Asynchrony of Developmental Markers in Embryonic Mice: The Need for a New System

Open Access
Author:
Mazzocco, Vivianne Elaine
Area of Honors:
Biological Anthropolgy
Degree:
Bachelor of Arts
Document Type:
Thesis
Thesis Supervisors:
  • Joan Therese Richtsmeier, Thesis Supervisor
  • Timothy Michael Ryan, Honors Advisor
Keywords:
  • embryo
  • embryology
  • mouse models
  • mice
  • prenatal
  • development
  • staging system
  • limb bud
  • digit separation
  • whisker
Abstract:
Mice are the primary model organisms used to study mammalian embryological development. Consequently, researchers have intricately described their developmental features and sequence, and have used these traits to establish biological staging systems on the basis of age-specific developmental markers (e.g. number of somites, crown-rump length, limb bud development, craniofacial morphology). However, little research has been done to examine the magnitude of variation present within mice that are of the same chronological age (number of days of development post conception). Indeed, individuals within litters are known to be of different ages as egg fertilization takes place individually so the timing of each conception is unique. As proof of this, genetically invariant littermates often show signs of being of different developmental ages, an observations that means that the conception of the embryos occurred at different times and that each embryo may follow a different growth trajectory and potentially grow at a different rate. Due to these differences, a different age may be estimated for an embryo depending upon which morphological element and corresponding staging system is used. In this study, crown-rump length, digit development, and whisker and facial follicle presence were recorded for mouse embryos between embryonic days 12 through 16 (E12 - E16). These data were used to characterize the structure of variation in these traits during this embryonic period and to determine whether these patterns reveal coordinated or asynchronous development across systems. My results indicate wide variation across traits and developmental timing. Significant overlap occurs in the younger ages (i.e. E12 - E14) for crown-rump length and limb bud maturation, while the older embryos (i.e. E15 -16) exhibit increased variation within the measured traits.