You are currently on the new version of our website. Access the old version .
MDPIMDPI
Search all articles
by
  • María Jesús Ramírez-Expósito,
  • Cristina Cueto-Ureña and
  • José Manuel Martínez-Martos*

Reviewer 1: Anonymous Reviewer 2: Yizhou Zhuo Reviewer 3: Anonymous

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

As this is a review article, my questions are limited to certain details and are provided for reference only. I have following observations.

1 In Section 2.1,you discuss the interaction between presynaptic calcium channels and postsynaptic laminin β2. Does current evidence suggest that this anchoring mechanism is specific to excitatory synapses, or is it a universal feature of all central synapses?

2 Regarding the "lever hypothesis" for Synaptotagmin-1, how does this model reconcile with the varying calcium sensitivities observed in different modes of release (synchronous vs. asynchronous)?

3 In Section 2.3, you note that ultrafast endocytosis is triggered by strong stimulation. Could you further elaborate on the specific molecular "switch" that shifts a synapse from clathrin-mediated to ultrafast retrieval?

4 You describe the PSD as composed of heterogeneous nanoblocks. Given this heterogeneity, what is the turnover rate of these nanoblocks during a single Long-Term Potentiation (LTP) event?

5 Section 3.2.2 mentions DAPK1 recruitment to extrasynaptic GluN2B. Is this recruitment strictly a pathological event, or does DAPK1 play a refined role in physiological synaptic scaling?

6 You highlight that Pin1 recruitment is essential for structural remodeling of GABAergic synapses. How does this phosphorylation-dependent mechanism interact with the broader "gephyrin lattice" to maintain inhibitory stability?

7 The review notes that molecular diversity expansion requires a "unified model of synaptic homeostasis". When integrating complex molecular inventories across different laboratories and instruments, how should researchers address the inherent biological and instrumental variability?

Author Response

We would like to thank you for your insightful and constructive comments. Your expertise has significantly helped us refine the manuscript. Below are our point-by-point responses to your concerns:

  1. Presynaptic calcium channel anchoring mechanism. Section 2.1 clarifies that while laminin β2 is a key organizer at the NMJ, the core anchoring via RIM and RIM-BP scaffolds is a universal feature across all central synapses.
  2. Lever hypothesis and release modes. Section 2.2 specifies that the lever model governs synchronous release, while asynchronous release relies on high-affinity sensors like Syt7 or Doc2 to account for varying calcium sensitivities.
  3. Specific molecular "switch" for ultrafast endocytosis. Section 2.3 explicitly describes this switch as a mechanical "membrane compression model" driven by fused vesicles exerting lateral pressure against an F-actin-enriched zone.
  4. Turnover rate of nanobloques during LTP. Section 4.3 details that "nascent zones" are converted into functional active zones in less than 5 minutes to saturate potentiation capacity.
  5. Physiological role of DAPK1 in synaptic scaling. Section 3.2.2 highlights that DAPK1 serves as a refined physiological regulator during LTD, preventing CaMKII accumulation in the spine to enable bidirectional control of synaptic strength.
  6. Pin1 recruitment and gephyrin lattice stability. Section 3.3 describes how gephyrin phosphorylation recruits Pin1 and how variants like the C3 cassette reduce E-domain stability to balance inhibitory stability with remodeling.
  7. Addressing variability in the unified model. We propose that synaptic diversity must be normalized by the levels of core glutamate receptors to integrate complex molecular inventories into a unified homeostatic model.

Your constructive comments were truly encouraging. I would also like to thank you for the time you dedicated to reviewing this manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

The review by María Jesús Ramírez-Expósito et al., entitled “Molecular Physiology of the Neuronal Synapse,” provides a broad overview of the molecular composition of neuronal synapses and presents a generally comprehensive and accessible summary for a wide audience. The manuscript is overall well organized and clearly written. However, one major concern is that the diversity of synaptic mechanisms across different cell types and brain regions is not sufficiently discussed, which limits the depth and physiological relevance of the review.

