High impact information on epha4a

• Function of the Eph-related kinase rtk1 in patterning of the zebrafish forebrain [1].
• A new interface between otx2 and epha4a suggests that the rostralization stops at the caudal part of rhombomere 1 [2].
• In support of this hypothesis, we show that it is possible to rescue boundary formation in fss(-) through the ectopic expression of EphA4, an anterior segment marker, in the paraxial mesoderm [3].
• As gastrulation proceeds, both rtk1 and rtk2 are expressed within the axial hypoblast along the entire axis of the embryo [4].
• However, in mosaic embryos, we observe that EphA4MO cells and EphA4-expressing cells sort from one another, an observation that is not predicted by the Eph-ephrin repulsion model but instead suggests that EphA4 promotes cell adhesion within the rhombomeres in which it is expressed [5].

Biological context of epha4a

• EphA4 is required for cell adhesion and rhombomere-boundary formation in the zebrafish [5].
• EphA4 was also detected during sensory organogenesis, in the developing ear, eye, nasal pits and lateral line [6].
• In order to determine which components of EphA4 function may be primitive for gnathostomes, we cloned EphA4 from the lesser spotted catshark ( Scyliorhinus canicula) and examined its expression pattern during shark embryonic development [6].

Anatomical context of epha4a

• Formation of the DMB is also defective as shown by a caudal expansion of diencephalic epha4a and pax6a expression into midbrain territory [7].
• Third, activation of EphA4 leads to nonautonomous acquisition of columnar morphology and polarized relocalization of the centrosome and nucleus in cells on the opposite side of the forming boundary [8].
• Second, activation of EphA4 leads to the cell-autonomous acquisition of a columnar morphology and apical redistribution of beta-catenin, aspects of epithelialization characteristic of cells at somite boundaries [8].
• Consistent with the patterns reported for bony fish and tetrapods, we observed segmental expression of EphA4 in the developing hindbrain and later in the pharyngeal arches of shark embryos [6].
• Analyses of EphA4 in mouse, chick, frog and zebrafish embryos have implicated this gene in a number of developmental processes, including maintenance of segmental boundaries, axon guidance, limb development, neural crest migration and patterning of the ear [6].

Other interactions of epha4a

• This sorting-out process has been shown to involve repulsive interactions between cells expressing an Eph receptor tyrosine kinase, EphA4, and cells expressing its ephrinB ligands [5].

References