiyama, Len A. Pennacchio, and Michael A. Dyer

Retinal development requires precise temporal and spatial coordination of cell cycle exit, cell fate specification, cell migration and differentiation. When this process is disrupted, retinoblastoma, a developmental tumor of the retina, can form. Epigenetic modulators are central to precisely coordinating developmental events, and many epigenetic processes have been implicated in cancer. Studying epigenetic mechanisms in development is challenging because they often regulate multiple cellular processes; therefore, elucidating the primary molecular mechanisms involved can be difficult. Here we explore the role of Brg1 (Smarca4) in retinal development and retinoblastoma in mice using molecular and cellular approaches. Brg1 was found to regulate retinal size by controlling cell cycle length, cell cycle exit and cell survival during development. Brg1 was not required for cell fate specification but was required for photoreceptor differentiation and cell adhesion/polarity programs that contribute to proper retinal lamination during development. The combination of defective cell differentiation and lamination led to retinal degeneration in Brg1-deficient retinae. Despite the hypocellularity, premature cell cycle exit, increased cell death and extended cell cycle length, retinal progenitor cells persisted in Brg1-deficient retinae, making them more susceptible to retinoblastoma. ChIP-Seq analysis suggests that Brg1 might regulate gene expression through multiple mechanisms.

Src64 controls a novel actin network required for proper ring canal formation in the Drosophila male germline [RESEARCH ARTICLES]


Asmund Husabo Eikenes, Lene Malerod, Anette Lie-Jensen, Catherine Sem Wegner, Andreas Brech, Knut Liestol, Harald Stenmark, and Kaisa Haglund

In many organisms, germ cells develop as cysts in which cells are interconnected via ring canals (RCs) as a result of incomplete cytokinesis. However, the molecular mechanisms of incomplete cytokinesis remain poorly understood. Here, we address the role of tyrosine phosphorylation of RCs in the Drosophila male germline. We uncover a hierarchy of tyrosine phosphorylation within germline cysts that positively correlates with RC age. The kinase Src64 is responsible for mediating RC tyrosine phosphorylation, and loss of Src64 causes a reduction in RC diameter within germline cysts. Mechanistically, we show that Src64 controls an actin network around the RCs that depends on Abl and the Rac/SCAR/Arp2/3 pathway. The actin network around RCs is required for correct RC diameter in cysts of developing germ cells. We also identify that Src64 is required for proper germ cell differentiation in the Drosophila male germline independent of its role in RC regulation. In summary, we report that Src64 controls actin dynamics to mediate proper RC formation during incomplete cytokinesis during germline cyst development in vivo.

A zinc finger protein that regulates oligodendrocyte specification, migration and myelination in zebrafish [RESEARCH ARTICLES]


Harwin Sidik and William S. Talbot

Precise control of oligodendrocyte migration and development is crucial for myelination of axons in the central nervous system (CNS), but important questions remain unanswered about the mechanisms controlling these processes. In a zebrafish screen for myelination mutants, we identified a mutation in zinc finger protein 16-like (znf16l). znf16l mutant larvae have reduced myelin basic protein (mbp) expression and reduced CNS myelin. Marker, time-lapse and ultrastructural studies indicated that oligodendrocyte specification, migration and myelination are disrupted in znf16l mutants. Transgenic studies indicated that znf16l acts autonomously in oligodendrocytes. Expression of Zfp488 from mouse rescued mbp expression in znf16l mutants, indicating that these homologs have overlapping functions. Our results defined the function of a new zinc finger protein with specific function in oligodendrocyte specification, migration and myelination in the developing CNS.

ATAF2 integrates Arabidopsis brassinosteroid inactivation and seedling photomorphogenesis [RESEARCH ARTICLES]


