Table of Contents
Last Updated: November 3, 2025
Estimated reading time: ~6 minutes
Word count: 1389
How does an arthropod cell physically migrate and secrete a new exoskeleton? While we can observe the overall process of wound healing, understanding the *mechanism* requires a much closer look. This summary explores the electron microscopy findings from Archana Dutt’s 1977 thesis, revealing the specific arthropod wound ultrastructure—the microscopic cellular machinery—that makes repair possible in the scorpion, Palamnaeus bengalensis.
- Electron microscopy shows that activated epidermal cells become “factories,” rapidly increasing organelles like Golgi bodies, rough ER, and microtubules.
- Migrating cells were observed to use a “ruffled membrane,” a key structure in cell locomotion.
- The new cuticle is secreted into highly folded microvilli on the cell’s surface, maximizing the secretion area.
- The basement membrane (the cell’s anchor) becomes visibly disorganized and fragmented to allow cell migration.
Arthropod Wound Ultrastructure: Inside the Healing Cell
The Activated Epidermal Cell: A ‘Factory’ for Repair
Professor’s Insight: This is a classic example of cellular form following function. The sudden appearance of these organelles is the cell visibly “tooling up” for the two specific jobs it must perform: move (microtubules) and secrete (ER and Golgi).
At the ultrastructural level, an epidermal cell near a wound looks drastically different from a resting cell. Electron micrographs show that activated cells become packed with the specific organelles needed for synthesis and movement.
The activated epidermal cells at the wound site of 4 day old wounds, however, showed an increase in the number of rough endoplasmic reticulum, Golgi bodies… and microtubules, when compared with the normal epidermal cells. (Dutt, 1977, p. 55).
In a normal, resting epidermal cell, the cytoplasm is relatively simple [p. 51]. However, in cells activated by a nearby wound, the change is dramatic. The thesis describes a significant increase in rough endoplasmic reticulum (RER) and Golgi bodies. In cell biology, this combination is the quintessential “protein factory.” The RER synthesizes the proteins (like arthrodin) needed for the new cuticle, and the Golgi bodies package and modify them for secretion. Furthermore, the appearance of abundant microtubules is critical [p. 55]. These tiny tubules act as an internal scaffolding, providing the cell with the rigidity and framework it needs to change shape and migrate. They also function as “highways” for transporting vesicles (the packages from the Golgi) to the cell surface.
Student Note: For an exam, if you are asked how an epidermal cell prepares for secretion, the key answer is the **proliferation of the RER and Golgi apparatus**. The presence of microtubules is the key indicator of preparation for *cell movement*.
Cellular Locomotion and the ‘Ruffled Membrane’
Professor’s Insight: The “ruffled membrane” (a term for what we now often call a lamellipodium) is the cell’s “foot.” Observing this proved that the cells were actively “crawling” over the haemocyte plug, not just being passively pushed into place.
The thesis confirms that epidermal cells actively migrate, or crawl, to cover the wound. This movement is driven by a specialized structure at the cell’s leading edge, described as a “ruffled membrane.”
Some cells… showed the ‘ruffled membrane’ at the upper plasma membrane edge of the activated epidermal cell… This was a clear indication that the epidermal cells migrate over the haemocyte platform… (Dutt, 1977, p. 53).
This “ruffled membrane” is a dynamic, wave-like extension of the cell membrane at its migrating front. The thesis’s introduction cites Abercrombie (1961) and Clark and Harvey (1965) [p. 10], showing this finding aligns with leading theories of cell locomotion. This structure actively “feels” and pulls the cell forward over the substrate—in this case, the platform built by the haemocytes. The microtubules, observed in the previous section, would provide the internal structural support and direction for this “ruffling” action [p. 56].
The electron micrographs also captured desmosomes, or “spot welds,” between migrating cells [p. 53]. This shows that the cells move as a cohesive sheet, pulling each other along rather than migrating as individuals.
Student Note: The key locomotory structure identified at the ultrastructural level is the ‘ruffled membrane’ [p. 53]. This, combined with an internal microtubule network, facilitates the active migration of the epidermal sheet.
Secretion of the New Cuticle via Microvilli
Professor’s Insight: This folding mechanism is all about efficiency. To repair a large gap, the cell needs to dump a lot of material quickly. By folding its membrane, it dramatically increases the available surface area for secretion.
Once the epidermal cells are in position, they must deposit the new cuticle. The electron micrographs reveal *how* this is done: the top surface of the cell becomes highly folded to maximize its surface area for secretion.
The upper plasma membrane of the epidermal cell was greatly folded. The tips of the folds came to lie within electron lucent material… The space between the cuticle and the plasma membrane was filled with the granular material. (Dutt, 1977, p. 55).
This “granular material” is the new cuticle, likely a mix of chitin and protein precursors, being secreted by the cell. The “greatly folded” membrane describes what are known as microvilli. Instead of having a flat roof, the cell’s apical (top) surface develops dozens of these tiny projections. The new cuticle material is then secreted into the spaces and folds between these microvilli.
This is a far more efficient method of secretion than depositing from a flat surface. The thesis also identifies “muscle attachment fibres” [p. 55] and “pore canals” [p. 56] forming within this new cuticle, indicating the repair is not just a simple patch but an attempt to recreate a functional, integrated piece of exoskeleton.
