Microtubules and control of insect egg shape

Area of Science:

• Developmental Biology
• Cell Biology
• Biophysics

Background:

• Insect oocytes and surrounding follicles exhibit anisotropic growth, adopting prolate spheroid shapes.
• Surface growth is polarized, with faster expansion along the polar axis and slower expansion circumferentially.

Purpose of the Study:

• To investigate the role of microtubules and desmosomes in transmitting tensile forces during isometric growth of insect follicular epithelium.
• To understand the contribution of follicular mechanical properties to the final shape of insect eggs.

Main Methods:

• Observation of microtubule bundle orientation in follicle cells of *Heteropeza* and *Periplaneta*.
• Analysis of microtubule attachment to spot desmosomes at cell boundaries.
• Inference of mechanical force transmission based on structural organization.

Main Results:

• Microtubule bundles in follicle cells are oriented circumferentially, perpendicular to the egg's polar axis.
• Microtubules appear connected to desmosomes at cell-cell junctions.
• A mechanical continuum is proposed, formed by microtubules and desmosomes, transmitting tensile forces circumferentially.

Conclusions:

• Microtubules and desmosomes form a network that transmits tensile forces within the follicular epithelium.
• This follicular resistance to circumferential expansion is a key factor in determining the elongated shape of insect eggs.