 

Other minor comments:

 

  1. GPCR signaling is a core component of synaptic physiology and neuromodulation but is not sufficiently discussed. While PKA and PKC are mentioned, their roles are largely presented outside the context of GPCR signaling. It would be valuable for the authors to explicitly discuss GPCR-mediated pathways at synapses, including Gs/cAMP/PKA, Gi/o, and Gq/PLC/PKC signaling cascades, and how these pathways shape synaptic transmission and plasticity.
  2. The manuscript discusses the role of Synaptotagmin-1 (Syt-1) in synaptic vesicle release, which primarily applies to small synaptic vesicles. However, large dense-core vesicles (LDCVs) exhibit distinct release properties and rely more heavily on Synaptotagmin-7 (Syt-7), with Syt-1 playing a different or more limited role. Clarifying this distinction, or explicitly stating that the discussion focuses on small synaptic vesicles, would improve accuracy.
  3. Recent work (e.g., Jonathon et al., 2023, Nature; DOI: 10.1038/s41586-023-06465-y) suggests that CaMKII’s role in long-term potentiation is driven largely by structural rearrangements rather than enzymatic activity. This represents an important conceptual shift and would be a valuable addition to the discussion of synaptic plasticity mechanisms.
  4. Some sections contain repetitive or nearly identical descriptions. For example, the content in Lines 629–631 and Lines 466–469 appears substantially overlapping and could be streamlined to improve readability.
  5. The schematic summaries are visually appealing and helpful. However, the labeling is sometimes crowded and occasionally difficult to interpret. Consider improving clarity by making font colors consistent with the corresponding molecular components, adjusting label positions, adding arrows to guide readers more clearly.
  6. Careful proofreading is recommended, as there are several instances of unexpected or unclear text (e.g., Lines 440, 533, 614, 615).

Author Response

We are grateful for your thorough evaluation of our work.

Major Point:

  1. Synaptome Diversity: Now we integrate evidence regarding how the quantitative levels of shared components shape circuit-specific properties.

Minor Points:

  1. GPCR Signaling: We explicitly linked PKA/PKC to Gs/Gq cascades and highlighted the role of latrophilins/cAMP in initial assembly.
  2. SVs vs. LDCVs: Clarified the functional distinction between Syt1 and Syt7 and their respective membrane-binding redundancies.
  3. CaMKII in LTP: Updated the corresponding section to reflect the conceptual shift of CaMKII as a "structural seed" rather than a purely enzymatic actor.

Others:

We have removed the overlapping descriptions, refined the figures and corrected details according to your suggestions. Reference manager software codes were also corrected.

Your constructive comments were truly encouraging. I would also like to thank you for the time you dedicated to reviewing this manuscript.

Reviewer 3 Report

Comments and Suggestions for Authors

Section 2.1. Active zone organization and dynamics: How do voltage-gated calcium channels interact with laminin β2 to anchor the presynaptic complex?

Section 2.3. The vesicle recycling section mentions multiple pathways but doesn't discuss controversies around their relative contributions in vivo vs. in vitro models.

Section 5. Please explain how cell adhesion molecules such as neurexins and neuroligins guide synapse formation and elimination.

The keywords are appropriate, but adding "synaptic homeostasis" would improve discoverability.

Minor suggestions: Improve figure resolution in the PDF and ensure consistent formatting in tables. 

 

Author Response

We would like to thank you for your insightful and constructive comments. We have addressed them as follows:

  1. VGCC and Laminin β2 anchoring. According to your suggestions and the comments of other reviewers, the manuscript clarifies that RIM and RIM-BP scaffolds constitute the universal anchoring mechanism for CaV channels across all central synapses.
  2. Vesicle recycling controversies. We have updated the section discussing the in vivo vs. in vitro controversy, specifically highlighting how physiological temperatures and preparations favor ultrafast endocytosis over clathrin-mediated pathways.
  3. Neurexins/Neuroligins in formation and elimination. This section has been expanded to explain that these molecules specify synapse properties. We also clarify that synapse elimination is often triggered by the disengagement of these SAM signals, leading to secondary microglial recruitment.

Your constructive comments were truly encouraging. I would also like to thank you for the time you dedicated to reviewing this manuscript.