By Irma Silva

The Kennedy College of Science, Department of Biological Sciences, invites you to attend a Master’s Thesis Proposal Defense by Nicholas LaFave entitled “Masticatory myosin expression in rodent jaw muscles: links between myosin isoform expression and mechanical advantage”

Location: Ball Hall 302
Date: Wednesday, Oct. 11, 2023
Time: 1:30 – 3:30 p.m.

Committee Members:

  • Committee Chair: Jeffrey Moore, Professor, Biological Sciences, University of Massachusetts Lowell
  • Matthew Gage, Associate Professor, Chemistry, University of Massachusetts Lowell
  • Nicolai Konow, Assistant Professor, Biological Sciences, University of Massachusetts Lowell

Masticatory myosin (MHC-M), commonly referred to as MYH16, is an ancient vertebrate isoform of the sarcomeric protein myosin. MHC-M is found in jaw-closing muscles derived from the first pharyngeal arch of certain vertebrate species, most often carnivorous species or omnivorous species, or species that feed on nuts or other tough plant matter, suggesting that MHC-M provides an advantage when eating demanding foods (and may also provide an advantage for defensive biting). While MHC-M has been identified in a wide variety of vertebrates, it remains unclear how the jaw mechanical properties (such as mechanical advantage) of a MHC-M-containing clade relate to the relative myosin isoform composition, which will help determine its importance to the overall function of the jaw, most importantly regarding feeding. The main goal of this research is to determine whether only jaw-closing muscles of the first pharyngeal arch express MHC-M and find out whether there is a link between the presence of MHC-M and the mechanical properties of the jaw. The proposed work may provide insight into the conservation of MHC-M in some species but not in others, even if the species are closely related. It is hypothesized that to achieve a strong bite, rodents must either: 1) express MHC-M in the jaw muscles, or 2) possess specific leverage advantages and/or beneficial muscle architecture to increase muscle force. To determine what can achieve a strong bite, a cohort of myosin isoforms will be purified from the jaw-closing muscles of several species within the order Rodentia. Within the Rodentia phylogeny exists three different skull/jaw configurations that have been hypothesized to be related to differences in diet and feeding styles, with associated species containing various mixtures of MHC-M with other isoforms, from mostly MHC-M, to no MHC-M. Myosin purified from the jaw muscles of six species in the order Rodentia covering three major rodent skull types (Myomorphs, Sciuromorphs, Hystricomorphs) will be compared via modified SDS-PAGE and gel densitometry. Western blotting and/or mass spectrometry will be performed when necessary (e.g., when myosin isoform identification is not clear based on gel mobility). Myosin isoform composition will be compared to whole muscle contractile measurements and physiological functioning (muscle physiological cross-sectional area, leverage) reported in the literature and/or obtained collaboratively. The proposed research will be the first to identify and compare myosin isoforms of several major jaw muscles of a cohort of common rodent species. Ultimately, myosin isoform information will be interpreted in the context of measurements of mechanical properties of the whole muscle performed by collaborators as well as the feeding styles of the chosen species. Additionally, this study will provide groundwork for future studies exploring the evolutionary history of jaw musculature and determine the advantage, if any, provided by MHC-M or lack thereof.