Biology subjects

Baba, S. A.

Publications and source records attributed to Baba, S. A..

3 recordsLinked to original sources

bioRxiv2023

Swimming ability and flagellar motility of sperm packets of the volvocine green alga Pleodorina starrii

Eukaryotic flagella collectively form metachronal waves that facilitate the ability to cause flow or swim. Among such flagellated and planktonic swimmers, large volvocine genera such as Eudorina, Pleodorina and Volvox form bundles of small male gametes (sperm) called "sperm packets" for sexual reproduction. Although these sperm packets reportedly have flagella and the ability to swim, previous studies on volvocine motility have focused on asexual forms and the swimming characteristics of sperm packets remain unknown. However, it is important to quantify the motility of sperm packets and sperm in order to gain insights into the significance of motility in the sexual reproduction of planktonic algae. In this study, we quantitatively described the behavior of three flagellated forms of a male strain of Pleodorina starrii--asexual colonies, sperm packets, and single dissociated sperm--with emphasis on comparison of the two multicellular forms. Despite being smaller, sperm packets swam approximately 1.4 times faster than the asexual colonies of the same male strain. Body length was approximately 0.5 times smaller in the sperm packets than in asexual colonies. The flagella from sperm packets and asexual colonies showed asymmetric waveforms, whereas those from dissociated single sperm showed symmetric waveforms, suggesting the presence of a switching mechanism between sperm packets and dissociated sperm. Flagella from sperm packets were approximately 0.5 times shorter and had a beat period approximately twice as long as those from asexual colonies. The flagella of sperm packets were densely distributed over the anterior part of the body, whereas the flagella of asexual colonies were sparse and evenly distributed. The distribution of flagella, but not the number of flagella, appear to illustrate a significant difference in the speeds of sperm packets and asexual colonies. Our findings reveal novel aspects of the regulation of eukaryotic flagella and shed light on the role of flagellar motility in sexual reproduction of planktonic algae.

biophysics↗

bioRxiv2022

Acquirement of the autonomic nervous system modulation evaluated by heart rate variability in medaka (Oryzias latipes)

Small teleosts have recently been established as models of human diseases. However, measuring heart rate by electrocardiography is highly invasive for small fish. The physiological nature and function of vertebrate autonomic nervous system (ANS) modulation of the heart has traditionally been investigated in larvae with an incompletely developed ANS or in anesthetized adults, whose ANS activity may possibly be disturbed under anesthesia. Here, we defined the frequency characteristics of heart rate variability (HRV) modulated by the ANS from observations of heart movement in high-speed movie images and changes in ANS regulation under environmental stimulation in unanesthetized adult medaka (Oryzias latipes), a small teleost. The HRV was significantly reduced by atropine (1 mM) in the 0.25 - 0.65 Hz and by propranolol (100 M) at 0.65-1.25 Hz range, suggesting that HRV in adult medaka is modulated by both the parasympathetic and sympathetic nervous systems within these frequency ranges. Such modulations of HRV by the ANS were remarkably suppressed in anesthetized adult medaka. Continuous exposure to light suppressed HRV only in the 0.25 - 0.65 Hz range, indicating parasympathetic withdrawal. The power of HRV increased along developmental processes. These results suggest that ANS modulation of the heart in adult medaka is frequency-dependent phenomenon, and that the impact of long-term environmental stimuli on ANS activities can be precisely evaluated in unanesthetized adult fish using this method.

physiology↗

bioRxiv2020

Calaxin is essential for the transmission of Ca2+-dependent asymmetric waves in sperm flagella

Regulation of waveform asymmetry in sperm flagella is critical for changes in sperm swimming trajectory as seen during sperm chemotaxis towards eggs. Ca2+ is known as an important regulator of asymmetry in flagellar waveforms. A calcium sensor protein, calaxin, which is associated with the outer arm dynein, plays a key role in the sperm waveform regulation in a Ca2+-dependent manner. However, the molecular mechanism underlying the regulation of asymmetric waves by Ca2+ and calaxin remains unclear. We performed experiments using caged ATP to elucidate the formation and propagation of asymmetric flagellar waves in the sperm of the ascidian Ciona intestinalis. Demembranated sperm cells were suspended in a solution containing caged ATP and reactivated using UV flash photolysis. Initial bends were formed at the base and propagated towards the tip of flagella; however, the bend direction was different between asymmetric and symmetric waves. A calaxin inhibitor, repaglinide, had no effect on initial bend formation, but significantly inhibited the generation of the second flagellar bend in the reverse direction, resulting in the failure of asymmetric wave formation and propagation. These results suggest that calaxin plays a critical role in Ca2+-dependent transmission of flagellar asymmetric waveforms.

cell biology↗