Brain growth and neocortical development in the opossum

Area of Science:

• Neuroscience
• Developmental Biology
• Comparative Anatomy

Background:

• Marsupials exhibit unique developmental timelines compared to eutherian mammals.
• Understanding marsupial brain development provides insights into conserved and divergent evolutionary pathways.
• Didelphis virginiana offers a model for studying early mammalian brain development due to its altricial birth state.

Purpose of the Study:

• To investigate the general brain growth and neocortical differentiation in Didelphis virginiana from embryonic stages to adulthood.
• To determine the timing and pattern of neocortical development, specifically focusing on the emergence of the cortical plate and lamination.
• To compare the developmental trajectory of the Didelphis virginiana neocortex with that of eutherian mammals.

Main Methods:

• Embryonic and postnatal specimens of Didelphis virginiana were analyzed.
• Developmental stages were examined from 10.5 days of embryonic development through adulthood.
• Histological analysis was employed to observe brain growth, differentiation, and cortical lamination patterns.

Main Results:

• Didelphis virginiana is born at an embryonic stage (12.5 days gestation) with a two-layered telencephalic wall.
• Neocortical development, including the appearance of the cortical plate, occurs postnatally, primarily after the first postnatal week.
• Cortical lamination becomes evident by postnatal day 35, with a well-defined six-layered neocortex by postnatal day 60, similar to eutherian mammals.

Conclusions:

• Neocortical development in Didelphis virginiana is a predominantly postnatal phenomenon.
• The developmental pattern and establishment of the six-layered neocortex in this marsupial are comparable to those observed in eutherian mammals.
• This study highlights conserved mechanisms in mammalian neocortical development despite divergent reproductive strategies.