Actl7a (rat, UniProt Q641W9) - manual literature synthesis

No deep-research provider was available for this session, so this synthesis was written by the
reviewer from cached publications (publications/PMID_*.md) and the UniProt record. Quotes are
verbatim from the cached text. The companion human review (genes/human/ACTL7A/) was consulted for
the structural audit and PAINT reading; facts reused from it are re-anchored here to primary papers.

Identity

• Rat Actl7a, Actin-like protein 7A (Arp7A, T-actin 2), 440 aa, RGD:1304697, GeneID 298017.
  Swiss-Prot reviewed, PE 1. Belongs to the actin family; carries the actin fold (Pfam PF00022) plus
  a unique N-terminal extension (Pfam PF16840, ACTL7A_N).
• The only experimental work on the rat protein itself is the co-immunoprecipitation from rat testis
  extracts in Boeda et al. 2011 PMID:21278383. All other functional knowledge comes from mouse knock-outs and human patients.

Molecular function

• The N-terminal extension binds the tandem LIM2-3 domains of testin (TES) [PMID:21278383 "The
  N-terminal 65-residue extension to the actin-like fold of Arp7A interacts directly with Tes.";
  "Two alanine residues from Arp7A that occupy equivalent apolar pockets in both LIM domains as well
  as an intervening GPAK linker that binds the LIM2-3 junction are critical for the Arp7A-Tes
  interaction."]. The binding assays and crystal structure used human Arp7A residues 1-65.
• Rat conservation (reviewer sequence check of the UniProt records): human residues 28-45
  (LQTASLRDGPAKRAVWVR) are identical in rat at residues 33-50, so the two apolar-pocket alanines
  (human A31/A41, rat A36/A46) and the GPAK linker (human 36-39, rat 41-44) are retained; the rat
  protein has a 5-residue longer N-terminus. The paper itself notes the extension is conserved
  PMID:21278383.
• Actin fold: no filament formation in cells PMID:21278383. Nucleotide binding
  and ATPase activity have never been measured. PAINT places GO:0005198 structural molecule activity
  on the ACTL7 node (PTN008986528) rather than the actin-specific structural constituent of
  cytoskeleton (see the human ACTL7A review notes for the PAINT table reading).
• Whether ACTL7A forms, nucleates or anchors subacrosomal F-actin is open PMID:36734600.

Location

• Subacrosomal layer (acroplaxome) of the perinuclear theca PMID:21278383. Immunofluorescence in this paper was on mouse testis sections
  ("Adult mouse testes were fixed in 4% paraformaldehyde"), not rat.
• Golgi apparatus during acrosome biogenesis PMID:21278383.
• Nucleus of germ cells (mouse) PMID:12672658; PMID:36734600.
• Sperm tail: reported only in the 2003 abstract PMID:12672658. The 2023 mouse study instead describes a connecting-piece
  pool, which GO does not place inside the flagellum (GO:0120212 sperm head-tail coupling apparatus
  has no part_of link to sperm flagellum).

Process (mouse genetics, human disease)

• Acrosome biogenesis and attachment PMID:36734600; subacrosomal F-actin is
  lost specifically PMID:36734600.
• Sperm head shaping PMID:37667331.
• Fertilization PMID:35921706; PLCzeta mislocalisation
  PMID:32923619.
• Partners in the perinuclear theca: CYLC1 PMID:38573307, FNDC8 PMID:41169243.

Gaps

• No rat-specific localisation, mutant or biochemical study exists.
• Nucleotide binding/hydrolysis and polymerisation behaviour of the actin fold are unmeasured.