An F-Actin Mega-Cable Is Associated With the Migration of the Sperm Nucleus During the Fertilization of the Polarity-Inverted Central Cell of Agave inaequidens

Abstract

Asparagaceae’s large embryo sacs display a central cell nucleus polarized toward the chalaza, which means the sperm nucleus that fuses with it during double fertilization migrates an atypical long distance before karyogamy. Because of the size and inverted polarity of the central cell in Asparagaceae, we hypothesize that the second fertilization process is supported by an F-actin machinery different from the short-range F-actin structures observed in Arabidopsis and other plant models. Here, we analyzed the F-actin dynamics of Agave inaequidens, a classical Asparagaceae, before, during, and after the central cell fertilization. Several parallel F-actin cables, spanning from the central cell nucleus to the micropylar pole, and enclosing the vacuole, were observed. As fertilization progressed, a thick F-actin mega-cable traversing the vacuole appeared, connecting the central cell nucleus with the micropylar pole near the egg cell. This mega-cable wrapped the sperm nucleus in transit to fuse with the central cell nucleus. Once karyogamy finished, and the endosperm started to develop, the mega-cable disassembled, but new F-actin structures formed. These observations suggest that Asparagaceae, and probably other plant species with similar embryo sacs, evolved an F-actin machinery specifically adapted to support the migration of the fertilizing sperm nucleus within a large-sized and polarity-inverted central cell.

Comparative Transcriptome Sequencing Analysis of Hirudo nipponia in Different Growth Periods

“…For example, SPA17, IQCG, ACTB, 5-HT , and the HOX gene family. The IQCG is also involved in spermatogenesis and is a key regulator of cilia/flagellar motility and is associated with sperm motility ( Harris et al, 2014 ; Gonzalez-Gutierrez et al, 2021 ). Additionally, the studies have also reported that β -actin is potentially involved in sperm maturation, sperm excretion, and the ability to maintain sperm motility.…”

Cellular dynamics of endosperm development in Arabidopsis thaliana

“…In both plants and animals, cytoskeletal structures such as actin filaments (F-actin) and microtubules (MTs) regulate many fundamental cellular processes [18][19][20][21][22][23][24][25] , including those in plant reproduction such as pollen tube growth and guidance, sperm nuclear migration, and asymmetric division of the zygote [18][19][20][26][27][28] . Immunostaining studies of coenocytic endosperm at interphase revealed a nucleus-based radial MT (aster-shaped) system that organizes cytoplasm into nuclearcytoplasmic domains [21][22][23][24] .…”