Student Note: The new cuticle is not secreted from a flat surface. It is deposited into the spaces created by highly folded microvilli on the apical (upper) plasma membrane of the epidermal cells [p. 55].
The Disrupted Basement Membrane: Un-anchoring the Cells
Professor’s Insight: The images of the disrupted basement membrane are compelling. They show a controlled demolition, not a catastrophic failure. The cells must enzymatically dissolve their “floor” so they can move, and then rebuild it later.
Before an epidermal cell can migrate, it must detach from its anchor. The thesis provides clear ultrastructural evidence of this “un-anchoring” process, showing the normally strong, fibrous basement membrane in a state of disarray.
…the lower plasma membrane of the epidermal cell… [was] attached to a completely disorganised basement membrane… The basement membrane was attached loosely and now quite disorganised. (Dutt, 1977, p. 56-57).
In a normal state, the basement membrane is a continuous, clearly defined layer that supports the epidermis. The electron micrographs of the 17-day wound stage, however, show this membrane is “disorganised” and “fragmented” [p. 57, 56]. This confirms the light microscopy observation that the membrane is disrupted during migration [p. 6].
This breakdown is likely a necessary, enzyme-driven process initiated by the epidermal cells themselves to allow them to “lift off” and move. The thesis also notes that haemocytes are found attached to this disorganizing membrane [p. 57], which supports the hypothesis that they are involved in both the breakdown of the old membrane and the secretion of the new one.
Student Note: Migration requires detachment. This is achieved by the active, localized disorganization and fragmentation of the basement membrane, which frees the epidermal cells to move toward the wound center.
This content has been reviewed and edited by the Professor of Zoology editorial team. It is an original educational summary, and all directly quoted material from the 1977 thesis is explicitly cited.
Key Takeaways
- Cellular Activation: Healing epidermal cells are identified by an increase in secretion-related organelles (Golgi, rough ER) and movement-related structures (microtubules).
- Cellular Movement: Migration is an active “crawling” process driven by a “ruffled membrane” (lamellipodium) at the cell’s leading edge.
- Secretion Mechanism: The new cuticle is deposited into folds (microvilli) on the cell’s upper surface, a method that maximizes the surface area for secretion.
- Detachment for Migration: The basement membrane, which normally anchors the cells, becomes visibly “disorganised” and “fragmented” to allow the epidermal sheet to move.
MCQs
- A 4-day old wound shows epidermal cells with abundant microtubules. What is the primary function of these organelles in this context?
- A. Secreting chitin.
- B. Providing structural support for migration and changing cell shape.
- C. Digesting the old basement membrane.
- D. Storing lipids for energy.
- What specific structure was identified by electron microscopy as the primary “locomotory organelle” of migrating epidermal cells?
- A. Cilia.
- B. Ruffled membrane.
- C. Microvilli.
- D. Desmosome.
- The “new cuticle” is deposited by epidermal cells. At the ultrastructural level, how is this secretion accomplished efficiently?
- A. Through large, open pores in the cell membrane.
- B. By haemocytes, which transport it to the surface.
- C. Into the spaces between highly folded microvilli on the cell surface.
- D. The entire cell dissolves (holocrine secretion) to release the cuticle.
FAQs
Q: What is “ultrastructure”?
A: It refers to the fine-scale detail of a cell, visible only with an electron microscope, such as organelles (Golgi, ER) and membranes.
Q: What is the function of the Golgi bodies in these healing cells?
A: They “package” and “modify” the proteins and other materials synthesized by the cell (like in the RER) before they are secreted to form the new cuticle [p. 55].
Q: What is a “desmosome”?
A: It is a cell-to-cell junction, like a “spot weld.” The thesis observed them between migrating cells, showing they move as a connected sheet [p. 53].
Q: What did the basement membrane look like during migration?
A: It appeared “completely disorganised” and “fragmented,” allowing the cells to detach and move [p. 56-57].
Lab / Practical Note
Observing ultrastructure requires specialized tissue preparation for Transmission Electron Microscopy (TEM). Tissues must be fixed *immediately* to preserve delicate organelles. The thesis used a double-fixation method: first in 3.5% glutaraldehyde to cross-link proteins, followed by “post fixation” in 1% buffered osmium tetraoxide [p. 96]. The osmium both fixes lipids and adds electron density (stain), making membranes visible in the final micrograph.
External Resources
Cellular Ultrastructure (ScienceDirect)
The Mechanism of Cell Migration (NCBI)
Primary Thesis: Dutt, Archana. (1977). Healing of Cuticular Wounds in Arthropods (Summary). PhD Thesis, Department of Zoology, University of Lucknow, Lucknow (India). Supervisor: Dr. S. C. Srivastava.
Pages Used: This summary focuses primarily on the Electron Microscopy section (pp. 50-59, 96) and related discussion (pp. 6, 10, 73-77) of the original thesis pagination.
The Professor of Zoology editorial team has summarized this work for educational purposes. If you are the thesis author or copyright holder and wish to request corrections, please contact us at contact@professorofzoology.com. We invite institutional partners to contact us regarding hosting official abstracts.
Author: Archana Dutt, M.Sc. (1977)
Note: This summary was assisted by AI and verified by a human editor.
Reviewer: Abubakar Siddiq, PhD, Zoology.
Our editors have adapted this 1977 thesis summary for modern educational use. All interpretations are intended for study purposes.
Discover more from Professor Of Zoology
Subscribe to get the latest posts sent to your email.