Cytodifferentiation of hair cells during the development of a basal chordate

Tunicates are unique animals for studying the origin and evolution of vertebrates because they are considered vertebrates' closest living relatives and share the vertebrate body plan and many specific features. Both possess neural placodes, transient thickenings of the cranial ectoderm that give rise to various types of sensory cells, including axonless secondary mechanoreceptors. In vertebrates, these are represented by the hair cells of the inner ear and the lateral line, which have an apical apparatus typically bearing cilia and stereovilli. In tunicates, they are found in the coronal organ, which is a mechanoreceptor located at the base of the oral siphon along the border of the velum and tentacles and is formed of cells bearing a row of cilia and short microvilli. The coronal organ represents the best candidate homolog for the vertebrate lateral line. To further understand the evolution of secondary sensory cells, we analysed the development and cytodifferentiation of coronal cells in the tunicate ascidian Ciona intestinalis for the first time. Here, coronal sensory cells can be identified as early as larval metamorphosis, before tentacles form, as cells with short cilia and microvilli. Sensory cells gradually differentiate, acquiring hair cell features with microvilli containing actin and myosin VIIa; in the meantime, the associated supporting cells develop. The coronal organ grows throughout the animal's lifespan, accompanying the growth of the tentacle crown. Anti-phospho Histone H3 immunostaining indicates that both hair cells and supporting cells can proliferate. This finding contributes to the understanding of the evolution of secondary sensory cells, suggesting that both ancestral cell types were able to proliferate and that this property was progressively restricted to supporting cells in vertebrates and definitively lost in mammals.

Onset of sheath extension and duration of lamina extension are major determinants of the response of maize lamina length to plant density

BACKGROUND AND AIMS

Plants regulate their architecture strongly in response to density, and there is evidence that this involves changes in the duration of leaf extension. This questions the approximation, central in crop models, that development follows a fixed thermal time schedule. The aim of this research is to investigate, using maize as a model, how the kinetics of extension of grass leaves change with density, and to propose directions for inclusion of this regulation in plant models.

METHODS

Periodic dissection of plants allowed the establishment of the kinetics of lamina and sheath extension for two contrasting sowing densities. The temperature of the growing zone was measured with thermocouples. Two-phase (exponential plus linear) models were fitted to the data, allowing analysis of the timing of the phase changes of extension, and the extension rate of sheaths and blades during both phases.

KEY RESULTS

The duration of lamina extension dictated the variation in lamina length between treatments. The lower phytomers were longer at high density, with delayed onset of sheath extension allowing more time for the lamina to extend. In the upper phytomers--which were shorter at high density--the laminae had a lower relative extension rate (RER) in the exponential phase and delayed onset of linear extension, and less time available for extension since early sheath extension was not delayed.

CONCLUSIONS

The relative timing of the onset of fast extension of the lamina with that of sheath development is the main determinant of the response of lamina length to density. Evidence is presented that the contrasting behaviour of lower and upper phytomers is related to differing regulation of sheath ontogeny before and after panicle initiation. A conceptual model is proposed to explain how the observed asynchrony between lamina and sheath development is regulated.

Infrequent replication errors at microsatellite loci in tumors of patients with multiple primary cancers of the esophagus and various other tissues

Patients with esophageal cancer are at high risk of developing other primary tumors, especially squamous cell carcinoma in the head and neck. Heavy smoking and excessive consumption of alcohol are considered to be crucial environmental risk-factors for development of these multiple primary cancers. To investigate whether any genetic background, such as defects in the DNA-mismatch repair system, may influence the development of these multiple primary tumors, we examined replication errors (RER) at six microsatellite loci in DNAs of 46 tumors from 33 patients who had developed primary cancers in various tissues in addition to the esophagus. RER(+) (RER-positive) phenotype was observed in three tumors in two patients of the 33 patients examined. Our results suggested that development of multiple primary tumors in these patients would not be affected by an abnormality in the DNA repair system(s) detected as the RER phenotype. However, it is noteworthy that a single patient who developed multiple cancers revealed RER(+) phenotypes at multiple microsatellite loci in both tumors, indicating that a defect in the DNA repair gene(s) may have played an important role in the development of the tumors in this patient.