Hao Peng, Jianfei Zhao, and Michael M. Neff

The Arabidopsis thaliana hypocotyl is a robust system for studying the interplay of light and plant hormones, such as brassinosteroids (BRs), in the regulation of plant growth and development. Since BRs cannot be transported between plant tissues, their cellular levels must be appropriate for given developmental fates. BR homeostasis is maintained in part by transcriptional feedback regulation loops that control the expression of key metabolic enzymes, including the BR-inactivating enzymes BAS1 (CYP734A1, formerly CYP72B1) and SOB7 (CYP72C1). Here, we find that the NAC transcription factor (TF) ATAF2 binds the promoters of BAS1 and SOB7 to suppress their expression. ATAF2 restricts the tissue-specific expression of BAS1 and SOB7 in planta. ATAF2 loss- and gain-of-function seedlings have opposite BR-response phenotypes for hypocotyl elongation. ATAF2 modulates hypocotyl growth in a light-dependent manner, with the photoreceptor phytochrome A playing a major role. The photomorphogenic phenotypes of ATAF2 loss- and gain-of-function seedlings are suppressed by treatment with the BR biosynthesis inhibitor brassinazole. Moreover, the disruption of BAS1 and SOB7 abolishes the short-hypocotyl phenotype of ATAF2 loss-of-function seedlings in low fluence rate white light, demonstrating an ATAF2-mediated connection between BR catabolism and photomorphogenesis. ATAF2 expression is suppressed by both BRs and light, which demonstrates the existence of an ATAF2-BAS1/SOB7-BR-ATAF2 feedback regulation loop, as well as a light-ATAF2-BAS1/SOB7-BR-photomorphogenesis pathway. ATAF2 also modulates root growth by regulating BR catabolism. As it is known to regulate plant defense and auxin biosynthesis, ATAF2 therefore acts as a central regulator of plant defense, hormone metabolism and light-mediated seedling development.

Evidence for the involvement of fibroblast growth factor 10 in lipofibroblast formation during embryonic lung development [RESEARCH ARTICLES]


Denise Al Alam, Elie El Agha, Reiko Sakurai, Vahid Kheirollahi, Alena Moiseenko, Soula Danopoulos, Amit Shrestha, Carole Schmoldt, Jennifer Quantius, Susanne Herold, Cho-Ming Chao, Caterina Tiozzo, Stijn De Langhe, Maksim V. Plikus, Matthew Thornton, Brendan Grubbs, Parviz Minoo, Virender K. Rehan, and Saverio Bellusci

Lipid-containing alveolar interstitial fibroblasts (lipofibroblasts) are increasingly recognized as an important component of the epithelial stem cell niche in the rodent lung. Although lipofibroblasts were initially believed merely to assist type 2 alveolar epithelial cells in surfactant production during neonatal life, recent evidence suggests that these cells are indispensable for survival and growth of epithelial stem cells during adulthood. Despite increasing interest in lipofibroblast biology, little is known about their cellular origin or the molecular pathways controlling their formation during embryonic development. Here, we show that a population of lipid-droplet-containing stromal cells emerges in the developing mouse lung between E15.5 and E16.5. This is accompanied by significant upregulation, in the lung mesenchyme, of peroxisome proliferator-activated receptor gamma (master switch of lipogenesis), adipose differentiation-related protein (marker of mature lipofibroblasts) and fibroblast growth factor 10 (previously shown to identify a subpopulation of lipofibroblast progenitors). We also demonstrate that although only a subpopulation of total embryonic lipofibroblasts derives from Fgf10+ progenitor cells, in vivo knockdown of Fgfr2b ligand activity and reduction in Fgf10 expression lead to global reduction in the expression levels of lipofibroblast markers at E18.5. Constitutive Fgfr1b knockouts and mutants with conditional partial inactivation of Fgfr2b in the lung mesenchyme reveal the involvement of both receptors in lipofibroblast formation and suggest a possible compensation between the two receptors. We also provide data from human fetal lungs to demonstrate the relevance of our discoveries to humans. Our results reveal an essential role for Fgf10 signaling in the formation of lipofibroblasts during late lung development.

Flow dynamics control the location of sprouting and direct elongation during developmental angiogenesis [RESEARCH ARTICLES]


Siavash Ghaffari, Richard L. Leask, and Elizabeth A. V. Jones

Angiogenesis is tightly controlled by a number of signalling pathways. Although our understanding of the molecular mechanisms involved in angiogenesis has rapidly increased, the role that biomechanical signals play in this process is understudied. We recently developed a technique to simultaneously analyse flow dynamics and vascular remodelling by time-lapse microscopy in the capillary plexus of avian embryos and used this to study the hemodynamic environment present during angiogenic sprouting. We found that sprouts always form from a vessel at lower pressure towards a vessel at higher pressure, and that sprouts form at the location of a shear stress minimum, but avoid locations where two blood streams merge even if this point is at a lower level of shear stress than the sprouting location. Using these parameters, we were able to successfully predict sprout location in quail embryos. We also found that the pressure difference between two vessels is permissive to elongation, and that sprouts will either change direction or regress if the pressure difference becomes negative. Furthermore, the sprout elongation rate is proportional to the pressure difference between the two vessels. Our results show that flow dynamics are predictive of the location of sprout formation in perfused vascular networks and that pressure differences across the interstitium can guide sprout elongation.