Biology subjects

Nakamoto, A.

Publications and source records attributed to Nakamoto, A..

3 recordsLinked to original sources

bioRxiv2025

Disruption of spindle orientation and protein localization during asymmetric cleavage by pharmacological inhibition of serotonin signaling

Cell polarity directs the orientation and size of asymmetric cell divisions, and the segregation of cell fate determinants processes fundamental to development in all multicellular organisms. During asymmetric cleavage, the mitotic spindle aligns with a specified polarity of the mother cell, and cell fate determinants are distributed asymmetrically along the division axis. Here, we report that pharmacological inhibition of serotonin signaling during the 4-to-8-cell division in early embryos of the mud snail Ilyanassa obsoleta (currently known as Tritia obsoleta) disrupts the typical unequal division pattern. The oblique axis of division common to spirally cleaving molluscan embryos is altered, and the position of the mitotic spindle is randomized in these treatments. Mother cells generate abnormally large, atypically positioned daughter cells. We also find that, in normal embryos, proteins recognized by phosphorylated PKC and Bazooka/PAR-3 antibodies typically co-localize with the spindle apparatus to the apical cortex of each mother cell. These antigens subsequently segregate to the smaller of the two daughter cells. In embryos treated with the serotonin-receptor antagonist, the localization of these asymmetrically segregating proteins is randomized, and their localization is independent of spindle position. These results suggest that serotonin signaling coordinates spindle orientation, cortical polarity, and cell size in early asymmetric cleavages. HighlightsO_LIThis study suggests a novel rule for serotonin signaling in asymmetric cleavage C_LIO_LISerotonin-receptor antagonist treatment disrupts typical asymmetric cleavage C_LIO_LIaPKC and Bazooka/PAR-3 localize with the spindle at the apical cortex C_LIO_LIInhibition of serotonin signaling disrupts localization of the polarity proteins C_LIO_LISerotonin may regulate division through G-protein effects on the cytoskeleton C_LI

developmental biology↗

bioRxiv2024

Horizontal transmission of functionally diverse transposons is a major source of new introns

Specialized transposable elements (TEs), introners, are one of the major drivers of intron gain in diverse eukaryotes. However, the molecular mechanism(s) and evolutionary processes driving introner propagation within and between lineages remain elusive. We analyze 8716 genomes, revealing 1093 introner families in 201 species spanning 1.7 billion years of evolution. Introners are derived from functionally diverse TEs including families of terminal-inverted-repeat DNA TEs, retrotransposons, cryptons, and helitrons as well as mobile elements with unknown molecular mechanisms. We identify eight cases where introners recently transferred between divergent host species, and show that giant viruses that integrate into genomes may facilitate introner transfer across lineages. We propose that intron gain is an inevitable consequence of TE activity in eukaryotic lineages, thereby resolving a key mystery of genome structure evolution.

genomics↗

bioRxiv2023

Embryonic organizer specification in the mud snail Ilyanassa obsoleta depends on intercellular signaling

In early embryos of the neogastropod Ilyanassa obsoleta, cytoplasmic segregation of a polar lobe is required for establishment of the D macromere, empowering its great-granddaughter macromere 3D to act as a single-celled organizer that induces body patterning along the secondary axis. We present evidence that polar lobe inheritance is not sufficient to specify 3D potential, but rather makes the D macromere lineage responsive to some intercellular signal(s) required for activating the special properties of 3D. Experimental removal of micromeres results in loss of organizer-linked MAPK activation, complete and specific defects of organizer-dependent larval organs, and progressive cell cycle retardation leading to equalization of the normally accelerated division schedule of 3D. Ablation of the second-quartet micromere 2d greatly potentiates the effects of first-quartet micromere ablation. Our findings link 3D establishment in I. obsoleta to the putative ancestral spiralian mechanism in which a signal from micromeres leads to specification of 3D among four initially equivalent macromeres. Summary StatementCell ablation experiments on embryos of the snail Ilyanassa reveal that specification of the organizer cell 3D depends on cell-extrinsic cues as well as polar lobe inheritance.

developmental biology↗