Biology subjects

Mead, A. F.

Publications and source records attributed to Mead, A. F..

4 recordsLinked to original sources

bioRxiv2026

Thermal acclimation and resultant developmental adaptation offsets environmental temperature effects on tail muscle mechanics in larval zebrafish

Environmental temperature strongly influences muscle contractile mechanics and locomotor performance in ectotherms, yet animals routinely develop across a range of temperatures while maintaining effective movement. We tested the hypothesis that developmental temperature induces compensatory changes in the intrinsic mechanical properties of the muscles that power the fast-start escape response in larval zebrafish (Danio rerio). Larvae were reared at 25{degrees}C, 28{degrees}C, or 32{degrees}C, and contractile properties of intact tail myotomal muscles were measured across experimental temperatures. Acute changes in experimental temperature strongly affected twitch kinetics, particularly relaxation rate (Q10 = 2.1), resulting in substantial changes in twitch duration. In contrast, rearing temperature produced adaptive changes that opposed these acute thermal effects. At a common experimental temperature, muscles from cold-reared larvae exhibited faster intrinsic relaxation and greater force production during shortening at a physiologically relevant velocity, whereas warm-reared larvae showed slower relaxation and reduced shortening force. As a result, twitch kinetics were largely normalized when measurements were made at each group's rearing temperature, reducing the apparent thermal sensitivity of relaxation rate (Q10 = 1.1). To identify molecular correlates of these functional adaptations, we performed label-free quantitative LCMS proteomic analysis. Cold rearing increased the abundance of Sarco/Endoplasmic Reticulum Calcium-ATPase (SERCA) proteins, driven primarily by elevated atp2a1 expression, while warm rearing reduced the abundance of the major parvalbumin isoforms pvalb1 and pvalb2. These changes implicate remodeling of intracellular calcium handling as a mechanism underlying thermal compensation of muscle function. Together, our results demonstrate that developmental temperature modifies the intrinsic mechanical properties of larval zebrafish muscle in ways that counteract the direct effects of environmental temperature, thereby preserving the timing and power-generating capacity required for fast-start escape performance.

physiology↗

bioRxiv2024

Functional role of myosin-binding protein H in thick filaments of developing vertebrate fast-twitch skeletal muscle

Myosin-binding protein H (MyBP-H) is a component of the vertebrate skeletal muscle sarcomere with sequence and domain homology to myosin-binding protein C (MyBP-C). Whereas skeletal muscle isoforms of MyBP-C (fMyBP-C, sMyBP-C) modulate muscle contractility via interactions with actin thin filaments and myosin motors within the muscle sarcomere "C-zone," MyBP-H has no known function. This is in part due to MyBP-H having limited expression in adult fast-twitch muscle and no known involvement in muscle disease. Quantitative proteomics reported here reveal MyBP-H is highly expressed in prenatal rat fast-twitch muscles and larval zebrafish, suggesting a conserved role in muscle development, and promoting studies to define its function. We take advantage of the genetic control of the zebrafish model and a combination of structural, functional, and biophysical techniques to interrogate the role of MyBP-H. Transgenic, FLAG-tagged MyBP-H or fMyBP-C both localize to the C-zones in larval myofibers, whereas genetic depletion of endogenous MyBP-H or fMyBP-C leads to increased accumulation of the other, suggesting competition for C-zone binding sites. Does MyBP-H modulate contractility from the C-zone? Globular domains critical to MyBP-Cs modulatory functions are absent from MyBP-H, suggesting MyBP-H may be functionally silent. However, our results suggest an active role. Small angle x-ray diffraction of intact larval tails revealed MyBP-H contributes to the compression of the myofilament lattice accompanying stretch or contraction, while in vitro motility experiments indicate MyBP-H shares MyBP-Cs capacity as a molecular "brake". These results provide new insights and raise questions about the role of the C-zone during muscle development.

biophysics↗

bioRxiv2020

Mechanical characteristics of ultrafast zebrafish larval swimming muscles

Zebrafish (Danio rerio) swim within days of fertilization, powered by muscles of the axial myotomes. Forces generated by these muscles can be measured rapidly in whole, intact larval tails by adapting protocols developed for ex vivo muscle mechanics. But it is not known how well these measurements reflect the function of the underlying muscle fibers and sarcomeres. Here we consider the anatomy of the 5-day-old, wild-type larval tail, and implement technical modifications to measuring muscle physiology in intact tails. Specifically, we quantify fundamental relationships between force, length, and shortening velocity, and capture the extreme contractile speeds required to swim with tail-beat frequencies of 80-100 Hz. Therefore, we analyze 1000 frames/second movies to track the movement of structures, visible in the transparent tail, which correlate with sarcomere length. We also characterize the passive viscoelastic properties of the preparation to isolate forces contributed by non-muscle structures within the tail. Myotomal muscles generate more than 95% of their maximum isometric stress (76{+/-}3 mN/mm2) over the range of muscle lengths used in vivo. They have rapid twitch kinetics (full width at half-maximum stress: 11{+/-}1 msec) and a high twitch to tetanus ratio (0.91{+/-}0.05), indicating adaptations for fast excitation-contraction coupling. Although contractile stress is relatively low, myotomal muscles develop high net power (134{+/-}20 W/kg at 80 Hz) in cyclical work loop experiments designed to simulate the in vivo dynamics of muscle fibers during swimming. When shortening at a constant speed of 7{+/-}1 muscle lengths/second, muscles develop 86{+/-}2% of isometric stress, while peak instantaneous power during 100Hz work loops occurs at 18{+/-}2 muscle lengths/second. These approaches can improve the usefulness of zebrafish as a model system for muscle research by providing a rapid and sensitive functional readout for experimental interventions. Statement of significanceThe zebrafish (Danio rerio) may prove a uniquely efficient model system for characterizing vertebrate muscle physiology. Transparent, drug-permeable larva - each, in essence, a fully functional muscle - can be generated rapidly, inexpensively, and in large numbers. Critically, the zebrafish genome contains homologs of major muscle genes and is highly amenable to manipulation. To reach its potential, reliable (and preferably rapid) means are needed to observe the effects of experimental interventions on larval muscle function. In the present study we show how mechanical measurements made on whole, intact larval tails can provide a readout of fundamental muscle-mechanical properties. Additionally, we show that these muscles are among the fastest ever measured, and therefore worthy of study in their own right.

physiology↗

bioRxiv2017

Fundamental Constraints In Synchronous Muscle Limit Superfast Motor Control In Vertebrates

Superfast muscles (SFM) are extremely fast synchronous muscles capable of contraction rates up to 250 Hz, enabling precise motor execution at the millisecond time scale. To allow such speed, the archetypal SFM, found in the toadfish swimbladder, has hallmark structural and kinetic adaptations at each step of the conserved excitation-contraction coupling (ECC) pathway. More recently SFM phenotypes have been discovered in most major vertebrate lineages, but it remains unknown whether all SFM share ECC adaptations for speed, and if SFM arose once, or from independent evolutionary events. Here we use genomic analysis to identify the myosin heavy chain genes expressed in bat and songbird SFM to achieve rapid actomyosin crossbridge kinetics and demonstrate that these are evolutionarily and ontologically distinct. Furthermore, by quantifying cellular morphometry and calcium signal transduction combined with force measurements we show that all known SFM share multiple functional adaptations that minimize ECC transduction times. Our results suggest that SFM evolved independently in sound producing organs in ray-finned fish, birds, and mammals, and that SFM phenotypes operate at a maximum operational speed set by fundamental constraints in synchronous muscle. Consequentially, these constraints set a fundamental limit to the maximum speed of fine motor control.

physiology↗